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* [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks
@ 2020-08-06 16:30 Derrick Stolee via GitGitGadget
  2020-08-06 16:30 ` [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
                   ` (9 more replies)
  0 siblings, 10 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee

This series is based on part I [2].

This patch series contains 9 patches that were going to be part of v4 of
ds/maintenance [1], but the discussion has gotten really long. To help, I'm
splitting out the portions that create and test the 'maintenance' builtin
from the additional tasks (prefetch, loose-objects, incremental-repack) that
can be brought in later.

[1] 
https://lore.kernel.org/git/pull.671.git.1594131695.gitgitgadget@gmail.com/
[2] 
https://lore.kernel.org/git/pull.695.git.1596728921.gitgitgadget@gmail.com/

As detailed in [2], the 'git maintenance run' subcommand will run certain
tasks based on config options or the --task= arguments. The --auto option
indicates to the task to only run based on some internal check that there
has been "enough" change in that domain to merit the work. In the case of
the 'gc' task, this also reduces the amount of work done. 

The new maintenance tasks in this series are:

 * 'loose-objects' : prune packed loose objects, then create a new pack from
   a batch of loose objects.
 * 'pack-files' : expire redundant packs from the multi-pack-index, then
   repack using the multi-pack-index's incremental repack strategy.
 * 'prefetch' : fetch from each remote, storing the refs in 'refs/prefetch/
   /'.

These tasks are all disabled by default, but can be enabled with config
options or run explicitly using "git maintenance run --task=". 

Since [2] replaced the 'git gc --auto' calls with 'git maintenance run
--auto' at the end of some Git commands, users could replace the 'gc' task
with these lighter-weight changes for foreground maintenance.

The 'git maintenance' builtin has a 'run' subcommand so it can be extended
later with subcommands that manage background maintenance, such as 'start'
or 'stop'. These are not the subject of this series, as it is important to
focus on the maintenance activities themselves. I have a WIP series for this
available at [3].

[3] https://github.com/gitgitgadget/git/pull/680

UPDATES since v3 of [1]
=======================

 * The biggest change here is the use of "test_subcommand", based on
   Jonathan Nieder's approach. This requires having the exact command-line
   figured out, which now requires spelling out all --no- [quiet%7Cprogress] 
   options. I also added a bunch of "2>/dev/null" checks because of the
   isatty(2) calls. Without that, the behavior will change depending on
   whether the test is run with -x/-v or without.
   
   
 * The 0x7FFF/0x7FFFFFFF constant problem is fixed with an EXPENSIVE test
   that verifies it.
   
   
 * The option parsing has changed to use a local struct and pass that struct
   to the helper methods. This is instead of having a global singleton.
   
   

Thanks, -Stolee

Here is the range-diff from the v3 of [1].

 1:  12fe73bb72 <  -:  ---------- maintenance: create basic maintenance runner
 2:  6e533e43d7 <  -:  ---------- maintenance: add --quiet option
 3:  c4674fc211 <  -:  ---------- maintenance: replace run_auto_gc()
 4:  b9332c1318 <  -:  ---------- maintenance: initialize task array
 5:  a4d9836bed <  -:  ---------- maintenance: add commit-graph task
 6:  dafb0d9bbc <  -:  ---------- maintenance: add --task option
 7:  1b00524da3 <  -:  ---------- maintenance: take a lock on the objects directory
 8:  0e94e04dcd =  1:  83401c5200 fetch: optionally allow disabling FETCH_HEAD update
 9:  9e38ade15c !  2:  85118ed5f1 maintenance: add prefetch task
    @@ Documentation/git-maintenance.txt: since it will not expire `.graph` files that

      ## builtin/gc.c ##
     @@
    - #include "blob.h"
      #include "tree.h"
      #include "promisor-remote.h"
    + #include "refs.h"
     +#include "remote.h"

      #define FAILED_RUN "failed to run %s"

    -@@ builtin/gc.c: static int maintenance_task_commit_graph(void)
    +@@ builtin/gc.c: static int maintenance_task_commit_graph(struct maintenance_opts *opts)
          return 1;
      }

    -+static int fetch_remote(const char *remote)
    ++static int fetch_remote(const char *remote, struct maintenance_opts *opts)
     +{
     +    struct child_process child = CHILD_PROCESS_INIT;
     +
    @@ builtin/gc.c: static int maintenance_task_commit_graph(void)
     +    strvec_pushl(&child.args, "fetch", remote, "--prune", "--no-tags",
     +             "--no-write-fetch-head", "--refmap=", NULL);
     +
    -+    strvec_pushf(&child.args, "+refs/heads/*:refs/prefetch/%s/*", remote);
    -+
    -+    if (opts.quiet)
    ++    if (opts->quiet)
     +        strvec_push(&child.args, "--quiet");
     +
    ++    strvec_pushf(&child.args, "+refs/heads/*:refs/prefetch/%s/*", remote);
    ++
     +    return !!run_command(&child);
     +}
     +
    @@ builtin/gc.c: static int maintenance_task_commit_graph(void)
     +    return 0;
     +}
     +
    -+static int maintenance_task_prefetch(void)
    ++static int maintenance_task_prefetch(struct maintenance_opts *opts)
     +{
     +    int result = 0;
     +    struct string_list_item *item;
    @@ builtin/gc.c: static int maintenance_task_commit_graph(void)
     +    for (item = remotes.items;
     +         item && item < remotes.items + remotes.nr;
     +         item++)
    -+        result |= fetch_remote(item->string);
    ++        result |= fetch_remote(item->string, opts);
     +
     +cleanup:
     +    string_list_clear(&remotes, 0);
     +    return result;
     +}
     +
    - static int maintenance_task_gc(void)
    + static int maintenance_task_gc(struct maintenance_opts *opts)
      {
          struct child_process child = CHILD_PROCESS_INIT;
     @@ builtin/gc.c: struct maintenance_task {
    @@ t/t7900-maintenance.sh: test_expect_success 'run --task duplicate' '
     +    git -C clone2 switch -c two &&
     +    test_commit -C clone1 one &&
     +    test_commit -C clone2 two &&
    -+    GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch &&
    -+    grep ",\"fetch\",\"remote1\"" run-prefetch.txt &&
    -+    grep ",\"fetch\",\"remote2\"" run-prefetch.txt &&
    ++    GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null &&
    ++    fetchargs="--prune --no-tags --no-write-fetch-head --refmap= --quiet" &&
    ++    test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\* <run-prefetch.txt &&
    ++    test_subcommand git fetch remote2 $fetchargs +refs/heads/\\*:refs/prefetch/remote2/\\* <run-prefetch.txt &&
     +    test_path_is_missing .git/refs/remotes &&
     +    test_cmp clone1/.git/refs/heads/one .git/refs/prefetch/remote1/one &&
     +    test_cmp clone2/.git/refs/heads/two .git/refs/prefetch/remote2/two &&
10:  0128fdfd1a !  3:  621375a3c9 maintenance: add loose-objects task
    @@ Documentation/git-maintenance.txt: gc::
      --auto::

      ## builtin/gc.c ##
    -@@ builtin/gc.c: static int maintenance_task_gc(void)
    +@@ builtin/gc.c: static int maintenance_task_gc(struct maintenance_opts *opts)
          return run_command(&child);
      }

    -+static int prune_packed(void)
    ++static int prune_packed(struct maintenance_opts *opts)
     +{
     +    struct child_process child = CHILD_PROCESS_INIT;
     +
     +    child.git_cmd = 1;
     +    strvec_push(&child.args, "prune-packed");
     +
    -+    if (opts.quiet)
    ++    if (opts->quiet)
     +        strvec_push(&child.args, "--quiet");
     +
     +    return !!run_command(&child);
    @@ builtin/gc.c: static int maintenance_task_gc(void)
     +    return ++(d->count) > d->batch_size;
     +}
     +
    -+static int pack_loose(void)
    ++static int pack_loose(struct maintenance_opts *opts)
     +{
     +    struct repository *r = the_repository;
     +    int result = 0;
    @@ builtin/gc.c: static int maintenance_task_gc(void)
     +    pack_proc.git_cmd = 1;
     +
     +    strvec_push(&pack_proc.args, "pack-objects");
    -+    if (opts.quiet)
    ++    if (opts->quiet)
     +        strvec_push(&pack_proc.args, "--quiet");
     +    strvec_pushf(&pack_proc.args, "%s/pack/loose", r->objects->odb->path);
     +
    @@ builtin/gc.c: static int maintenance_task_gc(void)
     +    return result;
     +}
     +
    -+static int maintenance_task_loose_objects(void)
    ++static int maintenance_task_loose_objects(struct maintenance_opts *opts)
     +{
    -+    return prune_packed() || pack_loose();
    ++    return prune_packed(opts) || pack_loose(opts);
     +}
     +
    - typedef int maintenance_task_fn(void);
    + typedef int maintenance_task_fn(struct maintenance_opts *opts);

    - struct maintenance_task {
    + /*
     @@ builtin/gc.c: struct maintenance_task {

      enum maintenance_task_label {
17:  6ac3a58f2f !  4:  e787403ea7 maintenance: create auto condition for loose-objects
    @@ builtin/gc.c: static struct maintenance_task tasks[] = {
              maintenance_task_loose_objects,
     +        loose_object_auto_condition,
          },
    -     [TASK_INCREMENTAL_REPACK] = {
    -         "incremental-repack",
    +     [TASK_GC] = {
    +         "gc",

      ## t/t7900-maintenance.sh ##
     @@ t/t7900-maintenance.sh: test_expect_success 'loose-objects task' '
    @@ t/t7900-maintenance.sh: test_expect_success 'loose-objects task' '
     +    git repack -adk &&
     +    GIT_TRACE2_EVENT="$(pwd)/trace-lo1.txt" \
     +        git -c maintenance.loose-objects.auto=1 maintenance \
    -+        run --auto --task=loose-objects &&
    -+    ! grep "\"prune-packed\"" trace-lo1.txt &&
    ++        run --auto --task=loose-objects 2>/dev/null &&
    ++    test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
     +    for i in 1 2
     +    do
     +        printf data-A-$i | git hash-object -t blob --stdin -w &&
     +        GIT_TRACE2_EVENT="$(pwd)/trace-loA-$i" \
     +            git -c maintenance.loose-objects.auto=2 \
    -+            maintenance run --auto --task=loose-objects &&
    -+        ! grep "\"prune-packed\"" trace-loA-$i &&
    ++            maintenance run --auto --task=loose-objects 2>/dev/null &&
    ++        test_subcommand ! git prune-packed --quiet <trace-loA-$i &&
     +        printf data-B-$i | git hash-object -t blob --stdin -w &&
     +        GIT_TRACE2_EVENT="$(pwd)/trace-loB-$i" \
     +            git -c maintenance.loose-objects.auto=2 \
    -+            maintenance run --auto --task=loose-objects &&
    -+        grep "\"prune-packed\"" trace-loB-$i &&
    ++            maintenance run --auto --task=loose-objects 2>/dev/null &&
    ++        test_subcommand git prune-packed --quiet <trace-loB-$i &&
     +        GIT_TRACE2_EVENT="$(pwd)/trace-loC-$i" \
     +            git -c maintenance.loose-objects.auto=2 \
    -+            maintenance run --auto --task=loose-objects &&
    -+        grep "\"prune-packed\"" trace-loC-$i || return 1
    ++            maintenance run --auto --task=loose-objects 2>/dev/null &&
    ++        test_subcommand git prune-packed --quiet <trace-loC-$i || return 1
     +    done
     +'
     +
    - test_expect_success 'incremental-repack task' '
    -     packDir=.git/objects/pack &&
    -     for i in $(test_seq 1 5)
    + test_done
11:  c2baf6e119 =  5:  37e59b1a8d midx: enable core.multiPackIndex by default
19:  9b4cef7635 =  6:  aba087f663 midx: use start_delayed_progress()
12:  00f47c4848 !  7:  68727c555b maintenance: add incremental-repack task
    @@ Documentation/git-maintenance.txt: loose-objects::

      ## builtin/gc.c ##
     @@
    - #include "tree.h"
      #include "promisor-remote.h"
    + #include "refs.h"
      #include "remote.h"
     +#include "midx.h"

      #define FAILED_RUN "failed to run %s"

    -@@ builtin/gc.c: static int maintenance_task_loose_objects(void)
    -     return prune_packed() || pack_loose();
    +@@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_opts *opts)
    +     return prune_packed(opts) || pack_loose(opts);
      }

    -+static int multi_pack_index_write(void)
    ++static int multi_pack_index_write(struct maintenance_opts *opts)
     +{
     +    struct child_process child = CHILD_PROCESS_INIT;
     +
     +    child.git_cmd = 1;
     +    strvec_pushl(&child.args, "multi-pack-index", "write", NULL);
     +
    -+    if (opts.quiet)
    ++    if (opts->quiet)
     +        strvec_push(&child.args, "--no-progress");
     +
     +    if (run_command(&child))
    @@ builtin/gc.c: static int maintenance_task_loose_objects(void)
     +    return 0;
     +}
     +
    -+static int rewrite_multi_pack_index(void)
    ++static int rewrite_multi_pack_index(struct maintenance_opts *opts)
     +{
     +    struct repository *r = the_repository;
     +    char *midx_name = get_midx_filename(r->objects->odb->path);
    @@ builtin/gc.c: static int maintenance_task_loose_objects(void)
     +    unlink(midx_name);
     +    free(midx_name);
     +
    -+    return multi_pack_index_write();
    ++    return multi_pack_index_write(opts);
     +}
     +
    -+static int multi_pack_index_verify(const char *message)
    ++static int multi_pack_index_verify(struct maintenance_opts *opts,
    ++                   const char *message)
     +{
     +    struct child_process child = CHILD_PROCESS_INIT;
     +
     +    child.git_cmd = 1;
     +    strvec_pushl(&child.args, "multi-pack-index", "verify", NULL);
     +
    -+    if (opts.quiet)
    ++    if (opts->quiet)
     +        strvec_push(&child.args, "--no-progress");
     +
     +    if (run_command(&child)) {
    @@ builtin/gc.c: static int maintenance_task_loose_objects(void)
     +    return 0;
     +}
     +
    -+static int multi_pack_index_expire(void)
    ++static int multi_pack_index_expire(struct maintenance_opts *opts)
     +{
     +    struct child_process child = CHILD_PROCESS_INIT;
     +
     +    child.git_cmd = 1;
     +    strvec_pushl(&child.args, "multi-pack-index", "expire", NULL);
     +
    -+    if (opts.quiet)
    ++    if (opts->quiet)
     +        strvec_push(&child.args, "--no-progress");
     +
     +    close_object_store(the_repository->objects);
    @@ builtin/gc.c: static int maintenance_task_loose_objects(void)
     +    return 0;
     +}
     +
    -+static int multi_pack_index_repack(void)
    ++static int multi_pack_index_repack(struct maintenance_opts *opts)
     +{
     +    struct child_process child = CHILD_PROCESS_INIT;
     +
     +    child.git_cmd = 1;
     +    strvec_pushl(&child.args, "multi-pack-index", "repack", NULL);
     +
    -+    if (opts.quiet)
    ++    if (opts->quiet)
     +        strvec_push(&child.args, "--no-progress");
     +
     +    strvec_push(&child.args, "--batch-size=0");
    @@ builtin/gc.c: static int maintenance_task_loose_objects(void)
     +    return 0;
     +}
     +
    -+static int maintenance_task_incremental_repack(void)
    ++static int maintenance_task_incremental_repack(struct maintenance_opts *opts)
     +{
     +    prepare_repo_settings(the_repository);
     +    if (!the_repository->settings.core_multi_pack_index) {
    @@ builtin/gc.c: static int maintenance_task_loose_objects(void)
     +        return 0;
     +    }
     +
    -+    if (multi_pack_index_write())
    ++    if (multi_pack_index_write(opts))
     +        return 1;
    -+    if (multi_pack_index_verify("after initial write"))
    -+        return rewrite_multi_pack_index();
    -+    if (multi_pack_index_expire())
    ++    if (multi_pack_index_verify(opts, "after initial write"))
    ++        return rewrite_multi_pack_index(opts);
    ++    if (multi_pack_index_expire(opts))
     +        return 1;
    -+    if (multi_pack_index_verify("after expire step"))
    -+        return !!rewrite_multi_pack_index();
    -+    if (multi_pack_index_repack())
    ++    if (multi_pack_index_verify(opts, "after expire step"))
    ++        return !!rewrite_multi_pack_index(opts);
    ++    if (multi_pack_index_repack(opts))
     +        return 1;
    -+    if (multi_pack_index_verify("after repack step"))
    -+        return !!rewrite_multi_pack_index();
    ++    if (multi_pack_index_verify(opts, "after repack step"))
    ++        return !!rewrite_multi_pack_index(opts);
     +    return 0;
     +}
     +
    - typedef int maintenance_task_fn(void);
    + typedef int maintenance_task_fn(struct maintenance_opts *opts);

    - struct maintenance_task {
    + /*
     @@ builtin/gc.c: struct maintenance_task {
      enum maintenance_task_label {
          TASK_PREFETCH,
    @@ builtin/gc.c: struct maintenance_task {
          TASK_COMMIT_GRAPH,

     @@ builtin/gc.c: static struct maintenance_task tasks[] = {
    -         "loose-objects",
              maintenance_task_loose_objects,
    +         loose_object_auto_condition,
          },
     +    [TASK_INCREMENTAL_REPACK] = {
     +        "incremental-repack",
    @@ t/t7900-maintenance.sh: test_description='git maintenance builtin'

      test_expect_success 'help text' '
          test_expect_code 129 git maintenance -h 2>err &&
    -@@ t/t7900-maintenance.sh: test_expect_success 'loose-objects task' '
    -     test_cmp packs-between packs-after
    +@@ t/t7900-maintenance.sh: test_expect_success 'maintenance.loose-objects.auto' '
    +     done
      '

     +test_expect_success 'incremental-repack task' '
13:  ef2a231956 !  8:  c3487fb8e3 maintenance: auto-size incremental-repack batch
    @@ Commit message
         truly want to optimize for space and performance (and are willing to pay
         the upfront cost of a full repack) can use the 'gc' task to do so.

    +    Create a test for this two gigabyte limit by creating an EXPENSIVE test
    +    that generates two pack-files of roughly 2.5 gigabytes in size, then
    +    performs an incremental repack. Check that the --batch-size argument in
    +    the subcommand uses the hard-coded maximum.
    +
    +    Helped-by: Chris Torek <chris.torek@gmail.com>
         Reported-by: Son Luong Ngoc <sluongng@gmail.com>
         Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

      ## builtin/gc.c ##
    -@@ builtin/gc.c: static int multi_pack_index_expire(void)
    +@@ builtin/gc.c: static int multi_pack_index_expire(struct maintenance_opts *opts)
          return 0;
      }

    -+#define TWO_GIGABYTES (0x7FFF)
    ++#define TWO_GIGABYTES (INT32_MAX)
     +
     +static off_t get_auto_pack_size(void)
     +{
    @@ builtin/gc.c: static int multi_pack_index_expire(void)
     +    return result_size;
     +}
     +
    - static int multi_pack_index_repack(void)
    + static int multi_pack_index_repack(struct maintenance_opts *opts)
      {
          struct child_process child = CHILD_PROCESS_INIT;
    -@@ builtin/gc.c: static int multi_pack_index_repack(void)
    -     if (opts.quiet)
    +@@ builtin/gc.c: static int multi_pack_index_repack(struct maintenance_opts *opts)
    +     if (opts->quiet)
              strvec_push(&child.args, "--no-progress");

     -    strvec_push(&child.args, "--batch-size=0");
    @@ t/t7900-maintenance.sh: test_expect_success 'incremental-repack task' '
          ls .git/objects/pack/*.pack >packs-after &&
     -    test_line_count = 1 packs-after
     +    test_line_count = 2 packs-after
    ++'
    ++
    ++test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
    ++    for i in $(test_seq 1 5)
    ++    do
    ++        test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
    ++        return 1
    ++    done &&
    ++    git add big &&
    ++    git commit -m "Add big file (1)" &&
    ++
    ++    # ensure any possible loose objects are in a pack-file
    ++    git maintenance run --task=loose-objects &&
    ++
    ++    rm big &&
    ++    for i in $(test_seq 6 10)
    ++    do
    ++        test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
    ++        return 1
    ++    done &&
    ++    git add big &&
    ++    git commit -m "Add big file (2)" &&
    ++
    ++    # ensure any possible loose objects are in a pack-file
    ++    git maintenance run --task=loose-objects &&
    ++
    ++    # Now run the incremental-repack task and check the batch-size
    ++    GIT_TRACE2_EVENT="$(pwd)/run-2g.txt" git maintenance run \
    ++        --task=incremental-repack 2>/dev/null &&
    ++    test_subcommand git multi-pack-index repack \
    ++         --no-progress --batch-size=2147483647 <run-2g.txt
      '

      test_done
14:  99840c4b8f <  -:  ---------- maintenance: create maintenance.<task>.enabled config
15:  a087c63572 <  -:  ---------- maintenance: use pointers to check --auto
16:  ef3a854508 <  -:  ---------- maintenance: add auto condition for commit-graph task
18:  801b262d1c !  9:  407c123c51 maintenance: add incremental-repack auto condition
    @@ Documentation/config/maintenance.txt: maintenance.loose-objects.auto::

      ## builtin/gc.c ##
     @@
    + #include "refs.h"
      #include "remote.h"
      #include "midx.h"
    - #include "refs.h"
     +#include "object-store.h"

      #define FAILED_RUN "failed to run %s"

    -@@ builtin/gc.c: static int maintenance_task_loose_objects(void)
    -     return prune_packed() || pack_loose();
    +@@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_opts *opts)
    +     return prune_packed(opts) || pack_loose(opts);
      }

     +static int incremental_repack_auto_condition(void)
    @@ builtin/gc.c: static int maintenance_task_loose_objects(void)
     +    return count >= incremental_repack_auto_limit;
     +}
     +
    - static int multi_pack_index_write(void)
    + static int multi_pack_index_write(struct maintenance_opts *opts)
      {
          struct child_process child = CHILD_PROCESS_INIT;
     @@ builtin/gc.c: static struct maintenance_task tasks[] = {
    @@ builtin/gc.c: static struct maintenance_task tasks[] = {

      ## t/t7900-maintenance.sh ##
     @@ t/t7900-maintenance.sh: test_expect_success 'incremental-repack task' '
    -     test_line_count = 2 packs-after
    + '
    + 
    + test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
    ++
    +     for i in $(test_seq 1 5)
    +     do
    +         test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
    +@@ t/t7900-maintenance.sh: test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
    +          --no-progress --batch-size=2147483647 <run-2g.txt
      '

     +test_expect_success 'maintenance.incremental-repack.auto' '
     +    git repack -adk &&
     +    git config core.multiPackIndex true &&
     +    git multi-pack-index write &&
    -+    GIT_TRACE2_EVENT=1 git -c maintenance.incremental-repack.auto=1 \
    -+        maintenance run --auto --task=incremental-repack >out &&
    -+    ! grep "\"multi-pack-index\"" out &&
    ++    GIT_TRACE2_EVENT="$(pwd)/midx-init.txt" git \
    ++        -c maintenance.incremental-repack.auto=1 \
    ++        maintenance run --auto --task=incremental-repack 2>/dev/null &&
    ++    test_subcommand ! git multi-pack-index write --no-progress <midx-init.txt &&
     +    for i in 1 2
     +    do
     +        test_commit A-$i &&
    @@ t/t7900-maintenance.sh: test_expect_success 'incremental-repack task' '
     +        EOF
     +        GIT_TRACE2_EVENT=$(pwd)/trace-A-$i git \
     +            -c maintenance.incremental-repack.auto=2 \
    -+            maintenance run --auto --task=incremental-repack &&
    -+        ! grep "\"multi-pack-index\"" trace-A-$i &&
    ++            maintenance run --auto --task=incremental-repack 2>/dev/null &&
    ++        test_subcommand ! git multi-pack-index write --no-progress <trace-A-$i &&
     +        test_commit B-$i &&
     +        git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
     +        HEAD
    @@ t/t7900-maintenance.sh: test_expect_success 'incremental-repack task' '
     +        EOF
     +        GIT_TRACE2_EVENT=$(pwd)/trace-B-$i git \
     +            -c maintenance.incremental-repack.auto=2 \
    -+            maintenance run --auto --task=incremental-repack >out &&
    -+        grep "\"multi-pack-index\"" trace-B-$i >/dev/null || return 1
    ++            maintenance run --auto --task=incremental-repack 2>/dev/null &&
    ++        test_subcommand git multi-pack-index write --no-progress <trace-B-$i || return 1
     +    done
     +'
     +
20:  39eb83ad1e <  -:  ---------- maintenance: add trace2 regions for task execution

Derrick Stolee (8):
  maintenance: add prefetch task
  maintenance: add loose-objects task
  maintenance: create auto condition for loose-objects
  midx: enable core.multiPackIndex by default
  midx: use start_delayed_progress()
  maintenance: add incremental-repack task
  maintenance: auto-size incremental-repack batch
  maintenance: add incremental-repack auto condition

Junio C Hamano (1):
  fetch: optionally allow disabling FETCH_HEAD update

 Documentation/config/core.txt        |   4 +-
 Documentation/config/fetch.txt       |   7 +
 Documentation/config/maintenance.txt |  18 ++
 Documentation/fetch-options.txt      |  10 +
 Documentation/git-maintenance.txt    |  41 +++
 builtin/fetch.c                      |  19 +-
 builtin/gc.c                         | 364 +++++++++++++++++++++++++++
 builtin/pull.c                       |   3 +-
 midx.c                               |  23 +-
 midx.h                               |   1 +
 repo-settings.c                      |   6 +
 repository.h                         |   2 +
 t/t5319-multi-pack-index.sh          |  15 +-
 t/t5510-fetch.sh                     |  39 ++-
 t/t5521-pull-options.sh              |  16 ++
 t/t7900-maintenance.sh               | 191 ++++++++++++++
 16 files changed, 730 insertions(+), 29 deletions(-)


base-commit: a5d19148460decaf08e0e6293e996d42ff3f2d32
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-696%2Fderrickstolee%2Fmaintenance%2Fgc-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-696/derrickstolee/maintenance/gc-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/696
-- 
gitgitgadget

^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
@ 2020-08-06 16:30 ` Junio C Hamano via GitGitGadget
  2020-08-12 23:10   ` Emily Shaffer
  2020-08-06 16:30 ` [PATCH 2/9] maintenance: add prefetch task Derrick Stolee via GitGitGadget
                   ` (8 subsequent siblings)
  9 siblings, 1 reply; 66+ messages in thread
From: Junio C Hamano via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Junio C Hamano

From: Junio C Hamano <gitster@pobox.com>

If you run fetch but record the result in remote-tracking branches,
and either if you do nothing with the fetched refs (e.g. you are
merely mirroring) or if you always work from the remote-tracking
refs (e.g. you fetch and then merge origin/branchname separately),
you can get away with having no FETCH_HEAD at all.

Teach "git fetch" a command line option "--[no-]write-fetch-head"
and "fetch.writeFetchHEAD" configuration variable.  Without either,
the default is to write FETCH_HEAD, and the usual rule that the
command line option defeats configured default applies.

Note that under "--dry-run" mode, FETCH_HEAD is never written;
otherwise you'd see list of objects in the file that you do not
actually have.  Passing `--write-fetch-head` does not force `git
fetch` to write the file.

Also note that this option is explicitly passed when "git pull"
internally invokes "git fetch", so that those who configured their
"git fetch" not to write FETCH_HEAD would not be able to break the
cooperation between these two commands.  "git pull" must see what
"git fetch" got recorded in FETCH_HEAD to work correctly.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/fetch.txt  |  7 ++++++
 Documentation/fetch-options.txt | 10 +++++++++
 builtin/fetch.c                 | 19 +++++++++++++---
 builtin/pull.c                  |  3 ++-
 t/t5510-fetch.sh                | 39 +++++++++++++++++++++++++++++++--
 t/t5521-pull-options.sh         | 16 ++++++++++++++
 6 files changed, 88 insertions(+), 6 deletions(-)

diff --git a/Documentation/config/fetch.txt b/Documentation/config/fetch.txt
index b20394038d..0aaa05e8c0 100644
--- a/Documentation/config/fetch.txt
+++ b/Documentation/config/fetch.txt
@@ -91,3 +91,10 @@ fetch.writeCommitGraph::
 	merge and the write may take longer. Having an updated commit-graph
 	file helps performance of many Git commands, including `git merge-base`,
 	`git push -f`, and `git log --graph`. Defaults to false.
+
+fetch.writeFetchHEAD::
+	Setting it to false tells `git fetch` not to write the list
+	of remote refs fetched in the `FETCH_HEAD` file directly
+	under `$GIT_DIR`.  Can be countermanded from the command
+	line with the `--[no-]write-fetch-head` option.  Defaults to
+	true.
diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index 495bc8ab5a..6972ad2522 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -64,6 +64,16 @@ documented in linkgit:git-config[1].
 --dry-run::
 	Show what would be done, without making any changes.
 
+ifndef::git-pull[]
+--[no-]write-fetch-head::
+	Write the list of remote refs fetched in the `FETCH_HEAD`
+	file directly under `$GIT_DIR`.  This is the default unless
+	the configuration variable `fetch.writeFetchHEAD` is set to
+	false.  Passing `--no-write-fetch-head` from the command
+	line tells Git not to write the file.  Under `--dry-run`
+	option, the file is never written.
+endif::git-pull[]
+
 -f::
 --force::
 	When 'git fetch' is used with `<src>:<dst>` refspec it may
diff --git a/builtin/fetch.c b/builtin/fetch.c
index c8b9366d3c..42ca774ad1 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -56,6 +56,7 @@ static int prune_tags = -1; /* unspecified */
 #define PRUNE_TAGS_BY_DEFAULT 0 /* do we prune tags by default? */
 
 static int all, append, dry_run, force, keep, multiple, update_head_ok;
+static int write_fetch_head = 1;
 static int verbosity, deepen_relative, set_upstream;
 static int progress = -1;
 static int enable_auto_gc = 1;
@@ -118,6 +119,10 @@ static int git_fetch_config(const char *k, const char *v, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(k, "fetch.writefetchhead")) {
+		write_fetch_head = git_config_bool(k, v);
+		return 0;
+	}
 	return git_default_config(k, v, cb);
 }
 
@@ -162,6 +167,8 @@ static struct option builtin_fetch_options[] = {
 		    PARSE_OPT_OPTARG, option_fetch_parse_recurse_submodules),
 	OPT_BOOL(0, "dry-run", &dry_run,
 		 N_("dry run")),
+	OPT_BOOL(0, "write-fetch-head", &write_fetch_head,
+		 N_("write fetched references to the FETCH_HEAD file")),
 	OPT_BOOL('k', "keep", &keep, N_("keep downloaded pack")),
 	OPT_BOOL('u', "update-head-ok", &update_head_ok,
 		    N_("allow updating of HEAD ref")),
@@ -895,7 +902,9 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 	const char *what, *kind;
 	struct ref *rm;
 	char *url;
-	const char *filename = dry_run ? "/dev/null" : git_path_fetch_head(the_repository);
+	const char *filename = (!write_fetch_head
+				? "/dev/null"
+				: git_path_fetch_head(the_repository));
 	int want_status;
 	int summary_width = transport_summary_width(ref_map);
 
@@ -1329,7 +1338,7 @@ static int do_fetch(struct transport *transport,
 	}
 
 	/* if not appending, truncate FETCH_HEAD */
-	if (!append && !dry_run) {
+	if (!append && write_fetch_head) {
 		retcode = truncate_fetch_head();
 		if (retcode)
 			goto cleanup;
@@ -1596,7 +1605,7 @@ static int fetch_multiple(struct string_list *list, int max_children)
 	int i, result = 0;
 	struct strvec argv = STRVEC_INIT;
 
-	if (!append && !dry_run) {
+	if (!append && write_fetch_head) {
 		int errcode = truncate_fetch_head();
 		if (errcode)
 			return errcode;
@@ -1797,6 +1806,10 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	if (depth || deepen_since || deepen_not.nr)
 		deepen = 1;
 
+	/* FETCH_HEAD never gets updated in --dry-run mode */
+	if (dry_run)
+		write_fetch_head = 0;
+
 	if (all) {
 		if (argc == 1)
 			die(_("fetch --all does not take a repository argument"));
diff --git a/builtin/pull.c b/builtin/pull.c
index 015f6ded0b..5ef3434e1f 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -527,7 +527,8 @@ static int run_fetch(const char *repo, const char **refspecs)
 	struct strvec args = STRVEC_INIT;
 	int ret;
 
-	strvec_pushl(&args, "fetch", "--update-head-ok", NULL);
+	strvec_pushl(&args, "fetch", "--update-head-ok",
+		     "--write-fetch-head", NULL);
 
 	/* Shared options */
 	argv_push_verbosity(&args);
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 9850ecde5d..31c91d0ed2 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -539,13 +539,48 @@ test_expect_success 'fetch into the current branch with --update-head-ok' '
 
 '
 
-test_expect_success 'fetch --dry-run' '
-
+test_expect_success 'fetch --dry-run does not touch FETCH_HEAD' '
 	rm -f .git/FETCH_HEAD &&
 	git fetch --dry-run . &&
 	! test -f .git/FETCH_HEAD
 '
 
+test_expect_success '--no-write-fetch-head does not touch FETCH_HEAD' '
+	rm -f .git/FETCH_HEAD &&
+	git fetch --no-write-fetch-head . &&
+	! test -f .git/FETCH_HEAD
+'
+
+test_expect_success '--write-fetch-head gets defeated by --dry-run' '
+	rm -f .git/FETCH_HEAD &&
+	git fetch --dry-run --write-fetch-head . &&
+	! test -f .git/FETCH_HEAD
+'
+
+test_expect_success 'fetch.writeFetchHEAD and FETCH_HEAD' '
+	rm -f .git/FETCH_HEAD &&
+	git -c fetch.writeFetchHEAD=no fetch . &&
+	! test -f .git/FETCH_HEAD
+'
+
+test_expect_success 'fetch.writeFetchHEAD gets defeated by --dry-run' '
+	rm -f .git/FETCH_HEAD &&
+	git -c fetch.writeFetchHEAD=yes fetch --dry-run . &&
+	! test -f .git/FETCH_HEAD
+'
+
+test_expect_success 'fetch.writeFetchHEAD and --no-write-fetch-head' '
+	rm -f .git/FETCH_HEAD &&
+	git -c fetch.writeFetchHEAD=yes fetch --no-write-fetch-head . &&
+	! test -f .git/FETCH_HEAD
+'
+
+test_expect_success 'fetch.writeFetchHEAD and --write-fetch-head' '
+	rm -f .git/FETCH_HEAD &&
+	git -c fetch.writeFetchHEAD=no fetch --write-fetch-head . &&
+	test -f .git/FETCH_HEAD
+'
+
 test_expect_success "should be able to fetch with duplicate refspecs" '
 	mkdir dups &&
 	(
diff --git a/t/t5521-pull-options.sh b/t/t5521-pull-options.sh
index 159afa7ac8..1acae3b9a4 100755
--- a/t/t5521-pull-options.sh
+++ b/t/t5521-pull-options.sh
@@ -77,6 +77,7 @@ test_expect_success 'git pull -q -v --no-rebase' '
 	test_must_be_empty out &&
 	test -s err)
 '
+
 test_expect_success 'git pull --cleanup errors early on invalid argument' '
 	mkdir clonedcleanup &&
 	(cd clonedcleanup && git init &&
@@ -85,6 +86,21 @@ test_expect_success 'git pull --cleanup errors early on invalid argument' '
 	test -s err)
 '
 
+test_expect_success 'git pull --no-write-fetch-head fails' '
+	mkdir clonedwfh &&
+	(cd clonedwfh && git init &&
+	test_must_fail git pull --no-write-fetch-head "../parent" >out 2>err &&
+	test_must_be_empty out &&
+	test_i18ngrep "no-write-fetch-head" err)
+'
+
+test_expect_success 'git pull succeeds with fetch.writeFetchHEAD=false' '
+	mkdir clonedwfhconfig &&
+	(cd clonedwfhconfig && git init &&
+	git config fetch.writeFetchHEAD false &&
+	git pull "../parent" >out 2>err &&
+	grep FETCH_HEAD err)
+'
 
 test_expect_success 'git pull --force' '
 	mkdir clonedoldstyle &&
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH 2/9] maintenance: add prefetch task
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  2020-08-06 16:30 ` [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
@ 2020-08-06 16:30 ` Derrick Stolee via GitGitGadget
  2020-08-12 23:10   ` Emily Shaffer
  2020-08-06 16:30 ` [PATCH 3/9] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
                   ` (7 subsequent siblings)
  9 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

When working with very large repositories, an incremental 'git fetch'
command can download a large amount of data. If there are many other
users pushing to a common repo, then this data can rival the initial
pack-file size of a 'git clone' of a medium-size repo.

Users may want to keep the data on their local repos as close as
possible to the data on the remote repos by fetching periodically in
the background. This can break up a large daily fetch into several
smaller hourly fetches.

The task is called "prefetch" because it is work done in advance
of a foreground fetch to make that 'git fetch' command much faster.

However, if we simply ran 'git fetch <remote>' in the background,
then the user running a foregroudn 'git fetch <remote>' would lose
some important feedback when a new branch appears or an existing
branch updates. This is especially true if a remote branch is
force-updated and this isn't noticed by the user because it occurred
in the background. Further, the functionality of 'git push
--force-with-lease' becomes suspect.

When running 'git fetch <remote> <options>' in the background, use
the following options for careful updating:

1. --no-tags prevents getting a new tag when a user wants to see
   the new tags appear in their foreground fetches.

2. --refmap= removes the configured refspec which usually updates
   refs/remotes/<remote>/* with the refs advertised by the remote.
   While this looks confusing, this was documented and tested by
   b40a50264ac (fetch: document and test --refmap="", 2020-01-21),
   including this sentence in the documentation:

	Providing an empty `<refspec>` to the `--refmap` option
	causes Git to ignore the configured refspecs and rely
	entirely on the refspecs supplied as command-line arguments.

3. By adding a new refspec "+refs/heads/*:refs/prefetch/<remote>/*"
   we can ensure that we actually load the new values somewhere in
   our refspace while not updating refs/heads or refs/remotes. By
   storing these refs here, the commit-graph job will update the
   commit-graph with the commits from these hidden refs.

4. --prune will delete the refs/prefetch/<remote> refs that no
   longer appear on the remote.

5. --no-write-fetch-head prevents updating FETCH_HEAD.

We've been using this step as a critical background job in Scalar
[1] (and VFS for Git). This solved a pain point that was showing up
in user reports: fetching was a pain! Users do not like waiting to
download the data that was created while they were away from their
machines. After implementing background fetch, the foreground fetch
commands sped up significantly because they mostly just update refs
and download a small amount of new data. The effect is especially
dramatic when paried with --no-show-forced-udpates (through
fetch.showForcedUpdates=false).

[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/FetchStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 15 +++++++++
 builtin/gc.c                      | 52 +++++++++++++++++++++++++++++++
 t/t7900-maintenance.sh            | 25 +++++++++++++++
 3 files changed, 92 insertions(+)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index e1a2a8902c..bb0d5eded4 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -57,6 +57,21 @@ since it will not expire `.graph` files that were in the previous
 `commit-graph-chain` file. They will be deleted by a later run based on
 the expiration delay.
 
+prefetch::
+	The `prefetch` task updates the object directory with the latest
+	objects from all registered remotes. For each remote, a `git fetch`
+	command is run. The refmap is custom to avoid updating local or remote
+	branches (those in `refs/heads` or `refs/remotes`). Instead, the
+	remote refs are stored in `refs/prefetch/<remote>/`. Also, tags are
+	not updated.
++
+This is done to avoid disrupting the remote-tracking branches. The end users
+expect these refs to stay unmoved unless they initiate a fetch.  With prefetch
+task, however, the objects necessary to complete a later real fetch would
+already be obtained, so the real fetch would go faster.  In the ideal case,
+it will just become an update to bunch of remote-tracking branches without
+any object transfer.
+
 gc::
 	Cleanup unnecessary files and optimize the local repository. "GC"
 	stands for "garbage collection," but this task performs many
diff --git a/builtin/gc.c b/builtin/gc.c
index 8162bca974..942b7ea535 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -29,6 +29,7 @@
 #include "tree.h"
 #include "promisor-remote.h"
 #include "refs.h"
+#include "remote.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -843,6 +844,52 @@ static int maintenance_task_commit_graph(struct maintenance_opts *opts)
 	return 1;
 }
 
+static int fetch_remote(const char *remote, struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "fetch", remote, "--prune", "--no-tags",
+		     "--no-write-fetch-head", "--refmap=", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--quiet");
+
+	strvec_pushf(&child.args, "+refs/heads/*:refs/prefetch/%s/*", remote);
+
+	return !!run_command(&child);
+}
+
+static int fill_each_remote(struct remote *remote, void *cbdata)
+{
+	struct string_list *remotes = (struct string_list *)cbdata;
+
+	string_list_append(remotes, remote->name);
+	return 0;
+}
+
+static int maintenance_task_prefetch(struct maintenance_opts *opts)
+{
+	int result = 0;
+	struct string_list_item *item;
+	struct string_list remotes = STRING_LIST_INIT_DUP;
+
+	if (for_each_remote(fill_each_remote, &remotes)) {
+		error(_("failed to fill remotes"));
+		result = 1;
+		goto cleanup;
+	}
+
+	for (item = remotes.items;
+	     item && item < remotes.items + remotes.nr;
+	     item++)
+		result |= fetch_remote(item->string, opts);
+
+cleanup:
+	string_list_clear(&remotes, 0);
+	return result;
+}
+
 static int maintenance_task_gc(struct maintenance_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -880,6 +927,7 @@ struct maintenance_task {
 };
 
 enum maintenance_task_label {
+	TASK_PREFETCH,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -888,6 +936,10 @@ enum maintenance_task_label {
 };
 
 static struct maintenance_task tasks[] = {
+	[TASK_PREFETCH] = {
+		"prefetch",
+		maintenance_task_prefetch,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 406dc7c303..3dd99ef660 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -58,4 +58,29 @@ test_expect_success 'run --task duplicate' '
 	test_i18ngrep "cannot be selected multiple times" err
 '
 
+test_expect_success 'run --task=prefetch with no remotes' '
+	git maintenance run --task=prefetch 2>err &&
+	test_must_be_empty err
+'
+
+test_expect_success 'prefetch multiple remotes' '
+	git clone . clone1 &&
+	git clone . clone2 &&
+	git remote add remote1 "file://$(pwd)/clone1" &&
+	git remote add remote2 "file://$(pwd)/clone2" &&
+	git -C clone1 switch -c one &&
+	git -C clone2 switch -c two &&
+	test_commit -C clone1 one &&
+	test_commit -C clone2 two &&
+	GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null &&
+	fetchargs="--prune --no-tags --no-write-fetch-head --refmap= --quiet" &&
+	test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\* <run-prefetch.txt &&
+	test_subcommand git fetch remote2 $fetchargs +refs/heads/\\*:refs/prefetch/remote2/\\* <run-prefetch.txt &&
+	test_path_is_missing .git/refs/remotes &&
+	test_cmp clone1/.git/refs/heads/one .git/refs/prefetch/remote1/one &&
+	test_cmp clone2/.git/refs/heads/two .git/refs/prefetch/remote2/two &&
+	git log prefetch/remote1/one &&
+	git log prefetch/remote2/two
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH 3/9] maintenance: add loose-objects task
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  2020-08-06 16:30 ` [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
  2020-08-06 16:30 ` [PATCH 2/9] maintenance: add prefetch task Derrick Stolee via GitGitGadget
@ 2020-08-06 16:30 ` Derrick Stolee via GitGitGadget
  2020-08-12 23:10   ` Emily Shaffer
  2020-08-06 16:30 ` [PATCH 4/9] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
                   ` (6 subsequent siblings)
  9 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

One goal of background maintenance jobs is to allow a user to
disable auto-gc (gc.auto=0) but keep their repository in a clean
state. Without any cleanup, loose objects will clutter the object
database and slow operations. In addition, the loose objects will
take up extra space because they are not stored with deltas against
similar objects.

Create a 'loose-objects' task for the 'git maintenance run' command.
This helps clean up loose objects without disrupting concurrent Git
commands using the following sequence of events:

1. Run 'git prune-packed' to delete any loose objects that exist
   in a pack-file. Concurrent commands will prefer the packed
   version of the object to the loose version. (Of course, there
   are exceptions for commands that specifically care about the
   location of an object. These are rare for a user to run on
   purpose, and we hope a user that has selected background
   maintenance will not be trying to do foreground maintenance.)

2. Run 'git pack-objects' on a batch of loose objects. These
   objects are grouped by scanning the loose object directories in
   lexicographic order until listing all loose objects -or-
   reaching 50,000 objects. This is more than enough if the loose
   objects are created only by a user doing normal development.
   We noticed users with _millions_ of loose objects because VFS
   for Git downloads blobs on-demand when a file read operation
   requires populating a virtual file. This has potential of
   happening in partial clones if someone runs 'git grep' or
   otherwise evades the batch-download feature for requesting
   promisor objects.

This step is based on a similar step in Scalar [1] and VFS for Git.
[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/LooseObjectsStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 11 ++++
 builtin/gc.c                      | 97 +++++++++++++++++++++++++++++++
 t/t7900-maintenance.sh            | 39 +++++++++++++
 3 files changed, 147 insertions(+)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index bb0d5eded4..898aff4726 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -80,6 +80,17 @@ gc::
 	It can also be disruptive in some situations, as it deletes stale
 	data.
 
+loose-objects::
+	The `loose-objects` job cleans up loose objects and places them into
+	pack-files. In order to prevent race conditions with concurrent Git
+	commands, it follows a two-step process. First, it deletes any loose
+	objects that already exist in a pack-file; concurrent Git processes
+	will examine the pack-file for the object data instead of the loose
+	object. Second, it creates a new pack-file (starting with "loose-")
+	containing a batch of loose objects. The batch size is limited to 50
+	thousand objects to prevent the job from taking too long on a
+	repository with many loose objects.
+
 OPTIONS
 -------
 --auto::
diff --git a/builtin/gc.c b/builtin/gc.c
index 942b7ea535..60261d2647 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -908,6 +908,98 @@ static int maintenance_task_gc(struct maintenance_opts *opts)
 	return run_command(&child);
 }
 
+static int prune_packed(struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_push(&child.args, "prune-packed");
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--quiet");
+
+	return !!run_command(&child);
+}
+
+struct write_loose_object_data {
+	FILE *in;
+	int count;
+	int batch_size;
+};
+
+static int bail_on_loose(const struct object_id *oid,
+			 const char *path,
+			 void *data)
+{
+	return 1;
+}
+
+static int write_loose_object_to_stdin(const struct object_id *oid,
+				       const char *path,
+				       void *data)
+{
+	struct write_loose_object_data *d = (struct write_loose_object_data *)data;
+
+	fprintf(d->in, "%s\n", oid_to_hex(oid));
+
+	return ++(d->count) > d->batch_size;
+}
+
+static int pack_loose(struct maintenance_opts *opts)
+{
+	struct repository *r = the_repository;
+	int result = 0;
+	struct write_loose_object_data data;
+	struct child_process pack_proc = CHILD_PROCESS_INIT;
+
+	/*
+	 * Do not start pack-objects process
+	 * if there are no loose objects.
+	 */
+	if (!for_each_loose_file_in_objdir(r->objects->odb->path,
+					   bail_on_loose,
+					   NULL, NULL, NULL))
+		return 0;
+
+	pack_proc.git_cmd = 1;
+
+	strvec_push(&pack_proc.args, "pack-objects");
+	if (opts->quiet)
+		strvec_push(&pack_proc.args, "--quiet");
+	strvec_pushf(&pack_proc.args, "%s/pack/loose", r->objects->odb->path);
+
+	pack_proc.in = -1;
+
+	if (start_command(&pack_proc)) {
+		error(_("failed to start 'git pack-objects' process"));
+		return 1;
+	}
+
+	data.in = xfdopen(pack_proc.in, "w");
+	data.count = 0;
+	data.batch_size = 50000;
+
+	for_each_loose_file_in_objdir(r->objects->odb->path,
+				      write_loose_object_to_stdin,
+				      NULL,
+				      NULL,
+				      &data);
+
+	fclose(data.in);
+
+	if (finish_command(&pack_proc)) {
+		error(_("failed to finish 'git pack-objects' process"));
+		result = 1;
+	}
+
+	return result;
+}
+
+static int maintenance_task_loose_objects(struct maintenance_opts *opts)
+{
+	return prune_packed(opts) || pack_loose(opts);
+}
+
 typedef int maintenance_task_fn(struct maintenance_opts *opts);
 
 /*
@@ -928,6 +1020,7 @@ struct maintenance_task {
 
 enum maintenance_task_label {
 	TASK_PREFETCH,
+	TASK_LOOSE_OBJECTS,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -940,6 +1033,10 @@ static struct maintenance_task tasks[] = {
 		"prefetch",
 		maintenance_task_prefetch,
 	},
+	[TASK_LOOSE_OBJECTS] = {
+		"loose-objects",
+		maintenance_task_loose_objects,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 3dd99ef660..8d54f93a10 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -83,4 +83,43 @@ test_expect_success 'prefetch multiple remotes' '
 	git log prefetch/remote2/two
 '
 
+test_expect_success 'loose-objects task' '
+	# Repack everything so we know the state of the object dir
+	git repack -adk &&
+
+	# Hack to stop maintenance from running during "git commit"
+	echo in use >.git/objects/maintenance.lock &&
+
+	# Assuming that "git commit" creates at least one loose object
+	test_commit create-loose-object &&
+	rm .git/objects/maintenance.lock &&
+
+	ls .git/objects >obj-dir-before &&
+	test_file_not_empty obj-dir-before &&
+	ls .git/objects/pack/*.pack >packs-before &&
+	test_line_count = 1 packs-before &&
+
+	# The first run creates a pack-file
+	# but does not delete loose objects.
+	git maintenance run --task=loose-objects &&
+	ls .git/objects >obj-dir-between &&
+	test_cmp obj-dir-before obj-dir-between &&
+	ls .git/objects/pack/*.pack >packs-between &&
+	test_line_count = 2 packs-between &&
+	ls .git/objects/pack/loose-*.pack >loose-packs &&
+	test_line_count = 1 loose-packs &&
+
+	# The second run deletes loose objects
+	# but does not create a pack-file.
+	git maintenance run --task=loose-objects &&
+	ls .git/objects >obj-dir-after &&
+	cat >expect <<-\EOF &&
+	info
+	pack
+	EOF
+	test_cmp expect obj-dir-after &&
+	ls .git/objects/pack/*.pack >packs-after &&
+	test_cmp packs-between packs-after
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH 4/9] maintenance: create auto condition for loose-objects
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                   ` (2 preceding siblings ...)
  2020-08-06 16:30 ` [PATCH 3/9] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
@ 2020-08-06 16:30 ` Derrick Stolee via GitGitGadget
  2020-08-06 16:30 ` [PATCH 5/9] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
                   ` (5 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The loose-objects task deletes loose objects that already exist in a
pack-file, then place the remaining loose objects into a new pack-file.
If this step runs all the time, then we risk creating pack-files with
very few objects with every 'git commit' process. To prevent
overwhelming the packs directory with small pack-files, place a minimum
number of objects to justify the task.

The 'maintenance.loose-objects.auto' config option specifies a minimum
number of loose objects to justify the task to run under the '--auto'
option. This defaults to 100 loose objects. Setting the value to zero
will prevent the step from running under '--auto' while a negative value
will force it to run every time.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/maintenance.txt |  9 +++++++++
 builtin/gc.c                         | 30 ++++++++++++++++++++++++++++
 t/t7900-maintenance.sh               | 25 +++++++++++++++++++++++
 3 files changed, 64 insertions(+)

diff --git a/Documentation/config/maintenance.txt b/Documentation/config/maintenance.txt
index 9bd69b9df3..a9442dd260 100644
--- a/Documentation/config/maintenance.txt
+++ b/Documentation/config/maintenance.txt
@@ -12,3 +12,12 @@ maintenance.commit-graph.auto::
 	reachable commits that are not in the commit-graph file is at least
 	the value of `maintenance.commit-graph.auto`. The default value is
 	100.
+
+maintenance.loose-objects.auto::
+	This integer config option controls how often the `loose-objects` task
+	should be run as part of `git maintenance run --auto`. If zero, then
+	the `loose-objects` task will not run with the `--auto` option. A
+	negative value will force the task to run every time. Otherwise, a
+	positive value implies the command should run when the number of
+	loose objects is at least the value of `maintenance.loose-objects.auto`.
+	The default value is 100.
diff --git a/builtin/gc.c b/builtin/gc.c
index 60261d2647..23329b5652 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -927,6 +927,35 @@ struct write_loose_object_data {
 	int batch_size;
 };
 
+static int loose_object_auto_limit = 100;
+
+static int loose_object_count(const struct object_id *oid,
+			       const char *path,
+			       void *data)
+{
+	int *count = (int*)data;
+	if (++(*count) >= loose_object_auto_limit)
+		return 1;
+	return 0;
+}
+
+static int loose_object_auto_condition(void)
+{
+	int count = 0;
+
+	git_config_get_int("maintenance.loose-objects.auto",
+			   &loose_object_auto_limit);
+
+	if (!loose_object_auto_limit)
+		return 0;
+	if (loose_object_auto_limit < 0)
+		return 1;
+
+	return for_each_loose_file_in_objdir(the_repository->objects->odb->path,
+					     loose_object_count,
+					     NULL, NULL, &count);
+}
+
 static int bail_on_loose(const struct object_id *oid,
 			 const char *path,
 			 void *data)
@@ -1036,6 +1065,7 @@ static struct maintenance_task tasks[] = {
 	[TASK_LOOSE_OBJECTS] = {
 		"loose-objects",
 		maintenance_task_loose_objects,
+		loose_object_auto_condition,
 	},
 	[TASK_GC] = {
 		"gc",
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 8d54f93a10..71ac686c09 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -122,4 +122,29 @@ test_expect_success 'loose-objects task' '
 	test_cmp packs-between packs-after
 '
 
+test_expect_success 'maintenance.loose-objects.auto' '
+	git repack -adk &&
+	GIT_TRACE2_EVENT="$(pwd)/trace-lo1.txt" \
+		git -c maintenance.loose-objects.auto=1 maintenance \
+		run --auto --task=loose-objects 2>/dev/null &&
+	test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
+	for i in 1 2
+	do
+		printf data-A-$i | git hash-object -t blob --stdin -w &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-loA-$i" \
+			git -c maintenance.loose-objects.auto=2 \
+			maintenance run --auto --task=loose-objects 2>/dev/null &&
+		test_subcommand ! git prune-packed --quiet <trace-loA-$i &&
+		printf data-B-$i | git hash-object -t blob --stdin -w &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-loB-$i" \
+			git -c maintenance.loose-objects.auto=2 \
+			maintenance run --auto --task=loose-objects 2>/dev/null &&
+		test_subcommand git prune-packed --quiet <trace-loB-$i &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-loC-$i" \
+			git -c maintenance.loose-objects.auto=2 \
+			maintenance run --auto --task=loose-objects 2>/dev/null &&
+		test_subcommand git prune-packed --quiet <trace-loC-$i || return 1
+	done
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH 5/9] midx: enable core.multiPackIndex by default
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                   ` (3 preceding siblings ...)
  2020-08-06 16:30 ` [PATCH 4/9] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
@ 2020-08-06 16:30 ` Derrick Stolee via GitGitGadget
  2020-08-06 16:30 ` [PATCH 6/9] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
                   ` (4 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The core.multiPackIndex setting has been around since c4d25228ebb
(config: create core.multiPackIndex setting, 2018-07-12), but has been
disabled by default. If a user wishes to use the multi-pack-index
feature, then they must enable this config and run 'git multi-pack-index
write'.

The multi-pack-index feature is relatively stable now, so make the
config option true by default. For users that do not use a
multi-pack-index, the only extra cost will be a file lookup to see if a
multi-pack-index file exists (once per process, per object directory).

Also, this config option will be referenced by an upcoming
"incremental-repack" task in the maintenance builtin, so move the config
option into the repository settings struct. Note that if
GIT_TEST_MULTI_PACK_INDEX=1, then we want to ignore the config option
and treat core.multiPackIndex as enabled.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/core.txt |  4 ++--
 midx.c                        | 11 +++--------
 repo-settings.c               |  6 ++++++
 repository.h                  |  2 ++
 4 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 74619a9c03..86c91d5381 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -606,8 +606,8 @@ core.useReplaceRefs::
 
 core.multiPackIndex::
 	Use the multi-pack-index file to track multiple packfiles using a
-	single index. See link:technical/multi-pack-index.html[the
-	multi-pack-index design document].
+	single index. See linkgit:git-multi-pack-index[1] for more
+	information. Defaults to true.
 
 core.sparseCheckout::
 	Enable "sparse checkout" feature. See linkgit:git-sparse-checkout[1]
diff --git a/midx.c b/midx.c
index a5fb797ede..ef499cf504 100644
--- a/midx.c
+++ b/midx.c
@@ -10,6 +10,7 @@
 #include "progress.h"
 #include "trace2.h"
 #include "run-command.h"
+#include "repository.h"
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
@@ -384,15 +385,9 @@ int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, i
 {
 	struct multi_pack_index *m;
 	struct multi_pack_index *m_search;
-	int config_value;
-	static int env_value = -1;
 
-	if (env_value < 0)
-		env_value = git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0);
-
-	if (!env_value &&
-	    (repo_config_get_bool(r, "core.multipackindex", &config_value) ||
-	    !config_value))
+	prepare_repo_settings(r);
+	if (!r->settings.core_multi_pack_index)
 		return 0;
 
 	for (m_search = r->objects->multi_pack_index; m_search; m_search = m_search->next)
diff --git a/repo-settings.c b/repo-settings.c
index 0918408b34..5bd2c22726 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -1,6 +1,7 @@
 #include "cache.h"
 #include "config.h"
 #include "repository.h"
+#include "midx.h"
 
 #define UPDATE_DEFAULT_BOOL(s,v) do { if (s == -1) { s = v; } } while(0)
 
@@ -47,6 +48,11 @@ void prepare_repo_settings(struct repository *r)
 		r->settings.pack_use_sparse = value;
 	UPDATE_DEFAULT_BOOL(r->settings.pack_use_sparse, 1);
 
+	value = git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0);
+	if (value || !repo_config_get_bool(r, "core.multipackindex", &value))
+		r->settings.core_multi_pack_index = value;
+	UPDATE_DEFAULT_BOOL(r->settings.core_multi_pack_index, 1);
+
 	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
 		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
diff --git a/repository.h b/repository.h
index 3c1f7d54bd..3901ce0b65 100644
--- a/repository.h
+++ b/repository.h
@@ -37,6 +37,8 @@ struct repo_settings {
 
 	int pack_use_sparse;
 	enum fetch_negotiation_setting fetch_negotiation_algorithm;
+
+	int core_multi_pack_index;
 };
 
 struct repository {
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH 6/9] midx: use start_delayed_progress()
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                   ` (4 preceding siblings ...)
  2020-08-06 16:30 ` [PATCH 5/9] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
@ 2020-08-06 16:30 ` Derrick Stolee via GitGitGadget
  2020-08-06 16:30 ` [PATCH 7/9] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
                   ` (3 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

Now that the multi-pack-index may be written as part of auto maintenance
at the end of a command, reduce the progress output when the operations
are quick. Use start_delayed_progress() instead of start_progress().

Update t5319-multi-pack-index.sh to use GIT_PROGRESS_DELAY=0 now that
the progress indicators are conditional.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 midx.c                      | 10 +++++-----
 t/t5319-multi-pack-index.sh | 14 +++++++-------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/midx.c b/midx.c
index ef499cf504..aa37d5da86 100644
--- a/midx.c
+++ b/midx.c
@@ -832,7 +832,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 
 	packs.pack_paths_checked = 0;
 	if (flags & MIDX_PROGRESS)
-		packs.progress = start_progress(_("Adding packfiles to multi-pack-index"), 0);
+		packs.progress = start_delayed_progress(_("Adding packfiles to multi-pack-index"), 0);
 	else
 		packs.progress = NULL;
 
@@ -969,7 +969,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 	}
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Writing chunks to multi-pack-index"),
+		progress = start_delayed_progress(_("Writing chunks to multi-pack-index"),
 					  num_chunks);
 	for (i = 0; i < num_chunks; i++) {
 		if (written != chunk_offsets[i])
@@ -1104,7 +1104,7 @@ int verify_midx_file(struct repository *r, const char *object_dir, unsigned flag
 		return 0;
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Looking for referenced packfiles"),
+		progress = start_delayed_progress(_("Looking for referenced packfiles"),
 					  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
 		if (prepare_midx_pack(r, m, i))
@@ -1225,7 +1225,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 	count = xcalloc(m->num_packs, sizeof(uint32_t));
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Counting referenced objects"),
+		progress = start_delayed_progress(_("Counting referenced objects"),
 					  m->num_objects);
 	for (i = 0; i < m->num_objects; i++) {
 		int pack_int_id = nth_midxed_pack_int_id(m, i);
@@ -1235,7 +1235,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 	stop_progress(&progress);
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Finding and deleting unreferenced packfiles"),
+		progress = start_delayed_progress(_("Finding and deleting unreferenced packfiles"),
 					  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
 		char *pack_name;
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 7214cab36c..12f41dfc18 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -172,12 +172,12 @@ test_expect_success 'write progress off for redirected stderr' '
 '
 
 test_expect_success 'write force progress on for stderr' '
-	git multi-pack-index --object-dir=$objdir --progress write 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --progress write 2>err &&
 	test_file_not_empty err
 '
 
 test_expect_success 'write with the --no-progress option' '
-	git multi-pack-index --object-dir=$objdir --no-progress write 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --no-progress write 2>err &&
 	test_line_count = 0 err
 '
 
@@ -334,17 +334,17 @@ test_expect_success 'git-fsck incorrect offset' '
 '
 
 test_expect_success 'repack progress off for redirected stderr' '
-	git multi-pack-index --object-dir=$objdir repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir repack 2>err &&
 	test_line_count = 0 err
 '
 
 test_expect_success 'repack force progress on for stderr' '
-	git multi-pack-index --object-dir=$objdir --progress repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --progress repack 2>err &&
 	test_file_not_empty err
 '
 
 test_expect_success 'repack with the --no-progress option' '
-	git multi-pack-index --object-dir=$objdir --no-progress repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --no-progress repack 2>err &&
 	test_line_count = 0 err
 '
 
@@ -488,7 +488,7 @@ test_expect_success 'expire progress off for redirected stderr' '
 test_expect_success 'expire force progress on for stderr' '
 	(
 		cd dup &&
-		git multi-pack-index --progress expire 2>err &&
+		GIT_PROGRESS_DELAY=0 git multi-pack-index --progress expire 2>err &&
 		test_file_not_empty err
 	)
 '
@@ -496,7 +496,7 @@ test_expect_success 'expire force progress on for stderr' '
 test_expect_success 'expire with the --no-progress option' '
 	(
 		cd dup &&
-		git multi-pack-index --no-progress expire 2>err &&
+		GIT_PROGRESS_DELAY=0 git multi-pack-index --no-progress expire 2>err &&
 		test_line_count = 0 err
 	)
 '
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH 7/9] maintenance: add incremental-repack task
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                   ` (5 preceding siblings ...)
  2020-08-06 16:30 ` [PATCH 6/9] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
@ 2020-08-06 16:30 ` Derrick Stolee via GitGitGadget
  2020-08-06 16:30 ` [PATCH 8/9] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
                   ` (2 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The previous change cleaned up loose objects using the
'loose-objects' that can be run safely in the background. Add a
similar job that performs similar cleanups for pack-files.

One issue with running 'git repack' is that it is designed to
repack all pack-files into a single pack-file. While this is the
most space-efficient way to store object data, it is not time or
memory efficient. This becomes extremely important if the repo is
so large that a user struggles to store two copies of the pack on
their disk.

Instead, perform an "incremental" repack by collecting a few small
pack-files into a new pack-file. The multi-pack-index facilitates
this process ever since 'git multi-pack-index expire' was added in
19575c7 (multi-pack-index: implement 'expire' subcommand,
2019-06-10) and 'git multi-pack-index repack' was added in ce1e4a1
(midx: implement midx_repack(), 2019-06-10).

The 'incremental-repack' task runs the following steps:

1. 'git multi-pack-index write' creates a multi-pack-index file if
   one did not exist, and otherwise will update the multi-pack-index
   with any new pack-files that appeared since the last write. This
   is particularly relevant with the background fetch job.

   When the multi-pack-index sees two copies of the same object, it
   stores the offset data into the newer pack-file. This means that
   some old pack-files could become "unreferenced" which I will use
   to mean "a pack-file that is in the pack-file list of the
   multi-pack-index but none of the objects in the multi-pack-index
   reference a location inside that pack-file."

2. 'git multi-pack-index expire' deletes any unreferenced pack-files
   and updaes the multi-pack-index to drop those pack-files from the
   list. This is safe to do as concurrent Git processes will see the
   multi-pack-index and not open those packs when looking for object
   contents. (Similar to the 'loose-objects' job, there are some Git
   commands that open pack-files regardless of the multi-pack-index,
   but they are rarely used. Further, a user that self-selects to
   use background operations would likely refrain from using those
   commands.)

3. 'git multi-pack-index repack --bacth-size=<size>' collects a set
   of pack-files that are listed in the multi-pack-index and creates
   a new pack-file containing the objects whose offsets are listed
   by the multi-pack-index to be in those objects. The set of pack-
   files is selected greedily by sorting the pack-files by modified
   time and adding a pack-file to the set if its "expected size" is
   smaller than the batch size until the total expected size of the
   selected pack-files is at least the batch size. The "expected
   size" is calculated by taking the size of the pack-file divided
   by the number of objects in the pack-file and multiplied by the
   number of objects from the multi-pack-index with offset in that
   pack-file. The expected size approximates how much data from that
   pack-file will contribute to the resulting pack-file size. The
   intention is that the resulting pack-file will be close in size
   to the provided batch size.

   The next run of the incremental-repack task will delete these
   repacked pack-files during the 'expire' step.

   In this version, the batch size is set to "0" which ignores the
   size restrictions when selecting the pack-files. It instead
   selects all pack-files and repacks all packed objects into a
   single pack-file. This will be updated in the next change, but
   it requires doing some calculations that are better isolated to
   a separate change.

Each of the above steps update the multi-pack-index file. After
each step, we verify the new multi-pack-index. If the new
multi-pack-index is corrupt, then delete the multi-pack-index,
rewrite it from scratch, and stop doing the later steps of the
job. This is intended to be an extra-safe check without leaving
a repo with many pack-files without a multi-pack-index.

These steps are based on a similar background maintenance step in
Scalar (and VFS for Git) [1]. This was incredibly effective for
users of the Windows OS repository. After using the same VFS for Git
repository for over a year, some users had _thousands_ of pack-files
that combined to up to 250 GB of data. We noticed a few users were
running into the open file descriptor limits (due in part to a bug
in the multi-pack-index fixed by af96fe3 (midx: add packs to
packed_git linked list, 2019-04-29).

These pack-files were mostly small since they contained the commits
and trees that were pushed to the origin in a given hour. The GVFS
protocol includes a "prefetch" step that asks for pre-computed pack-
files containing commits and trees by timestamp. These pack-files
were grouped into "daily" pack-files once a day for up to 30 days.
If a user did not request prefetch packs for over 30 days, then they
would get the entire history of commits and trees in a new, large
pack-file. This led to a large number of pack-files that had poor
delta compression.

By running this pack-file maintenance step once per day, these repos
with thousands of packs spanning 200+ GB dropped to dozens of pack-
files spanning 30-50 GB. This was done all without removing objects
from the system and using a constant batch size of two gigabytes.
Once the work was done to reduce the pack-files to small sizes, the
batch size of two gigabytes means that not every run triggers a
repack operation, so the following run will not expire a pack-file.
This has kept these repos in a "clean" state.

[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/PackfileMaintenanceStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt |  15 ++++
 builtin/gc.c                      | 113 ++++++++++++++++++++++++++++++
 midx.c                            |   2 +-
 midx.h                            |   1 +
 t/t5319-multi-pack-index.sh       |   1 +
 t/t7900-maintenance.sh            |  38 ++++++++++
 6 files changed, 169 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 898aff4726..1bd105918f 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -91,6 +91,21 @@ loose-objects::
 	thousand objects to prevent the job from taking too long on a
 	repository with many loose objects.
 
+incremental-repack::
+	The `incremental-repack` job repacks the object directory
+	using the `multi-pack-index` feature. In order to prevent race
+	conditions with concurrent Git commands, it follows a two-step
+	process. First, it deletes any pack-files included in the
+	`multi-pack-index` where none of the objects in the
+	`multi-pack-index` reference those pack-files; this only happens
+	if all objects in the pack-file are also stored in a newer
+	pack-file. Second, it selects a group of pack-files whose "expected
+	size" is below the batch size until the group has total expected
+	size at least the batch size; see the `--batch-size` option for
+	the `repack` subcommand in linkgit:git-multi-pack-index[1]. The
+	default batch-size is zero, which is a special case that attempts
+	to repack all pack-files into a single pack-file.
+
 OPTIONS
 -------
 --auto::
diff --git a/builtin/gc.c b/builtin/gc.c
index 23329b5652..35c6d7ce82 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -30,6 +30,7 @@
 #include "promisor-remote.h"
 #include "refs.h"
 #include "remote.h"
+#include "midx.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -1029,6 +1030,113 @@ static int maintenance_task_loose_objects(struct maintenance_opts *opts)
 	return prune_packed(opts) || pack_loose(opts);
 }
 
+static int multi_pack_index_write(struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "write", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	if (run_command(&child))
+		return error(_("failed to write multi-pack-index"));
+
+	return 0;
+}
+
+static int rewrite_multi_pack_index(struct maintenance_opts *opts)
+{
+	struct repository *r = the_repository;
+	char *midx_name = get_midx_filename(r->objects->odb->path);
+
+	unlink(midx_name);
+	free(midx_name);
+
+	return multi_pack_index_write(opts);
+}
+
+static int multi_pack_index_verify(struct maintenance_opts *opts,
+				   const char *message)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "verify", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	if (run_command(&child)) {
+		warning(_("'git multi-pack-index verify' failed %s"), message);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int multi_pack_index_expire(struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "expire", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	close_object_store(the_repository->objects);
+
+	if (run_command(&child))
+		return error(_("'git multi-pack-index expire' failed"));
+
+	return 0;
+}
+
+static int multi_pack_index_repack(struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "repack", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	strvec_push(&child.args, "--batch-size=0");
+
+	close_object_store(the_repository->objects);
+
+	if (run_command(&child))
+		return error(_("'git multi-pack-index repack' failed"));
+
+	return 0;
+}
+
+static int maintenance_task_incremental_repack(struct maintenance_opts *opts)
+{
+	prepare_repo_settings(the_repository);
+	if (!the_repository->settings.core_multi_pack_index) {
+		warning(_("skipping incremental-repack task because core.multiPackIndex is disabled"));
+		return 0;
+	}
+
+	if (multi_pack_index_write(opts))
+		return 1;
+	if (multi_pack_index_verify(opts, "after initial write"))
+		return rewrite_multi_pack_index(opts);
+	if (multi_pack_index_expire(opts))
+		return 1;
+	if (multi_pack_index_verify(opts, "after expire step"))
+		return !!rewrite_multi_pack_index(opts);
+	if (multi_pack_index_repack(opts))
+		return 1;
+	if (multi_pack_index_verify(opts, "after repack step"))
+		return !!rewrite_multi_pack_index(opts);
+	return 0;
+}
+
 typedef int maintenance_task_fn(struct maintenance_opts *opts);
 
 /*
@@ -1050,6 +1158,7 @@ struct maintenance_task {
 enum maintenance_task_label {
 	TASK_PREFETCH,
 	TASK_LOOSE_OBJECTS,
+	TASK_INCREMENTAL_REPACK,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -1067,6 +1176,10 @@ static struct maintenance_task tasks[] = {
 		maintenance_task_loose_objects,
 		loose_object_auto_condition,
 	},
+	[TASK_INCREMENTAL_REPACK] = {
+		"incremental-repack",
+		maintenance_task_incremental_repack,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/midx.c b/midx.c
index aa37d5da86..66d7053d83 100644
--- a/midx.c
+++ b/midx.c
@@ -37,7 +37,7 @@
 
 #define PACK_EXPIRED UINT_MAX
 
-static char *get_midx_filename(const char *object_dir)
+char *get_midx_filename(const char *object_dir)
 {
 	return xstrfmt("%s/pack/multi-pack-index", object_dir);
 }
diff --git a/midx.h b/midx.h
index b18cf53bc4..baeecc70c9 100644
--- a/midx.h
+++ b/midx.h
@@ -37,6 +37,7 @@ struct multi_pack_index {
 
 #define MIDX_PROGRESS     (1 << 0)
 
+char *get_midx_filename(const char *object_dir);
 struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local);
 int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
 int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result);
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 12f41dfc18..26f224b0e3 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -3,6 +3,7 @@
 test_description='multi-pack-indexes'
 . ./test-lib.sh
 
+GIT_TEST_MULTI_PACK_INDEX=0
 objdir=.git/objects
 
 midx_read_expect () {
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 71ac686c09..be19ac7623 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -5,6 +5,7 @@ test_description='git maintenance builtin'
 . ./test-lib.sh
 
 GIT_TEST_COMMIT_GRAPH=0
+GIT_TEST_MULTI_PACK_INDEX=0
 
 test_expect_success 'help text' '
 	test_expect_code 129 git maintenance -h 2>err &&
@@ -147,4 +148,41 @@ test_expect_success 'maintenance.loose-objects.auto' '
 	done
 '
 
+test_expect_success 'incremental-repack task' '
+	packDir=.git/objects/pack &&
+	for i in $(test_seq 1 5)
+	do
+		test_commit $i || return 1
+	done &&
+
+	# Create three disjoint pack-files with size BIG, small, small.
+	echo HEAD~2 | git pack-objects --revs $packDir/test-1 &&
+	test_tick &&
+	git pack-objects --revs $packDir/test-2 <<-\EOF &&
+	HEAD~1
+	^HEAD~2
+	EOF
+	test_tick &&
+	git pack-objects --revs $packDir/test-3 <<-\EOF &&
+	HEAD
+	^HEAD~1
+	EOF
+	rm -f $packDir/pack-* &&
+	rm -f $packDir/loose-* &&
+	ls $packDir/*.pack >packs-before &&
+	test_line_count = 3 packs-before &&
+
+	# the job repacks the two into a new pack, but does not
+	# delete the old ones.
+	git maintenance run --task=incremental-repack &&
+	ls $packDir/*.pack >packs-between &&
+	test_line_count = 4 packs-between &&
+
+	# the job deletes the two old packs, and does not write
+	# a new one because only one pack remains.
+	git maintenance run --task=incremental-repack &&
+	ls .git/objects/pack/*.pack >packs-after &&
+	test_line_count = 1 packs-after
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH 8/9] maintenance: auto-size incremental-repack batch
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                   ` (6 preceding siblings ...)
  2020-08-06 16:30 ` [PATCH 7/9] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
@ 2020-08-06 16:30 ` Derrick Stolee via GitGitGadget
  2020-08-06 17:02   ` Son Luong Ngoc
  2020-08-06 16:30 ` [PATCH 9/9] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  9 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

When repacking during the 'incremental-repack' task, we use the
--batch-size option in 'git multi-pack-index repack'. The initial setting
used --batch-size=0 to repack everything into a single pack-file. This is
not sustainable for a large repository. The amount of work required is
also likely to use too many system resources for a background job.

Update the 'incremental-repack' task by dynamically computing a
--batch-size option based on the current pack-file structure.

The dynamic default size is computed with this idea in mind for a client
repository that was cloned from a very large remote: there is likely one
"big" pack-file that was created at clone time. Thus, do not try
repacking it as it is likely packed efficiently by the server.

Instead, we select the second-largest pack-file, and create a batch size
that is one larger than that pack-file. If there are three or more
pack-files, then this guarantees that at least two will be combined into
a new pack-file.

Of course, this means that the second-largest pack-file size is likely
to grow over time and may eventually surpass the initially-cloned
pack-file. Recall that the pack-file batch is selected in a greedy
manner: the packs are considered from oldest to newest and are selected
if they have size smaller than the batch size until the total selected
size is larger than the batch size. Thus, that oldest "clone" pack will
be first to repack after the new data creates a pack larger than that.

We also want to place some limits on how large these pack-files become,
in order to bound the amount of time spent repacking. A maximum
batch-size of two gigabytes means that large repositories will never be
packed into a single pack-file using this job, but also that repack is
rather expensive. This is a trade-off that is valuable to have if the
maintenance is being run automatically or in the background. Users who
truly want to optimize for space and performance (and are willing to pay
the upfront cost of a full repack) can use the 'gc' task to do so.

Create a test for this two gigabyte limit by creating an EXPENSIVE test
that generates two pack-files of roughly 2.5 gigabytes in size, then
performs an incremental repack. Check that the --batch-size argument in
the subcommand uses the hard-coded maximum.

Helped-by: Chris Torek <chris.torek@gmail.com>
Reported-by: Son Luong Ngoc <sluongng@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 builtin/gc.c           | 43 +++++++++++++++++++++++++++++++++++++++++-
 t/t7900-maintenance.sh | 36 +++++++++++++++++++++++++++++++++--
 2 files changed, 76 insertions(+), 3 deletions(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 35c6d7ce82..c09bc1381c 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1094,6 +1094,46 @@ static int multi_pack_index_expire(struct maintenance_opts *opts)
 	return 0;
 }
 
+#define TWO_GIGABYTES (INT32_MAX)
+
+static off_t get_auto_pack_size(void)
+{
+	/*
+	 * The "auto" value is special: we optimize for
+	 * one large pack-file (i.e. from a clone) and
+	 * expect the rest to be small and they can be
+	 * repacked quickly.
+	 *
+	 * The strategy we select here is to select a
+	 * size that is one more than the second largest
+	 * pack-file. This ensures that we will repack
+	 * at least two packs if there are three or more
+	 * packs.
+	 */
+	off_t max_size = 0;
+	off_t second_largest_size = 0;
+	off_t result_size;
+	struct packed_git *p;
+	struct repository *r = the_repository;
+
+	reprepare_packed_git(r);
+	for (p = get_all_packs(r); p; p = p->next) {
+		if (p->pack_size > max_size) {
+			second_largest_size = max_size;
+			max_size = p->pack_size;
+		} else if (p->pack_size > second_largest_size)
+			second_largest_size = p->pack_size;
+	}
+
+	result_size = second_largest_size + 1;
+
+	/* But limit ourselves to a batch size of 2g */
+	if (result_size > TWO_GIGABYTES)
+		result_size = TWO_GIGABYTES;
+
+	return result_size;
+}
+
 static int multi_pack_index_repack(struct maintenance_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -1104,7 +1144,8 @@ static int multi_pack_index_repack(struct maintenance_opts *opts)
 	if (opts->quiet)
 		strvec_push(&child.args, "--no-progress");
 
-	strvec_push(&child.args, "--batch-size=0");
+	strvec_pushf(&child.args, "--batch-size=%"PRIuMAX,
+				  (uintmax_t)get_auto_pack_size());
 
 	close_object_store(the_repository->objects);
 
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index be19ac7623..1c5f44f2b3 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -179,10 +179,42 @@ test_expect_success 'incremental-repack task' '
 	test_line_count = 4 packs-between &&
 
 	# the job deletes the two old packs, and does not write
-	# a new one because only one pack remains.
+	# a new one because the batch size is not high enough to
+	# pack the largest pack-file.
 	git maintenance run --task=incremental-repack &&
 	ls .git/objects/pack/*.pack >packs-after &&
-	test_line_count = 1 packs-after
+	test_line_count = 2 packs-after
+'
+
+test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
+	for i in $(test_seq 1 5)
+	do
+		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
+		return 1
+	done &&
+	git add big &&
+	git commit -m "Add big file (1)" &&
+
+	# ensure any possible loose objects are in a pack-file
+	git maintenance run --task=loose-objects &&
+
+	rm big &&
+	for i in $(test_seq 6 10)
+	do
+		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
+		return 1
+	done &&
+	git add big &&
+	git commit -m "Add big file (2)" &&
+
+	# ensure any possible loose objects are in a pack-file
+	git maintenance run --task=loose-objects &&
+
+	# Now run the incremental-repack task and check the batch-size
+	GIT_TRACE2_EVENT="$(pwd)/run-2g.txt" git maintenance run \
+		--task=incremental-repack 2>/dev/null &&
+	test_subcommand git multi-pack-index repack \
+		 --no-progress --batch-size=2147483647 <run-2g.txt
 '
 
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH 9/9] maintenance: add incremental-repack auto condition
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                   ` (7 preceding siblings ...)
  2020-08-06 16:30 ` [PATCH 8/9] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
@ 2020-08-06 16:30 ` Derrick Stolee via GitGitGadget
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-06 16:30 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The incremental-repack task updates the multi-pack-index by deleting pack-
files that have been replaced with new packs, then repacking a batch of
small pack-files into a larger pack-file. This incremental repack is faster
than rewriting all object data, but is slower than some other
maintenance activities.

The 'maintenance.incremental-repack.auto' config option specifies how many
pack-files should exist outside of the multi-pack-index before running
the step. These pack-files could be created by 'git fetch' commands or
by the loose-objects task. The default value is 10.

Setting the option to zero disables the task with the '--auto' option,
and a negative value makes the task run every time.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/maintenance.txt |  9 ++++++++
 builtin/gc.c                         | 31 +++++++++++++++++++++++++++
 t/t7900-maintenance.sh               | 32 ++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+)

diff --git a/Documentation/config/maintenance.txt b/Documentation/config/maintenance.txt
index a9442dd260..22229e7174 100644
--- a/Documentation/config/maintenance.txt
+++ b/Documentation/config/maintenance.txt
@@ -21,3 +21,12 @@ maintenance.loose-objects.auto::
 	positive value implies the command should run when the number of
 	loose objects is at least the value of `maintenance.loose-objects.auto`.
 	The default value is 100.
+
+maintenance.incremental-repack.auto::
+	This integer config option controls how often the `incremental-repack`
+	task should be run as part of `git maintenance run --auto`. If zero,
+	then the `incremental-repack` task will not run with the `--auto`
+	option. A negative value will force the task to run every time.
+	Otherwise, a positive value implies the command should run when the
+	number of pack-files not in the multi-pack-index is at least the value
+	of `maintenance.incremental-repack.auto`. The default value is 10.
diff --git a/builtin/gc.c b/builtin/gc.c
index c09bc1381c..dbf8080d3b 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -31,6 +31,7 @@
 #include "refs.h"
 #include "remote.h"
 #include "midx.h"
+#include "object-store.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -1030,6 +1031,35 @@ static int maintenance_task_loose_objects(struct maintenance_opts *opts)
 	return prune_packed(opts) || pack_loose(opts);
 }
 
+static int incremental_repack_auto_condition(void)
+{
+	struct packed_git *p;
+	int enabled;
+	int incremental_repack_auto_limit = 10;
+	int count = 0;
+
+	if (git_config_get_bool("core.multiPackIndex", &enabled) ||
+	    !enabled)
+		return 0;
+
+	git_config_get_int("maintenance.incremental-repack.auto",
+			   &incremental_repack_auto_limit);
+
+	if (!incremental_repack_auto_limit)
+		return 0;
+	if (incremental_repack_auto_limit < 0)
+		return 1;
+
+	for (p = get_packed_git(the_repository);
+	     count < incremental_repack_auto_limit && p;
+	     p = p->next) {
+		if (!p->multi_pack_index)
+			count++;
+	}
+
+	return count >= incremental_repack_auto_limit;
+}
+
 static int multi_pack_index_write(struct maintenance_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -1220,6 +1250,7 @@ static struct maintenance_task tasks[] = {
 	[TASK_INCREMENTAL_REPACK] = {
 		"incremental-repack",
 		maintenance_task_incremental_repack,
+		incremental_repack_auto_condition,
 	},
 	[TASK_GC] = {
 		"gc",
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 1c5f44f2b3..e1e802e543 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -187,6 +187,7 @@ test_expect_success 'incremental-repack task' '
 '
 
 test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
+
 	for i in $(test_seq 1 5)
 	do
 		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
@@ -217,4 +218,35 @@ test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
 		 --no-progress --batch-size=2147483647 <run-2g.txt
 '
 
+test_expect_success 'maintenance.incremental-repack.auto' '
+	git repack -adk &&
+	git config core.multiPackIndex true &&
+	git multi-pack-index write &&
+	GIT_TRACE2_EVENT="$(pwd)/midx-init.txt" git \
+		-c maintenance.incremental-repack.auto=1 \
+		maintenance run --auto --task=incremental-repack 2>/dev/null &&
+	test_subcommand ! git multi-pack-index write --no-progress <midx-init.txt &&
+	for i in 1 2
+	do
+		test_commit A-$i &&
+		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
+		HEAD
+		^HEAD~1
+		EOF
+		GIT_TRACE2_EVENT=$(pwd)/trace-A-$i git \
+			-c maintenance.incremental-repack.auto=2 \
+			maintenance run --auto --task=incremental-repack 2>/dev/null &&
+		test_subcommand ! git multi-pack-index write --no-progress <trace-A-$i &&
+		test_commit B-$i &&
+		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
+		HEAD
+		^HEAD~1
+		EOF
+		GIT_TRACE2_EVENT=$(pwd)/trace-B-$i git \
+			-c maintenance.incremental-repack.auto=2 \
+			maintenance run --auto --task=incremental-repack 2>/dev/null &&
+		test_subcommand git multi-pack-index write --no-progress <trace-B-$i || return 1
+	done
+'
+
 test_done
-- 
gitgitgadget

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH 8/9] maintenance: auto-size incremental-repack batch
  2020-08-06 16:30 ` [PATCH 8/9] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
@ 2020-08-06 17:02   ` Son Luong Ngoc
  2020-08-06 18:13     ` Derrick Stolee
  0 siblings, 1 reply; 66+ messages in thread
From: Son Luong Ngoc @ 2020-08-06 17:02 UTC (permalink / raw)
  To: Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, Jeff King, congdanhqx,
	phillip.wood123, Emily Shaffer, Jonathan Tan, Derrick Stolee,
	Derrick Stolee

Hi Derrick,

> On Aug 6, 2020, at 18:30, Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com> wrote:
> 
> From: Derrick Stolee <dstolee@microsoft.com>
> 
> When repacking during the 'incremental-repack' task, we use the
> --batch-size option in 'git multi-pack-index repack'. The initial setting
> used --batch-size=0 to repack everything into a single pack-file. This is
> not sustainable for a large repository. The amount of work required is
> also likely to use too many system resources for a background job.
> 
> Update the 'incremental-repack' task by dynamically computing a
> --batch-size option based on the current pack-file structure.
> 
> The dynamic default size is computed with this idea in mind for a client
> repository that was cloned from a very large remote: there is likely one
> "big" pack-file that was created at clone time. Thus, do not try
> repacking it as it is likely packed efficiently by the server.
> 
> Instead, we select the second-largest pack-file, and create a batch size
> that is one larger than that pack-file. If there are three or more
> pack-files, then this guarantees that at least two will be combined into
> a new pack-file.

I have been using this strategy with git-care.sh [1] with large success.
However it worth to note that there are still edge case where I observed that
pack count keep increasing because using '--batch-size=<second-biggest-pack>+1'
did not resulted in any repacking.
In one case, I have observed a local copy went up to 160+ packs without being able
to repack.

I have been considering whether a strategy such as falling back to the '(3rd biggest
pack size) + 1' and 4th and 5th and so on... when midx repack call resulted in no-op,
as that was how I fixed my repo when the edge case happen.

Such strategy would require a way to detect midx repack to signal when no-op happen,
so something like 'git multi-pack-index repack --batch-size=123456 --exit-code' would
be much desirable.

> 
> Of course, this means that the second-largest pack-file size is likely
> to grow over time and may eventually surpass the initially-cloned
> pack-file. Recall that the pack-file batch is selected in a greedy
> manner: the packs are considered from oldest to newest and are selected
> if they have size smaller than the batch size until the total selected
> size is larger than the batch size. Thus, that oldest "clone" pack will
> be first to repack after the new data creates a pack larger than that.
> 
> We also want to place some limits on how large these pack-files become,
> in order to bound the amount of time spent repacking. A maximum
> batch-size of two gigabytes means that large repositories will never be
> packed into a single pack-file using this job, but also that repack is
> rather expensive. This is a trade-off that is valuable to have if the
> maintenance is being run automatically or in the background. Users who
> truly want to optimize for space and performance (and are willing to pay
> the upfront cost of a full repack) can use the 'gc' task to do so.
> 
> Create a test for this two gigabyte limit by creating an EXPENSIVE test
> that generates two pack-files of roughly 2.5 gigabytes in size, then
> performs an incremental repack. Check that the --batch-size argument in
> the subcommand uses the hard-coded maximum.
> 
> Helped-by: Chris Torek <chris.torek@gmail.com>
> Reported-by: Son Luong Ngoc <sluongng@gmail.com>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

Generally, I have found working with '--batch-size' to be a bit unpredictable.
I wonder if we could tweak the behavior somewhat so that its more consistent
to use and test?

Thanks a lot for making this happen.
Hope this patch would make it in stable soon

Cheers,
Son Luong.

[1]: https://github.com/sluongng/git-care

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH 8/9] maintenance: auto-size incremental-repack batch
  2020-08-06 17:02   ` Son Luong Ngoc
@ 2020-08-06 18:13     ` Derrick Stolee
  0 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee @ 2020-08-06 18:13 UTC (permalink / raw)
  To: Son Luong Ngoc, Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, Jeff King, congdanhqx,
	phillip.wood123, Emily Shaffer, Jonathan Tan, Derrick Stolee,
	Derrick Stolee

On 8/6/2020 1:02 PM, Son Luong Ngoc wrote:
> Hi Derrick,
> 
>> On Aug 6, 2020, at 18:30, Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com> wrote:
>>
>> From: Derrick Stolee <dstolee@microsoft.com>
>>
>> When repacking during the 'incremental-repack' task, we use the
>> --batch-size option in 'git multi-pack-index repack'. The initial setting
>> used --batch-size=0 to repack everything into a single pack-file. This is
>> not sustainable for a large repository. The amount of work required is
>> also likely to use too many system resources for a background job.
>>
>> Update the 'incremental-repack' task by dynamically computing a
>> --batch-size option based on the current pack-file structure.
>>
>> The dynamic default size is computed with this idea in mind for a client
>> repository that was cloned from a very large remote: there is likely one
>> "big" pack-file that was created at clone time. Thus, do not try
>> repacking it as it is likely packed efficiently by the server.
>>
>> Instead, we select the second-largest pack-file, and create a batch size
>> that is one larger than that pack-file. If there are three or more
>> pack-files, then this guarantees that at least two will be combined into
>> a new pack-file.
> 
> I have been using this strategy with git-care.sh [1] with large success.
> However it worth to note that there are still edge case where I observed that
> pack count keep increasing because using '--batch-size=<second-biggest-pack>+1'
> did not resulted in any repacking.
> In one case, I have observed a local copy went up to 160+ packs without being able
> to repack.
> 
> I have been considering whether a strategy such as falling back to the '(3rd biggest
> pack size) + 1' and 4th and 5th and so on... when midx repack call resulted in no-op,
> as that was how I fixed my repo when the edge case happen.
> 
> Such strategy would require a way to detect midx repack to signal when no-op happen,
> so something like 'git multi-pack-index repack --batch-size=123456 --exit-code' would
> be much desirable.
> 
>>
>> Of course, this means that the second-largest pack-file size is likely
>> to grow over time and may eventually surpass the initially-cloned
>> pack-file. Recall that the pack-file batch is selected in a greedy
>> manner: the packs are considered from oldest to newest and are selected
>> if they have size smaller than the batch size until the total selected
>> size is larger than the batch size. Thus, that oldest "clone" pack will
>> be first to repack after the new data creates a pack larger than that.
>>
>> We also want to place some limits on how large these pack-files become,
>> in order to bound the amount of time spent repacking. A maximum
>> batch-size of two gigabytes means that large repositories will never be
>> packed into a single pack-file using this job, but also that repack is
>> rather expensive. This is a trade-off that is valuable to have if the
>> maintenance is being run automatically or in the background. Users who
>> truly want to optimize for space and performance (and are willing to pay
>> the upfront cost of a full repack) can use the 'gc' task to do so.
>>
>> Create a test for this two gigabyte limit by creating an EXPENSIVE test
>> that generates two pack-files of roughly 2.5 gigabytes in size, then
>> performs an incremental repack. Check that the --batch-size argument in
>> the subcommand uses the hard-coded maximum.
>>
>> Helped-by: Chris Torek <chris.torek@gmail.com>
>> Reported-by: Son Luong Ngoc <sluongng@gmail.com>
>> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> 
> Generally, I have found working with '--batch-size' to be a bit unpredictable.
> I wonder if we could tweak the behavior somewhat so that its more consistent
> to use and test?

Thanks for continuing to test with this model. My experience has been limited
to the --batch-size=2g option on repos that typically have >15gb of commit
and tree data in their pack directory.

One bit of unpredictability that we've seen is that the --batch-size uses
the "expected size" of a pack-file to select if it should be repacked. This
only tracks the objects that are referenced in that pack, so when we have
new packs that were "un-thinned" by duplicating delta-bases, those affect
the expected size of a repack.

Here is a great reason to have this series be split. While part I stabilizes,
we can take the time to re-evaluate this strategy. It might require updating
the multi-pack-index builtin itself.

One thing to think about is to focus on the different possible sizes of a
repository. If the entire pack-directory is small, then we might as well
repack everything. (What should the limit be? 2gb? configurable?) In the
case of a larger directory, should we just use the --batch-size logic with
that limit, or should we create a new option for which packs to repack?

For example, the recent simulation [1] of downloading fetch packs and
running this maintenance did see extra space that could be recovered with
the current logic. However, what if we could specify "repack everything
except the largest pack" exactly? That would do exactly what this task
is _intending_, as long as that resulting pack-file does not exceed the
2gb maximum by too much.

[1] https://lore.kernel.org/git/d50fbb33-9be3-1c48-2277-8bf894df734f@gmail.com/

I will think more on this. I'm open to alternate strategies.

Thanks,
-Stolee

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update
  2020-08-06 16:30 ` [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
@ 2020-08-12 23:10   ` Emily Shaffer
  2020-08-13  0:03     ` Junio C Hamano
  0 siblings, 1 reply; 66+ messages in thread
From: Emily Shaffer @ 2020-08-12 23:10 UTC (permalink / raw)
  To: Junio C Hamano via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, sluongng, jonathantanmy, Derrick Stolee,
	Junio C Hamano

[Note: like last time, this was the subject of our team's review club
this week, so I'll try to cite individual comments. -Emily]

On Thu, Aug 06, 2020 at 04:30:16PM +0000, Junio C Hamano via GitGitGadget wrote:
> 
> +fetch.writeFetchHEAD::
> +	Setting it to false tells `git fetch` not to write the list
> +	of remote refs fetched in the `FETCH_HEAD` file directly
> +	under `$GIT_DIR`.  Can be countermanded from the command
> +	line with the `--[no-]write-fetch-head` option.  Defaults to
> +	true.

[jrnieder] Is providing a config option creating more trouble than
benefit? Is this a burden on script authors that they need to check the
config state, when instead they could just pass the flag? Or rather,
because of the config, the script author has to pass the flag explicitly
anyways.
[emily] removing the config also clears up the confusion around 'git pull' +
'fetch.writeFetchHEAD' I commented on later.

> @@ -895,7 +902,9 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
>  	const char *what, *kind;
>  	struct ref *rm;
>  	char *url;
> -	const char *filename = dry_run ? "/dev/null" : git_path_fetch_head(the_repository);
> +	const char *filename = (!write_fetch_head
> +				? "/dev/null"
> +				: git_path_fetch_head(the_repository));

[emily] Huh. so what does the dry_run codepath look like now? It looks
like it's been superseded by write_fetch_head but the option parse
doesn't tell dry_run to update write_fetch_head instead. (Found the
answer later, see below)

> @@ -1797,6 +1806,10 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
>  	if (depth || deepen_since || deepen_not.nr)
>  		deepen = 1;
>  
> +	/* FETCH_HEAD never gets updated in --dry-run mode */
> +	if (dry_run)
> +		write_fetch_head = 0;

[emily] Aha, here is where dry_run informs write_fetch_head. I wonder if
there's a way to instead tell the options struct that --dry-run ~=
--write-fetch-head?

> +test_expect_success '--write-fetch-head gets defeated by --dry-run' '
> +	rm -f .git/FETCH_HEAD &&
> +	git fetch --dry-run --write-fetch-head . &&
> +	! test -f .git/FETCH_HEAD
> +'

[emily] Would it make more sense to make these args mutually exclusive?
[jrnieder] If someone specifies both, then they probably want to say
"show me what I would write to FETCH_HEAD but don't actually do that" -
which isn't info that we print anyways, right now.

> +
> +test_expect_success 'fetch.writeFetchHEAD and FETCH_HEAD' '
> +	rm -f .git/FETCH_HEAD &&
> +	git -c fetch.writeFetchHEAD=no fetch . &&
> +	! test -f .git/FETCH_HEAD
> +'
> +
> +test_expect_success 'fetch.writeFetchHEAD gets defeated by --dry-run' '
> +	rm -f .git/FETCH_HEAD &&
> +	git -c fetch.writeFetchHEAD=yes fetch --dry-run . &&
> +	! test -f .git/FETCH_HEAD
> +'
> +
> +test_expect_success 'fetch.writeFetchHEAD and --no-write-fetch-head' '
> +	rm -f .git/FETCH_HEAD &&
> +	git -c fetch.writeFetchHEAD=yes fetch --no-write-fetch-head . &&
> +	! test -f .git/FETCH_HEAD
> +'
> +
> +test_expect_success 'fetch.writeFetchHEAD and --write-fetch-head' '
> +	rm -f .git/FETCH_HEAD &&
> +	git -c fetch.writeFetchHEAD=no fetch --write-fetch-head . &&
> +	test -f .git/FETCH_HEAD
> +'
[jrnieder] Thanks for being thorough about these.

> +test_expect_success 'git pull --no-write-fetch-head fails' '
> +	mkdir clonedwfh &&
> +	(cd clonedwfh && git init &&
> +	test_must_fail git pull --no-write-fetch-head "../parent" >out 2>err &&
> +	test_must_be_empty out &&
> +	test_i18ngrep "no-write-fetch-head" err)

Should this be shown as a usage error instead of a die()?

> +'
> +
> +test_expect_success 'git pull succeeds with fetch.writeFetchHEAD=false' '
> +	mkdir clonedwfhconfig &&
> +	(cd clonedwfhconfig && git init &&
> +	git config fetch.writeFetchHEAD false &&
> +	git pull "../parent" >out 2>err &&
> +	grep FETCH_HEAD err)

[emily] I guess it's a little surprising that my config is being overridden
without any warning... although pull can't possibly work if FETCH_HEAD
isn't updated. I am conflicted about this use case..
[jrnieder] This is another argument to drop the config from this patch,
unless we are thinking of changing the default behavior of
--[no-]write-fetch-head.


^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH 2/9] maintenance: add prefetch task
  2020-08-06 16:30 ` [PATCH 2/9] maintenance: add prefetch task Derrick Stolee via GitGitGadget
@ 2020-08-12 23:10   ` Emily Shaffer
  2020-08-14  1:28     ` Derrick Stolee
  0 siblings, 1 reply; 66+ messages in thread
From: Emily Shaffer @ 2020-08-12 23:10 UTC (permalink / raw)
  To: Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

On Thu, Aug 06, 2020 at 04:30:17PM +0000, Derrick Stolee via GitGitGadget wrote:
> 
> 3. By adding a new refspec "+refs/heads/*:refs/prefetch/<remote>/*"
>    we can ensure that we actually load the new values somewhere in
>    our refspace while not updating refs/heads or refs/remotes. By
>    storing these refs here, the commit-graph job will update the
>    commit-graph with the commits from these hidden refs.

[emily] How does the content of refs/prefetch/* get used?
[jrnieder] How does the content of refs/prefetch/* get cleaned up?
[jonathantan] refs/prefetch/* will get used in negotiation so it is
useful to keep these.
> 
> 4. --prune will delete the refs/prefetch/<remote> refs that no
>    longer appear on the remote.
[jrnieder] this is what cleans up refs/prefetch/* later :)

> +static int fetch_remote(const char *remote, struct maintenance_opts *opts)
> +{
> +	struct child_process child = CHILD_PROCESS_INIT;
> +
> +	child.git_cmd = 1;
> +	strvec_pushl(&child.args, "fetch", remote, "--prune", "--no-tags",
> +		     "--no-write-fetch-head", "--refmap=", NULL);
[jonathantan] It would be good to pass --recurse-submodules=no.
[jrnieder] Since we are specifying the refmap here, if we were to
recurse into submodules, we'd have to be careful about making sure
refmap gets propagated correctly.

> +static int fill_each_remote(struct remote *remote, void *cbdata)
[jrnieder] Since this is a callback that happens for each remote, maybe
this should be named to indicate it only fills one remote at a time
instead. Nit :)
> +{
> +	struct string_list *remotes = (struct string_list *)cbdata;
> +
> +	string_list_append(remotes, remote->name);
> +	return 0;
> +}
> +
> +static int maintenance_task_prefetch(struct maintenance_opts *opts)
> +{
> +	int result = 0;
> +	struct string_list_item *item;
> +	struct string_list remotes = STRING_LIST_INIT_DUP;
> +
> +	if (for_each_remote(fill_each_remote, &remotes)) {
> +		error(_("failed to fill remotes"));
> +		result = 1;
> +		goto cleanup;
> +	}
> +
> +	for (item = remotes.items;
> +	     item && item < remotes.items + remotes.nr;
> +	     item++)

Is there a reason not to use for_each_string_list_item() instead? This
would be more brief and also easier to read (less thinking about what
the loop is doing).

> +		result |= fetch_remote(item->string, opts);
> +
> +cleanup:
> +	string_list_clear(&remotes, 0);
> +	return result;
> +}
> +

>  enum maintenance_task_label {
> +	TASK_PREFETCH,
[jrnieder] Nit: Is there a sort order for these? Should we establish an order
early on (e.g. alphabetical)?
>  	TASK_GC,
>  	TASK_COMMIT_GRAPH,

> +test_expect_success 'prefetch multiple remotes' '
> +	git clone . clone1 &&
> +	git clone . clone2 &&
> +	git remote add remote1 "file://$(pwd)/clone1" &&
> +	git remote add remote2 "file://$(pwd)/clone2" &&
> +	git -C clone1 switch -c one &&
> +	git -C clone2 switch -c two &&
> +	test_commit -C clone1 one &&
> +	test_commit -C clone2 two &&
> +	GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null &&
> +	fetchargs="--prune --no-tags --no-write-fetch-head --refmap= --quiet" &&
> +	test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\* <run-prefetch.txt &&
[jrnieder] In practice, why were all the \\ needed? Trying to figure out
where Git is using a shell that would need the * escaped and finding it
hard to reason about.
> +	test_subcommand git fetch remote2 $fetchargs +refs/heads/\\*:refs/prefetch/remote2/\\* <run-prefetch.txt &&
> +	test_path_is_missing .git/refs/remotes &&
> +	test_cmp clone1/.git/refs/heads/one .git/refs/prefetch/remote1/one &&
> +	test_cmp clone2/.git/refs/heads/two .git/refs/prefetch/remote2/two &&
[jrnieder] Should we use test_cmp_rev instead to make compatible with
packed-refs?
> +	git log prefetch/remote1/one &&
> +	git log prefetch/remote2/two
[jonathantan] Why do we use 'git log' to check? I'm a little confused
about what's going on; if you just want to check that the refs are
present you could use 'git rev-parse' instead?

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH 3/9] maintenance: add loose-objects task
  2020-08-06 16:30 ` [PATCH 3/9] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
@ 2020-08-12 23:10   ` Emily Shaffer
  2020-08-14  1:46     ` Derrick Stolee
  0 siblings, 1 reply; 66+ messages in thread
From: Emily Shaffer @ 2020-08-12 23:10 UTC (permalink / raw)
  To: Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

On Thu, Aug 06, 2020 at 04:30:18PM +0000, Derrick Stolee via GitGitGadget wrote:

> diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
> index bb0d5eded4..898aff4726 100644
> --- a/Documentation/git-maintenance.txt
> +++ b/Documentation/git-maintenance.txt
> @@ -80,6 +80,17 @@ gc::
>  	It can also be disruptive in some situations, as it deletes stale
>  	data.
>  
> +loose-objects::
> +	The `loose-objects` job cleans up loose objects and places them into
> +	pack-files. In order to prevent race conditions with concurrent Git
> +	commands, it follows a two-step process. First, it deletes any loose
> +	objects that already exist in a pack-file; concurrent Git processes
> +	will examine the pack-file for the object data instead of the loose
> +	object. Second, it creates a new pack-file (starting with "loose-")
> +	containing a batch of loose objects. The batch size is limited to 50
> +	thousand objects to prevent the job from taking too long on a
> +	repository with many loose objects.

[emily] What's not said is what happens to loose-* packfile. Does this
get repacked and disappear, is it treated differently, etc?
[jonathantan] This is treated the same as any other pack. Is there a
reason to call it loose-*?
[jrnieder] It seems like unreachable objects will get stuck going in and
out of this pack, right? unreachable loose obj -> loose-*.pack ->
repack, unreachable becomes loose -> repeat

> +static int prune_packed(struct maintenance_opts *opts)
> +{
> +	struct child_process child = CHILD_PROCESS_INIT;
> +
> +	child.git_cmd = 1;
> +	strvec_push(&child.args, "prune-packed");
> +
> +	if (opts->quiet)
> +		strvec_push(&child.args, "--quiet");
> +
> +	return !!run_command(&child);
[emily] Why not report the error code here to the caller? Is there a
path to notify user of errors that require user intervention?
[jrnieder] Some errors might be expected and some might not, so should
we handle them differently?
[emily] Probably makes more sense to revisit this in the far future when
we teach 'git maintenance' to send us emails and flashing lights when
our jobs fail, instead of worrying about it now :)
[jrnieder] Imagine if we got exit 127 because the usage we are using is
wrong - in that case, for example, we would want to BUG()

> +static int write_loose_object_to_stdin(const struct object_id *oid,
> +				       const char *path,
> +				       void *data)
> +{
> +	struct write_loose_object_data *d = (struct write_loose_object_data *)data;
[jrnieder] Since we are enlightened C developers, not C++ developers,
you can skip the explicit cast.

> +++ b/t/t7900-maintenance.sh
> @@ -83,4 +83,43 @@ test_expect_success 'prefetch multiple remotes' '
>  	git log prefetch/remote2/two
>  '
>  
> +test_expect_success 'loose-objects task' '
[jrnieder] Unrelated to this change, this test makes me sad that we
don't have better low-level test helpers to enable this kind of testing.
Makes me wish for something better :)
> +	# Repack everything so we know the state of the object dir
> +	git repack -adk &&
> +
> +	# Hack to stop maintenance from running during "git commit"
> +	echo in use >.git/objects/maintenance.lock &&
> +
> +	# Assuming that "git commit" creates at least one loose object
> +	test_commit create-loose-object &&
> +	rm .git/objects/maintenance.lock &&
> +
> +	ls .git/objects >obj-dir-before &&
> +	test_file_not_empty obj-dir-before &&
> +	ls .git/objects/pack/*.pack >packs-before &&
> +	test_line_count = 1 packs-before &&
> +
> +	# The first run creates a pack-file
> +	# but does not delete loose objects.
> +	git maintenance run --task=loose-objects &&
> +	ls .git/objects >obj-dir-between &&
> +	test_cmp obj-dir-before obj-dir-between &&
> +	ls .git/objects/pack/*.pack >packs-between &&
> +	test_line_count = 2 packs-between &&
> +	ls .git/objects/pack/loose-*.pack >loose-packs &&
> +	test_line_count = 1 loose-packs &&
> +
> +	# The second run deletes loose objects
> +	# but does not create a pack-file.
> +	git maintenance run --task=loose-objects &&
> +	ls .git/objects >obj-dir-after &&
> +	cat >expect <<-\EOF &&
> +	info
> +	pack
> +	EOF
> +	test_cmp expect obj-dir-after &&
> +	ls .git/objects/pack/*.pack >packs-after &&
> +	test_cmp packs-between packs-after
> +'
> +


^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update
  2020-08-12 23:10   ` Emily Shaffer
@ 2020-08-13  0:03     ` Junio C Hamano
  2020-08-13  1:45       ` Jonathan Nieder
  2020-08-13  4:37       ` [PATCH v3] " Junio C Hamano
  0 siblings, 2 replies; 66+ messages in thread
From: Junio C Hamano @ 2020-08-13  0:03 UTC (permalink / raw)
  To: Emily Shaffer
  Cc: Junio C Hamano via GitGitGadget, git, sandals, steadmon,
	jrnieder, peff, congdanhqx, phillip.wood123, sluongng,
	jonathantanmy, Derrick Stolee

Emily Shaffer <emilyshaffer@google.com> writes:

>> +fetch.writeFetchHEAD::
>> +	Setting it to false tells `git fetch` not to write the list
>> +	of remote refs fetched in the `FETCH_HEAD` file directly
>> +	under `$GIT_DIR`.  Can be countermanded from the command
>> +	line with the `--[no-]write-fetch-head` option.  Defaults to
>> +	true.
>
> [jrnieder] Is providing a config option creating more trouble than
> benefit? Is this a burden on script authors that they need to check the
> config state, when instead they could just pass the flag? Or rather,
> because of the config, the script author has to pass the flag explicitly
> anyways.
> [emily] removing the config also clears up the confusion around 'git pull' +
> 'fetch.writeFetchHEAD' I commented on later.

[A meta comment, but I somehow find this format cumbersome to read
and respond to.  Would it be possible to dedup and/or summarize
comments on a single point?]

I do not think "it becomes cumbersome to design interaction between
command line option and configuration" is a valid reason not to add
configuration variable.  It would be a valid reason not to, if we
have a convincing argument why people won't pass the command line
option very often, though, but you'd need to be prepared for a
possible future in which somebody finds a good use case where a
configuration is useful, which means you cannot forever depend on
the lack of configurability to avoid making a proper design of the
interaction between configuration and command line.

As the feature itself is primarily designed for scripts that want to
always disable writing of FETCH_HEAD, I can certainly understand a
short-term/sighted view of not wanting to add configuration, though.

>> @@ -895,7 +902,9 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
>>  	const char *what, *kind;
>>  	struct ref *rm;
>>  	char *url;
>> -	const char *filename = dry_run ? "/dev/null" : git_path_fetch_head(the_repository);
>> +	const char *filename = (!write_fetch_head
>> +				? "/dev/null"
>> +				: git_path_fetch_head(the_repository));
>
> [emily] Huh. so what does the dry_run codepath look like now? It looks
> like it's been superseded by write_fetch_head but the option parse
> doesn't tell dry_run to update write_fetch_head instead. (Found the
> answer later, see below)
>
>> @@ -1797,6 +1806,10 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
>>  	if (depth || deepen_since || deepen_not.nr)
>>  		deepen = 1;
>>  
>> +	/* FETCH_HEAD never gets updated in --dry-run mode */
>> +	if (dry_run)
>> +		write_fetch_head = 0;
>
> [emily] Aha, here is where dry_run informs write_fetch_head. I wonder if
> there's a way to instead tell the options struct that --dry-run ~=
> --write-fetch-head?

I do not know with what meaning you used the symbol "~=".  Dry-run
tells the command to operate differently in a few ways, and one of
the (smaller) ways is not to write the FETCH_HEAD file.  Did you
mean "contains", "includes", etc.?

>> +test_expect_success '--write-fetch-head gets defeated by --dry-run' '
>> +	rm -f .git/FETCH_HEAD &&
>> +	git fetch --dry-run --write-fetch-head . &&
>> +	! test -f .git/FETCH_HEAD
>> +'
>
> [emily] Would it make more sense to make these args mutually exclusive?

At least, give a hint, if you cannot state in concrete words, why
you suspect it might make sense to do things differently.  What use
case do you think an alternative design would help better?  Without
it, you can just get "no" and such an exchange would not be useful
at all to improve the patch.

> [jrnieder] If someone specifies both, then they probably want to say
> "show me what I would write to FETCH_HEAD but don't actually do that" -
> which isn't info that we print anyways, right now.

Do you mean "don't actually write but show it to standard output
instead" or something?  If we were designing --dry-run from scratch
back when there were no "git fetch" command, that would have made
tons of sense, I think ;-) To me, the "--write-fetch-head" option
tells it to "write to the file", and not "write the info to unfixed
destination that is not specified by this option but derived by the
presense of other options".  While the "don't download and show what
would be in FETCH_HEAD" might be a good feature to add, combining
these two options may be a good way to invoke the feature.

>> +test_expect_success 'git pull --no-write-fetch-head fails' '
>> +	mkdir clonedwfh &&
>> +	(cd clonedwfh && git init &&
>> +	test_must_fail git pull --no-write-fetch-head "../parent" >out 2>err &&
>> +	test_must_be_empty out &&
>> +	test_i18ngrep "no-write-fetch-head" err)
>
> Should this be shown as a usage error instead of a die()?

As "pull" does and should not take "--[no-]write-fetch-head" as its
option, I think the above command line deserves an usage error, just
like "git pull --update-head-ok" does (or "git pull --no-such-option"
for that matter).


^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update
  2020-08-13  0:03     ` Junio C Hamano
@ 2020-08-13  1:45       ` Jonathan Nieder
  2020-08-13  4:37       ` [PATCH v3] " Junio C Hamano
  1 sibling, 0 replies; 66+ messages in thread
From: Jonathan Nieder @ 2020-08-13  1:45 UTC (permalink / raw)
  To: Junio C Hamano
  Cc: Emily Shaffer, Junio C Hamano via GitGitGadget, git, sandals,
	steadmon, peff, congdanhqx, phillip.wood123, sluongng,
	jonathantanmy, Derrick Stolee

Junio C Hamano wrote:

> As the feature itself is primarily designed for scripts that want to
> always disable writing of FETCH_HEAD, I can certainly understand a
> short-term/sighted view of not wanting to add configuration, though.

Yes, I think that since this feature is primarily designed for
scripts, an option is more likely to be useful for them than a config
setting.  An option kicks in when the calling script requests it; a
config setting can kick in even when they didn't intend to request it.

My opinion would change if we think that we're going to flip the
default to --no-write-fetch-head some day, in which case a config
setting would be a good way to request a preview of the future.  But I
don't believe anyone's brought that up as a direction we want to
pursue.

[...]
>>            If someone specifies both, then they probably want to say
>> "show me what I would write to FETCH_HEAD but don't actually do that" -
>> which isn't info that we print anyways, right now.
>
> Do you mean "don't actually write but show it to standard output
> instead" or something?

My take is that the behavior that the patch implements for --dry-run
--write-fetch-head is correct and what a user would want: it acts *as
though* you passed --write-fetch-head (including producing the same
console output), without producing mutations that the user might
regret (such as updating FETCH_HEAD).

Thanks and hope that helps,
Jonathan

^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3] fetch: optionally allow disabling FETCH_HEAD update
  2020-08-13  0:03     ` Junio C Hamano
  2020-08-13  1:45       ` Jonathan Nieder
@ 2020-08-13  4:37       ` Junio C Hamano
  2020-08-14  1:13         ` Derrick Stolee
  1 sibling, 1 reply; 66+ messages in thread
From: Junio C Hamano @ 2020-08-13  4:37 UTC (permalink / raw)
  To: Jonathan Nieder
  Cc: Junio C Hamano via GitGitGadget, git, Derrick Stolee, Emily Shaffer

If you run fetch but record the result in remote-tracking branches,
and either if you do nothing with the fetched refs (e.g. you are
merely mirroring) or if you always work from the remote-tracking
refs (e.g. you fetch and then merge origin/branchname separately),
you can get away with having no FETCH_HEAD at all.

Teach "git fetch" a command line option "--[no-]write-fetch-head".
The default is to write FETCH_HEAD, and the option is primarily
meant to be used with the "--no-" prefix to override this default,
because there is no matching fetch.writeFetchHEAD configuration
variable to flip the default to off (in which case, the positive
form may become necessary to defeat it).

Note that under "--dry-run" mode, FETCH_HEAD is never written;
otherwise you'd see list of objects in the file that you do not
actually have.  Passing `--write-fetch-head` does not force `git
fetch` to write the file.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * So, it becomes much smaller by punting the whole configuration
   thing, as we do not need the extra code for config parsing and
   there is no need for code to override the user configuration when
   driving "git fetch" from "git pull".

 Documentation/fetch-options.txt |  9 +++++++++
 builtin/fetch.c                 | 15 ++++++++++++---
 t/t5510-fetch.sh                | 15 +++++++++++++--
 3 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index 495bc8ab5a..b65a758661 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -64,6 +64,15 @@ documented in linkgit:git-config[1].
 --dry-run::
 	Show what would be done, without making any changes.
 
+ifndef::git-pull[]
+--[no-]write-fetch-head::
+	Write the list of remote refs fetched in the `FETCH_HEAD`
+	file directly under `$GIT_DIR`.  This is the default.
+	Passing `--no-write-fetch-head` from the command line tells
+	Git not to write the file.  Under `--dry-run` option, the
+	file is never written.
+endif::git-pull[]
+
 -f::
 --force::
 	When 'git fetch' is used with `<src>:<dst>` refspec it may
diff --git a/builtin/fetch.c b/builtin/fetch.c
index c8b9366d3c..cb38e6f5ec 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -56,6 +56,7 @@ static int prune_tags = -1; /* unspecified */
 #define PRUNE_TAGS_BY_DEFAULT 0 /* do we prune tags by default? */
 
 static int all, append, dry_run, force, keep, multiple, update_head_ok;
+static int write_fetch_head = 1;
 static int verbosity, deepen_relative, set_upstream;
 static int progress = -1;
 static int enable_auto_gc = 1;
@@ -162,6 +163,8 @@ static struct option builtin_fetch_options[] = {
 		    PARSE_OPT_OPTARG, option_fetch_parse_recurse_submodules),
 	OPT_BOOL(0, "dry-run", &dry_run,
 		 N_("dry run")),
+	OPT_BOOL(0, "write-fetch-head", &write_fetch_head,
+		 N_("write fetched references to the FETCH_HEAD file")),
 	OPT_BOOL('k', "keep", &keep, N_("keep downloaded pack")),
 	OPT_BOOL('u', "update-head-ok", &update_head_ok,
 		    N_("allow updating of HEAD ref")),
@@ -895,7 +898,9 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 	const char *what, *kind;
 	struct ref *rm;
 	char *url;
-	const char *filename = dry_run ? "/dev/null" : git_path_fetch_head(the_repository);
+	const char *filename = (!write_fetch_head
+				? "/dev/null"
+				: git_path_fetch_head(the_repository));
 	int want_status;
 	int summary_width = transport_summary_width(ref_map);
 
@@ -1329,7 +1334,7 @@ static int do_fetch(struct transport *transport,
 	}
 
 	/* if not appending, truncate FETCH_HEAD */
-	if (!append && !dry_run) {
+	if (!append && write_fetch_head) {
 		retcode = truncate_fetch_head();
 		if (retcode)
 			goto cleanup;
@@ -1596,7 +1601,7 @@ static int fetch_multiple(struct string_list *list, int max_children)
 	int i, result = 0;
 	struct strvec argv = STRVEC_INIT;
 
-	if (!append && !dry_run) {
+	if (!append && write_fetch_head) {
 		int errcode = truncate_fetch_head();
 		if (errcode)
 			return errcode;
@@ -1797,6 +1802,10 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	if (depth || deepen_since || deepen_not.nr)
 		deepen = 1;
 
+	/* FETCH_HEAD never gets updated in --dry-run mode */
+	if (dry_run)
+		write_fetch_head = 0;
+
 	if (all) {
 		if (argc == 1)
 			die(_("fetch --all does not take a repository argument"));
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 9850ecde5d..5bd1f953af 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -539,13 +539,24 @@ test_expect_success 'fetch into the current branch with --update-head-ok' '
 
 '
 
-test_expect_success 'fetch --dry-run' '
-
+test_expect_success 'fetch --dry-run does not touch FETCH_HEAD' '
 	rm -f .git/FETCH_HEAD &&
 	git fetch --dry-run . &&
 	! test -f .git/FETCH_HEAD
 '
 
+test_expect_success '--no-write-fetch-head does not touch FETCH_HEAD' '
+	rm -f .git/FETCH_HEAD &&
+	git fetch --no-write-fetch-head . &&
+	! test -f .git/FETCH_HEAD
+'
+
+test_expect_success '--write-fetch-head gets defeated by --dry-run' '
+	rm -f .git/FETCH_HEAD &&
+	git fetch --dry-run --write-fetch-head . &&
+	! test -f .git/FETCH_HEAD
+'
+
 test_expect_success "should be able to fetch with duplicate refspecs" '
 	mkdir dups &&
 	(
-- 
2.28.0-314-g35e3b9c6bd



^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3] fetch: optionally allow disabling FETCH_HEAD update
  2020-08-13  4:37       ` [PATCH v3] " Junio C Hamano
@ 2020-08-14  1:13         ` Derrick Stolee
  2020-08-14  1:32           ` Junio C Hamano
  0 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee @ 2020-08-14  1:13 UTC (permalink / raw)
  To: Junio C Hamano, Jonathan Nieder
  Cc: Junio C Hamano via GitGitGadget, git, Derrick Stolee, Emily Shaffer

On 8/13/2020 12:37 AM, Junio C Hamano wrote:
> If you run fetch but record the result in remote-tracking branches,
> and either if you do nothing with the fetched refs (e.g. you are
> merely mirroring) or if you always work from the remote-tracking
> refs (e.g. you fetch and then merge origin/branchname separately),
> you can get away with having no FETCH_HEAD at all.
> 
> Teach "git fetch" a command line option "--[no-]write-fetch-head".
> The default is to write FETCH_HEAD, and the option is primarily
> meant to be used with the "--no-" prefix to override this default,
> because there is no matching fetch.writeFetchHEAD configuration
> variable to flip the default to off (in which case, the positive
> form may become necessary to defeat it).
> 
> Note that under "--dry-run" mode, FETCH_HEAD is never written;
> otherwise you'd see list of objects in the file that you do not
> actually have.  Passing `--write-fetch-head` does not force `git
> fetch` to write the file.
> 
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
> 
>  * So, it becomes much smaller by punting the whole configuration
>    thing, as we do not need the extra code for config parsing and
>    there is no need for code to override the user configuration when
>    driving "git fetch" from "git pull".

Sounds good. I'll incorporate this patch into my next version,
except it seems you dropped this test:

diff --git a/t/t5521-pull-options.sh b/t/t5521-pull-options.sh
index 159afa7ac8..db1a381cd9 100755
--- a/t/t5521-pull-options.sh
+++ b/t/t5521-pull-options.sh
@@ -85,6 +85,13 @@ test_expect_success 'git pull --cleanup errors early on invalid argument' '
        test -s err)
 '
 
+test_expect_success 'git pull --no-write-fetch-head fails' '
+       mkdir clonedwfh &&
+       (cd clonedwfh && git init &&
+       test_expect_code 129 git pull --no-write-fetch-head "../parent" >out 2>err &&
+       test_must_be_empty out &&
+       test_i18ngrep "no-write-fetch-head" err)
+'
 
 test_expect_success 'git pull --force' '
        mkdir clonedoldstyle &&

which I changed "test_must_fail" to "test_expect_code 129" to
demonstrate that this is a usage error, not just any error.

Thanks,
-Stolee

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH 2/9] maintenance: add prefetch task
  2020-08-12 23:10   ` Emily Shaffer
@ 2020-08-14  1:28     ` Derrick Stolee
  0 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee @ 2020-08-14  1:28 UTC (permalink / raw)
  To: Emily Shaffer, Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

On 8/12/2020 7:10 PM, Emily Shaffer wrote:
> On Thu, Aug 06, 2020 at 04:30:17PM +0000, Derrick Stolee via GitGitGadget wrote:
>>
>> 3. By adding a new refspec "+refs/heads/*:refs/prefetch/<remote>/*"
>>    we can ensure that we actually load the new values somewhere in
>>    our refspace while not updating refs/heads or refs/remotes. By
>>    storing these refs here, the commit-graph job will update the
>>    commit-graph with the commits from these hidden refs.
> 
> [emily] How does the content of refs/prefetch/* get used?
> [jrnieder] How does the content of refs/prefetch/* get cleaned up?
> [jonathantan] refs/prefetch/* will get used in negotiation so it is
> useful to keep these.
>>
>> 4. --prune will delete the refs/prefetch/<remote> refs that no
>>    longer appear on the remote.
> [jrnieder] this is what cleans up refs/prefetch/* later :)
> 
>> +static int fetch_remote(const char *remote, struct maintenance_opts *opts)
>> +{
>> +	struct child_process child = CHILD_PROCESS_INIT;
>> +
>> +	child.git_cmd = 1;
>> +	strvec_pushl(&child.args, "fetch", remote, "--prune", "--no-tags",
>> +		     "--no-write-fetch-head", "--refmap=", NULL);
> [jonathantan] It would be good to pass --recurse-submodules=no.
> [jrnieder] Since we are specifying the refmap here, if we were to
> recurse into submodules, we'd have to be careful about making sure
> refmap gets propagated correctly.

Good point.

>> +static int fill_each_remote(struct remote *remote, void *cbdata)
> [jrnieder] Since this is a callback that happens for each remote, maybe
> this should be named to indicate it only fills one remote at a time
> instead. Nit :)

Sure. append_remote() is better.

>> +{
>> +	struct string_list *remotes = (struct string_list *)cbdata;
>> +
>> +	string_list_append(remotes, remote->name);
>> +	return 0;
>> +}
>> +
>> +static int maintenance_task_prefetch(struct maintenance_opts *opts)
>> +{
>> +	int result = 0;
>> +	struct string_list_item *item;
>> +	struct string_list remotes = STRING_LIST_INIT_DUP;
>> +
>> +	if (for_each_remote(fill_each_remote, &remotes)) {
>> +		error(_("failed to fill remotes"));
>> +		result = 1;
>> +		goto cleanup;
>> +	}
>> +
>> +	for (item = remotes.items;
>> +	     item && item < remotes.items + remotes.nr;
>> +	     item++)
> 
> Is there a reason not to use for_each_string_list_item() instead? This
> would be more brief and also easier to read (less thinking about what
> the loop is doing).

I just keep forgetting about that macro. Thanks.

>> +		result |= fetch_remote(item->string, opts);
>> +
>> +cleanup:
>> +	string_list_clear(&remotes, 0);
>> +	return result;
>> +}
>> +
> 
>>  enum maintenance_task_label {
>> +	TASK_PREFETCH,
> [jrnieder] Nit: Is there a sort order for these? Should we establish an order
> early on (e.g. alphabetical)?

There _is_ an order, and maybe that should be up for debate.
This one is really about fetching new refs before (possibly)
deleting unreachable data or doing a full repack in the 'gc'
task. The rest of the tasks are after the 'gc' task (in an
unimportant order) because they are likely to be no-ops if the
'gc' task does work.

Of course, users can customize this order using the
--task=<task> options.

>>  	TASK_GC,
>>  	TASK_COMMIT_GRAPH,
> 
>> +test_expect_success 'prefetch multiple remotes' '
>> +	git clone . clone1 &&
>> +	git clone . clone2 &&
>> +	git remote add remote1 "file://$(pwd)/clone1" &&
>> +	git remote add remote2 "file://$(pwd)/clone2" &&
>> +	git -C clone1 switch -c one &&
>> +	git -C clone2 switch -c two &&
>> +	test_commit -C clone1 one &&
>> +	test_commit -C clone2 two &&
>> +	GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null &&
>> +	fetchargs="--prune --no-tags --no-write-fetch-head --refmap= --quiet" &&
>> +	test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\* <run-prefetch.txt &&

> [jrnieder] In practice, why were all the \\ needed? Trying to figure out
> where Git is using a shell that would need the * escaped and finding it
> hard to reason about.

It's the 'grep' way down inside test_subcommand that will
fail if it interprets these '*' incorrectly.

>> +	test_subcommand git fetch remote2 $fetchargs +refs/heads/\\*:refs/prefetch/remote2/\\* <run-prefetch.txt &&
>> +	test_path_is_missing .git/refs/remotes &&
>> +	test_cmp clone1/.git/refs/heads/one .git/refs/prefetch/remote1/one &&
>> +	test_cmp clone2/.git/refs/heads/two .git/refs/prefetch/remote2/two &&

> [jrnieder] Should we use test_cmp_rev instead to make compatible with
> packed-refs?

While that would be good, these are refs across two .git directories.

I suppose that I could fetch normally and check refs/remotes/remote1/one
versus refs/prefetch/remote1/one.

>> +	git log prefetch/remote1/one &&
>> +	git log prefetch/remote2/two

> [jonathantan] Why do we use 'git log' to check? I'm a little confused
> about what's going on; if you just want to check that the refs are
> present you could use 'git rev-parse' instead?

The main point is to demonstrate that we have the actual objects
in the current repository, not just refs storing object IDs that
don't actually exist in the object database. Does rev-parse check
that the object exists? (A quick check in my local repository seems
to say no.)

Reorganizing the test to work with test_cmp_rev results in the
following:

test_expect_success 'prefetch multiple remotes' '
	git clone . clone1 &&
	git clone . clone2 &&
	git remote add remote1 "file://$(pwd)/clone1" &&
	git remote add remote2 "file://$(pwd)/clone2" &&
	git -C clone1 switch -c one &&
	git -C clone2 switch -c two &&
	test_commit -C clone1 one &&
	test_commit -C clone2 two &&
	GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null &&
	fetchargs="--prune --no-tags --no-write-fetch-head --recurse-submodules=no --refmap= --quiet" &&
	test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\* <run-prefetch.txt &&
	test_subcommand git fetch remote2 $fetchargs +refs/heads/\\*:refs/prefetch/remote2/\\* <run-prefetch.txt &&
	test_path_is_missing .git/refs/remotes &&
	git log prefetch/remote1/one &&
	git log prefetch/remote2/two &&
	git fetch --all &&
	test_cmp_rev refs/remotes/remote1/one refs/prefetch/remote1/one &&
	test_cmp_rev refs/remotes/remote2/two refs/prefetch/remote2/two
'

Thanks,
-Stolee

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3] fetch: optionally allow disabling FETCH_HEAD update
  2020-08-14  1:13         ` Derrick Stolee
@ 2020-08-14  1:32           ` Junio C Hamano
  0 siblings, 0 replies; 66+ messages in thread
From: Junio C Hamano @ 2020-08-14  1:32 UTC (permalink / raw)
  To: Derrick Stolee
  Cc: Jonathan Nieder, Junio C Hamano via GitGitGadget, git,
	Derrick Stolee, Emily Shaffer

Derrick Stolee <stolee@gmail.com> writes:

>>  * So, it becomes much smaller by punting the whole configuration
>>    thing, as we do not need the extra code for config parsing and
>>    there is no need for code to override the user configuration when
>>    driving "git fetch" from "git pull".
>
> Sounds good. I'll incorporate this patch into my next version,
> except it seems you dropped this test:

Yup.  

As we are not touching "pull" at all, the test I removed would make
as much sense as a hypothetical one where its "git pull" is replaced
with "git cat-file" or any other unrelated subcommand, and that is
why I removed it.  But I am OK if you resurrect it---everybody thinks
"fetch" and "pull" are closely related after all.

Thanks.



> diff --git a/t/t5521-pull-options.sh b/t/t5521-pull-options.sh
> index 159afa7ac8..db1a381cd9 100755
> --- a/t/t5521-pull-options.sh
> +++ b/t/t5521-pull-options.sh
> @@ -85,6 +85,13 @@ test_expect_success 'git pull --cleanup errors early on invalid argument' '
>         test -s err)
>  '
>  
> +test_expect_success 'git pull --no-write-fetch-head fails' '
> +       mkdir clonedwfh &&
> +       (cd clonedwfh && git init &&
> +       test_expect_code 129 git pull --no-write-fetch-head "../parent" >out 2>err &&
> +       test_must_be_empty out &&
> +       test_i18ngrep "no-write-fetch-head" err)
> +'
>  
>  test_expect_success 'git pull --force' '
>         mkdir clonedoldstyle &&
>
> which I changed "test_must_fail" to "test_expect_code 129" to
> demonstrate that this is a usage error, not just any error.
>
> Thanks,
> -Stolee

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH 3/9] maintenance: add loose-objects task
  2020-08-12 23:10   ` Emily Shaffer
@ 2020-08-14  1:46     ` Derrick Stolee
  0 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee @ 2020-08-14  1:46 UTC (permalink / raw)
  To: Emily Shaffer, Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

On 8/12/2020 7:10 PM, Emily Shaffer wrote:
> On Thu, Aug 06, 2020 at 04:30:18PM +0000, Derrick Stolee via GitGitGadget wrote:
> 
>> diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
>> index bb0d5eded4..898aff4726 100644
>> --- a/Documentation/git-maintenance.txt
>> +++ b/Documentation/git-maintenance.txt
>> @@ -80,6 +80,17 @@ gc::
>>  	It can also be disruptive in some situations, as it deletes stale
>>  	data.
>>  
>> +loose-objects::
>> +	The `loose-objects` job cleans up loose objects and places them into
>> +	pack-files. In order to prevent race conditions with concurrent Git
>> +	commands, it follows a two-step process. First, it deletes any loose
>> +	objects that already exist in a pack-file; concurrent Git processes
>> +	will examine the pack-file for the object data instead of the loose
>> +	object. Second, it creates a new pack-file (starting with "loose-")
>> +	containing a batch of loose objects. The batch size is limited to 50
>> +	thousand objects to prevent the job from taking too long on a
>> +	repository with many loose objects.
> 
> [emily] What's not said is what happens to loose-* packfile. Does this
> get repacked and disappear, is it treated differently, etc?
> [jonathantan] This is treated the same as any other pack. Is there a
> reason to call it loose-*?

Auditing, mostly. When working with repositories that have
multiple pack-files as a rule, it is helpful to know what "kind"
of pack-file they are. I almost added a "repacked-" prefix to
the packs produced by 'git multi-pack-index repack'. It helps
to distinguish "reprocessed" data from "I got this from a 'clone'
or 'fetch'."

Of course, as these pack-files are repacked later, the prefixes
will get dropped. The name does give us some help when performing
diagnostics on a misbehaving repository. A pack directory filled
with many "loose-*.pack" files indicates that the 'loose-objects'
step was run many times without either 'gc' or 'incremental-repack'
coalescing those packs with delta compression.

> [jrnieder] It seems like unreachable objects will get stuck going in and
> out of this pack, right? unreachable loose obj -> loose-*.pack ->
> repack, unreachable becomes loose -> repeat

This is a good point. This task would probably interact poorly with
the 'gc' task in that regard. They are not intended to both be
enabled at the same time, but it might be good to point that out
directly in the documentation.

How does this sound?

 The `gc` task writes unreachable objects as loose objects to
 be cleaned up by a later step only if they are not re-added to
 a pack-file; for this reason it is not advisable to enable both
 the `loose-objects` and `gc` tasks at the same time.

>> +static int prune_packed(struct maintenance_opts *opts)
>> +{
>> +	struct child_process child = CHILD_PROCESS_INIT;
>> +
>> +	child.git_cmd = 1;
>> +	strvec_push(&child.args, "prune-packed");
>> +
>> +	if (opts->quiet)
>> +		strvec_push(&child.args, "--quiet");
>> +
>> +	return !!run_command(&child);

> [emily] Why not report the error code here to the caller? Is there a
> path to notify user of errors that require user intervention?
> [jrnieder] Some errors might be expected and some might not, so should
> we handle them differently?
> [emily] Probably makes more sense to revisit this in the far future when
> we teach 'git maintenance' to send us emails and flashing lights when
> our jobs fail, instead of worrying about it now :)
> [jrnieder] Imagine if we got exit 127 because the usage we are using is
> wrong - in that case, for example, we would want to BUG()

I was previously returning the exact error code, but received
feedback that these internal methods should have simpler return
values [1].

[1] https://lore.kernel.org/git/xmqq4kpyq8wh.fsf@gitster.c.googlers.com/

>> +static int write_loose_object_to_stdin(const struct object_id *oid,
>> +				       const char *path,
>> +				       void *data)
>> +{
>> +	struct write_loose_object_data *d = (struct write_loose_object_data *)data;

> [jrnieder] Since we are enlightened C developers, not C++ developers,
> you can skip the explicit cast.

Hm. I definitely _could_ but don't really want to. Perhaps I'm just
being pedantic, but I was just talking to someone today off-list that
they were disappointed that they couldn't compile Git in a C++ compiler
mainly because of these kinds of casting issues.

I was surprised the word "cast" does not appear anywhere in the
CodingGuidelines, because if this is a convention we want to follow,
then I have definitely been violating it for a *while*.
 
>> +++ b/t/t7900-maintenance.sh
>> @@ -83,4 +83,43 @@ test_expect_success 'prefetch multiple remotes' '
>>  	git log prefetch/remote2/two
>>  '
>>  
>> +test_expect_success 'loose-objects task' '

> [jrnieder] Unrelated to this change, this test makes me sad that we
> don't have better low-level test helpers to enable this kind of testing.> Makes me wish for something better :)

Do you mean you wish we had helpers for getting a repo
into a certain state of its object database? Or somehow
mocking the object database in-memory to provide more
unit-level testing? I don't understand what "something
better" looks like.

>> +	# Repack everything so we know the state of the object dir
>> +	git repack -adk &&
>> +
>> +	# Hack to stop maintenance from running during "git commit"
>> +	echo in use >.git/objects/maintenance.lock &&
>> +
>> +	# Assuming that "git commit" creates at least one loose object
>> +	test_commit create-loose-object &&
>> +	rm .git/objects/maintenance.lock &&
>> +
>> +	ls .git/objects >obj-dir-before &&
>> +	test_file_not_empty obj-dir-before &&
>> +	ls .git/objects/pack/*.pack >packs-before &&
>> +	test_line_count = 1 packs-before &&
>> +
>> +	# The first run creates a pack-file
>> +	# but does not delete loose objects.
>> +	git maintenance run --task=loose-objects &&
>> +	ls .git/objects >obj-dir-between &&
>> +	test_cmp obj-dir-before obj-dir-between &&
>> +	ls .git/objects/pack/*.pack >packs-between &&
>> +	test_line_count = 2 packs-between &&
>> +	ls .git/objects/pack/loose-*.pack >loose-packs &&
>> +	test_line_count = 1 loose-packs &&
>> +
>> +	# The second run deletes loose objects
>> +	# but does not create a pack-file.
>> +	git maintenance run --task=loose-objects &&
>> +	ls .git/objects >obj-dir-after &&
>> +	cat >expect <<-\EOF &&
>> +	info
>> +	pack
>> +	EOF
>> +	test_cmp expect obj-dir-after &&
>> +	ls .git/objects/pack/*.pack >packs-after &&
>> +	test_cmp packs-between packs-after
>> +'
>> +
> 


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks
  2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                   ` (8 preceding siblings ...)
  2020-08-06 16:30 ` [PATCH 9/9] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
@ 2020-08-18 14:25 ` Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
                     ` (9 more replies)
  9 siblings, 10 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee

This series is based on part I [2].

This patch series contains 9 patches that were going to be part of v4 of
ds/maintenance [1], but the discussion has gotten really long. To help, I'm
splitting out the portions that create and test the 'maintenance' builtin
from the additional tasks (prefetch, loose-objects, incremental-repack) that
can be brought in later.

[1] 
https://lore.kernel.org/git/pull.671.git.1594131695.gitgitgadget@gmail.com/
[2] 
https://lore.kernel.org/git/pull.695.git.1596728921.gitgitgadget@gmail.com/

As detailed in [2], the 'git maintenance run' subcommand will run certain
tasks based on config options or the --task= arguments. The --auto option
indicates to the task to only run based on some internal check that there
has been "enough" change in that domain to merit the work. In the case of
the 'gc' task, this also reduces the amount of work done. 

The new maintenance tasks in this series are:

 * 'loose-objects' : prune packed loose objects, then create a new pack from
   a batch of loose objects.
 * 'pack-files' : expire redundant packs from the multi-pack-index, then
   repack using the multi-pack-index's incremental repack strategy.
 * 'prefetch' : fetch from each remote, storing the refs in 'refs/prefetch/
   /'.

These tasks are all disabled by default, but can be enabled with config
options or run explicitly using "git maintenance run --task=". 

Since [2] replaced the 'git gc --auto' calls with 'git maintenance run
--auto' at the end of some Git commands, users could replace the 'gc' task
with these lighter-weight changes for foreground maintenance.

The 'git maintenance' builtin has a 'run' subcommand so it can be extended
later with subcommands that manage background maintenance, such as 'start'
or 'stop'. These are not the subject of this series, as it is important to
focus on the maintenance activities themselves. I have a WIP series for this
available at [3].

[3] https://github.com/gitgitgadget/git/pull/680

Updates since v1 (of this series)
=================================

 * PATCH 1 ("fetch: optionally allow disabling FETCH_HEAD update") was
   rewritten on-list. Getting a version out with this patch is the main
   reason for rolling a v2. (That, and Part I is re-rolled with a v2 and I
   want to make sure this series applies cleanly.)
   
   
 * The 'prefetch' and 'loose-objects' tasks had some review, but my proposed
   changes were not acked, so they may need another review.
   
   

UPDATES since v3 of [1]
=======================

 * The biggest change here is the use of "test_subcommand", based on
   Jonathan Nieder's approach. This requires having the exact command-line
   figured out, which now requires spelling out all --no- [quiet%7Cprogress] 
   options. I also added a bunch of "2>/dev/null" checks because of the
   isatty(2) calls. Without that, the behavior will change depending on
   whether the test is run with -x/-v or without.
   
   
 * The 0x7FFF/0x7FFFFFFF constant problem is fixed with an EXPENSIVE test
   that verifies it.
   
   
 * The option parsing has changed to use a local struct and pass that struct
   to the helper methods. This is instead of having a global singleton.
   
   

Thanks, -Stolee

Derrick Stolee (8):
  maintenance: add prefetch task
  maintenance: add loose-objects task
  maintenance: create auto condition for loose-objects
  midx: enable core.multiPackIndex by default
  midx: use start_delayed_progress()
  maintenance: add incremental-repack task
  maintenance: auto-size incremental-repack batch
  maintenance: add incremental-repack auto condition

Junio C Hamano (1):
  fetch: optionally allow disabling FETCH_HEAD update

 Documentation/config/core.txt        |   4 +-
 Documentation/config/maintenance.txt |  18 ++
 Documentation/fetch-options.txt      |   9 +
 Documentation/git-maintenance.txt    |  45 ++++
 builtin/fetch.c                      |  15 +-
 builtin/gc.c                         | 363 +++++++++++++++++++++++++++
 midx.c                               |  23 +-
 midx.h                               |   1 +
 repo-settings.c                      |   6 +
 repository.h                         |   2 +
 t/t5319-multi-pack-index.sh          |  15 +-
 t/t5510-fetch.sh                     |  15 +-
 t/t5521-pull-options.sh              |   7 +
 t/t7900-maintenance.sh               | 191 ++++++++++++++
 14 files changed, 686 insertions(+), 28 deletions(-)


base-commit: 46fbe161aa154de9406117ee916b1bd5f549905c
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-696%2Fderrickstolee%2Fmaintenance%2Fgc-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-696/derrickstolee/maintenance/gc-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/696

Range-diff vs v1:

  1:  83401c5200 !  1:  f3bc0b2d92 fetch: optionally allow disabling FETCH_HEAD update
     @@ Commit message
          refs (e.g. you fetch and then merge origin/branchname separately),
          you can get away with having no FETCH_HEAD at all.
      
     -    Teach "git fetch" a command line option "--[no-]write-fetch-head"
     -    and "fetch.writeFetchHEAD" configuration variable.  Without either,
     -    the default is to write FETCH_HEAD, and the usual rule that the
     -    command line option defeats configured default applies.
     +    Teach "git fetch" a command line option "--[no-]write-fetch-head".
     +    The default is to write FETCH_HEAD, and the option is primarily
     +    meant to be used with the "--no-" prefix to override this default,
     +    because there is no matching fetch.writeFetchHEAD configuration
     +    variable to flip the default to off (in which case, the positive
     +    form may become necessary to defeat it).
      
          Note that under "--dry-run" mode, FETCH_HEAD is never written;
          otherwise you'd see list of objects in the file that you do not
          actually have.  Passing `--write-fetch-head` does not force `git
          fetch` to write the file.
      
     -    Also note that this option is explicitly passed when "git pull"
     -    internally invokes "git fetch", so that those who configured their
     -    "git fetch" not to write FETCH_HEAD would not be able to break the
     -    cooperation between these two commands.  "git pull" must see what
     -    "git fetch" got recorded in FETCH_HEAD to work correctly.
     -
     -    Signed-off-by: Junio C Hamano <gitster@pobox.com>
          Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
     -
     - ## Documentation/config/fetch.txt ##
     -@@ Documentation/config/fetch.txt: fetch.writeCommitGraph::
     - 	merge and the write may take longer. Having an updated commit-graph
     - 	file helps performance of many Git commands, including `git merge-base`,
     - 	`git push -f`, and `git log --graph`. Defaults to false.
     -+
     -+fetch.writeFetchHEAD::
     -+	Setting it to false tells `git fetch` not to write the list
     -+	of remote refs fetched in the `FETCH_HEAD` file directly
     -+	under `$GIT_DIR`.  Can be countermanded from the command
     -+	line with the `--[no-]write-fetch-head` option.  Defaults to
     -+	true.
     +    Signed-off-by: Junio C Hamano <gitster@pobox.com>
      
       ## Documentation/fetch-options.txt ##
      @@ Documentation/fetch-options.txt: documented in linkgit:git-config[1].
     @@ Documentation/fetch-options.txt: documented in linkgit:git-config[1].
      +ifndef::git-pull[]
      +--[no-]write-fetch-head::
      +	Write the list of remote refs fetched in the `FETCH_HEAD`
     -+	file directly under `$GIT_DIR`.  This is the default unless
     -+	the configuration variable `fetch.writeFetchHEAD` is set to
     -+	false.  Passing `--no-write-fetch-head` from the command
     -+	line tells Git not to write the file.  Under `--dry-run`
     -+	option, the file is never written.
     ++	file directly under `$GIT_DIR`.  This is the default.
     ++	Passing `--no-write-fetch-head` from the command line tells
     ++	Git not to write the file.  Under `--dry-run` option, the
     ++	file is never written.
      +endif::git-pull[]
      +
       -f::
     @@ builtin/fetch.c: static int prune_tags = -1; /* unspecified */
       static int verbosity, deepen_relative, set_upstream;
       static int progress = -1;
       static int enable_auto_gc = 1;
     -@@ builtin/fetch.c: static int git_fetch_config(const char *k, const char *v, void *cb)
     - 		return 0;
     - 	}
     - 
     -+	if (!strcmp(k, "fetch.writefetchhead")) {
     -+		write_fetch_head = git_config_bool(k, v);
     -+		return 0;
     -+	}
     - 	return git_default_config(k, v, cb);
     - }
     - 
      @@ builtin/fetch.c: static struct option builtin_fetch_options[] = {
       		    PARSE_OPT_OPTARG, option_fetch_parse_recurse_submodules),
       	OPT_BOOL(0, "dry-run", &dry_run,
     @@ builtin/fetch.c: int cmd_fetch(int argc, const char **argv, const char *prefix)
       		if (argc == 1)
       			die(_("fetch --all does not take a repository argument"));
      
     - ## builtin/pull.c ##
     -@@ builtin/pull.c: static int run_fetch(const char *repo, const char **refspecs)
     - 	struct strvec args = STRVEC_INIT;
     - 	int ret;
     - 
     --	strvec_pushl(&args, "fetch", "--update-head-ok", NULL);
     -+	strvec_pushl(&args, "fetch", "--update-head-ok",
     -+		     "--write-fetch-head", NULL);
     - 
     - 	/* Shared options */
     - 	argv_push_verbosity(&args);
     -
       ## t/t5510-fetch.sh ##
      @@ t/t5510-fetch.sh: test_expect_success 'fetch into the current branch with --update-head-ok' '
       
     @@ t/t5510-fetch.sh: test_expect_success 'fetch into the current branch with --upda
      +	git fetch --dry-run --write-fetch-head . &&
      +	! test -f .git/FETCH_HEAD
      +'
     -+
     -+test_expect_success 'fetch.writeFetchHEAD and FETCH_HEAD' '
     -+	rm -f .git/FETCH_HEAD &&
     -+	git -c fetch.writeFetchHEAD=no fetch . &&
     -+	! test -f .git/FETCH_HEAD
     -+'
     -+
     -+test_expect_success 'fetch.writeFetchHEAD gets defeated by --dry-run' '
     -+	rm -f .git/FETCH_HEAD &&
     -+	git -c fetch.writeFetchHEAD=yes fetch --dry-run . &&
     -+	! test -f .git/FETCH_HEAD
     -+'
     -+
     -+test_expect_success 'fetch.writeFetchHEAD and --no-write-fetch-head' '
     -+	rm -f .git/FETCH_HEAD &&
     -+	git -c fetch.writeFetchHEAD=yes fetch --no-write-fetch-head . &&
     -+	! test -f .git/FETCH_HEAD
     -+'
     -+
     -+test_expect_success 'fetch.writeFetchHEAD and --write-fetch-head' '
     -+	rm -f .git/FETCH_HEAD &&
     -+	git -c fetch.writeFetchHEAD=no fetch --write-fetch-head . &&
     -+	test -f .git/FETCH_HEAD
     -+'
      +
       test_expect_success "should be able to fetch with duplicate refspecs" '
       	mkdir dups &&
       	(
      
       ## t/t5521-pull-options.sh ##
     -@@ t/t5521-pull-options.sh: test_expect_success 'git pull -q -v --no-rebase' '
     - 	test_must_be_empty out &&
     - 	test -s err)
     - '
     -+
     - test_expect_success 'git pull --cleanup errors early on invalid argument' '
     - 	mkdir clonedcleanup &&
     - 	(cd clonedcleanup && git init &&
      @@ t/t5521-pull-options.sh: test_expect_success 'git pull --cleanup errors early on invalid argument' '
       	test -s err)
       '
     @@ t/t5521-pull-options.sh: test_expect_success 'git pull --cleanup errors early on
      +test_expect_success 'git pull --no-write-fetch-head fails' '
      +	mkdir clonedwfh &&
      +	(cd clonedwfh && git init &&
     -+	test_must_fail git pull --no-write-fetch-head "../parent" >out 2>err &&
     ++	test_expect_code 129 git pull --no-write-fetch-head "../parent" >out 2>err &&
      +	test_must_be_empty out &&
      +	test_i18ngrep "no-write-fetch-head" err)
     -+'
     -+
     -+test_expect_success 'git pull succeeds with fetch.writeFetchHEAD=false' '
     -+	mkdir clonedwfhconfig &&
     -+	(cd clonedwfhconfig && git init &&
     -+	git config fetch.writeFetchHEAD false &&
     -+	git pull "../parent" >out 2>err &&
     -+	grep FETCH_HEAD err)
      +'
       
       test_expect_success 'git pull --force' '
  2:  85118ed5f1 !  2:  8779c6c20d maintenance: add prefetch task
     @@ Documentation/git-maintenance.txt: since it will not expire `.graph` files that
      +any object transfer.
      +
       gc::
     - 	Cleanup unnecessary files and optimize the local repository. "GC"
     + 	Clean up unnecessary files and optimize the local repository. "GC"
       	stands for "garbage collection," but this task performs many
      
       ## builtin/gc.c ##
     @@ builtin/gc.c: static int maintenance_task_commit_graph(struct maintenance_opts *
      +
      +	child.git_cmd = 1;
      +	strvec_pushl(&child.args, "fetch", remote, "--prune", "--no-tags",
     -+		     "--no-write-fetch-head", "--refmap=", NULL);
     ++		     "--no-write-fetch-head", "--recurse-submodules=no",
     ++		     "--refmap=", NULL);
      +
      +	if (opts->quiet)
      +		strvec_push(&child.args, "--quiet");
     @@ builtin/gc.c: static int maintenance_task_commit_graph(struct maintenance_opts *
      +	return !!run_command(&child);
      +}
      +
     -+static int fill_each_remote(struct remote *remote, void *cbdata)
     ++static int append_remote(struct remote *remote, void *cbdata)
      +{
      +	struct string_list *remotes = (struct string_list *)cbdata;
      +
     @@ builtin/gc.c: static int maintenance_task_commit_graph(struct maintenance_opts *
      +	struct string_list_item *item;
      +	struct string_list remotes = STRING_LIST_INIT_DUP;
      +
     -+	if (for_each_remote(fill_each_remote, &remotes)) {
     ++	if (for_each_remote(append_remote, &remotes)) {
      +		error(_("failed to fill remotes"));
      +		result = 1;
      +		goto cleanup;
      +	}
      +
     -+	for (item = remotes.items;
     -+	     item && item < remotes.items + remotes.nr;
     -+	     item++)
     ++	for_each_string_list_item(item, &remotes)
      +		result |= fetch_remote(item->string, opts);
      +
      +cleanup:
     @@ t/t7900-maintenance.sh: test_expect_success 'run --task duplicate' '
      +	test_commit -C clone1 one &&
      +	test_commit -C clone2 two &&
      +	GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null &&
     -+	fetchargs="--prune --no-tags --no-write-fetch-head --refmap= --quiet" &&
     ++	fetchargs="--prune --no-tags --no-write-fetch-head --recurse-submodules=no --refmap= --quiet" &&
      +	test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\* <run-prefetch.txt &&
      +	test_subcommand git fetch remote2 $fetchargs +refs/heads/\\*:refs/prefetch/remote2/\\* <run-prefetch.txt &&
      +	test_path_is_missing .git/refs/remotes &&
     -+	test_cmp clone1/.git/refs/heads/one .git/refs/prefetch/remote1/one &&
     -+	test_cmp clone2/.git/refs/heads/two .git/refs/prefetch/remote2/two &&
      +	git log prefetch/remote1/one &&
     -+	git log prefetch/remote2/two
     ++	git log prefetch/remote2/two &&
     ++	git fetch --all &&
     ++	test_cmp_rev refs/remotes/remote1/one refs/prefetch/remote1/one &&
     ++	test_cmp_rev refs/remotes/remote2/two refs/prefetch/remote2/two
      +'
      +
       test_done
  3:  621375a3c9 !  3:  4fa9d298b9 maintenance: add loose-objects task
     @@ Commit message
      
       ## Documentation/git-maintenance.txt ##
      @@ Documentation/git-maintenance.txt: gc::
     - 	It can also be disruptive in some situations, as it deletes stale
     - 	data.
     + 	be disruptive in some situations, as it deletes stale data. See
     + 	linkgit:git-gc[1] for more details on garbage collection in Git.
       
      +loose-objects::
      +	The `loose-objects` job cleans up loose objects and places them into
     @@ Documentation/git-maintenance.txt: gc::
      +	object. Second, it creates a new pack-file (starting with "loose-")
      +	containing a batch of loose objects. The batch size is limited to 50
      +	thousand objects to prevent the job from taking too long on a
     -+	repository with many loose objects.
     ++	repository with many loose objects. The `gc` task writes unreachable
     ++	objects as loose objects to be cleaned up by a later step only if
     ++	they are not re-added to a pack-file; for this reason it is not
     ++	advisable to enable both the `loose-objects` and `gc` tasks at the
     ++	same time.
      +
       OPTIONS
       -------
     @@ builtin/gc.c: static struct maintenance_task tasks[] = {
      
       ## t/t7900-maintenance.sh ##
      @@ t/t7900-maintenance.sh: test_expect_success 'prefetch multiple remotes' '
     - 	git log prefetch/remote2/two
     + 	test_cmp_rev refs/remotes/remote2/two refs/prefetch/remote2/two
       '
       
      +test_expect_success 'loose-objects task' '
  4:  e787403ea7 =  4:  3432bc3167 maintenance: create auto condition for loose-objects
  5:  37e59b1a8d =  5:  0ee2434bdb midx: enable core.multiPackIndex by default
  6:  aba087f663 =  6:  e157ea8dd7 midx: use start_delayed_progress()
  7:  68727c555b !  7:  a8d956dad6 maintenance: add incremental-repack task
     @@ Commit message
      
       ## Documentation/git-maintenance.txt ##
      @@ Documentation/git-maintenance.txt: loose-objects::
     - 	thousand objects to prevent the job from taking too long on a
     - 	repository with many loose objects.
     + 	advisable to enable both the `loose-objects` and `gc` tasks at the
     + 	same time.
       
      +incremental-repack::
      +	The `incremental-repack` job repacks the object directory
  8:  c3487fb8e3 =  8:  f0e7276755 maintenance: auto-size incremental-repack batch
  9:  407c123c51 !  9:  5659a23ad5 maintenance: add incremental-repack auto condition
     @@ builtin/gc.c: static struct maintenance_task tasks[] = {
       		"gc",
      
       ## t/t7900-maintenance.sh ##
     -@@ t/t7900-maintenance.sh: test_expect_success 'incremental-repack task' '
     - '
     - 
     - test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
     -+
     - 	for i in $(test_seq 1 5)
     - 	do
     - 		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
      @@ t/t7900-maintenance.sh: test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
       		 --no-progress --batch-size=2147483647 <run-2g.txt
       '

-- 
gitgitgadget

^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 1/9] fetch: optionally allow disabling FETCH_HEAD update
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
@ 2020-08-18 14:25   ` Junio C Hamano via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 2/9] maintenance: add prefetch task Derrick Stolee via GitGitGadget
                     ` (8 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Junio C Hamano via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Junio C Hamano

From: Junio C Hamano <gitster@pobox.com>

If you run fetch but record the result in remote-tracking branches,
and either if you do nothing with the fetched refs (e.g. you are
merely mirroring) or if you always work from the remote-tracking
refs (e.g. you fetch and then merge origin/branchname separately),
you can get away with having no FETCH_HEAD at all.

Teach "git fetch" a command line option "--[no-]write-fetch-head".
The default is to write FETCH_HEAD, and the option is primarily
meant to be used with the "--no-" prefix to override this default,
because there is no matching fetch.writeFetchHEAD configuration
variable to flip the default to off (in which case, the positive
form may become necessary to defeat it).

Note that under "--dry-run" mode, FETCH_HEAD is never written;
otherwise you'd see list of objects in the file that you do not
actually have.  Passing `--write-fetch-head` does not force `git
fetch` to write the file.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/fetch-options.txt |  9 +++++++++
 builtin/fetch.c                 | 15 ++++++++++++---
 t/t5510-fetch.sh                | 15 +++++++++++++--
 t/t5521-pull-options.sh         |  7 +++++++
 4 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/Documentation/fetch-options.txt b/Documentation/fetch-options.txt
index 495bc8ab5a..b65a758661 100644
--- a/Documentation/fetch-options.txt
+++ b/Documentation/fetch-options.txt
@@ -64,6 +64,15 @@ documented in linkgit:git-config[1].
 --dry-run::
 	Show what would be done, without making any changes.
 
+ifndef::git-pull[]
+--[no-]write-fetch-head::
+	Write the list of remote refs fetched in the `FETCH_HEAD`
+	file directly under `$GIT_DIR`.  This is the default.
+	Passing `--no-write-fetch-head` from the command line tells
+	Git not to write the file.  Under `--dry-run` option, the
+	file is never written.
+endif::git-pull[]
+
 -f::
 --force::
 	When 'git fetch' is used with `<src>:<dst>` refspec it may
diff --git a/builtin/fetch.c b/builtin/fetch.c
index c8b9366d3c..cb38e6f5ec 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -56,6 +56,7 @@ static int prune_tags = -1; /* unspecified */
 #define PRUNE_TAGS_BY_DEFAULT 0 /* do we prune tags by default? */
 
 static int all, append, dry_run, force, keep, multiple, update_head_ok;
+static int write_fetch_head = 1;
 static int verbosity, deepen_relative, set_upstream;
 static int progress = -1;
 static int enable_auto_gc = 1;
@@ -162,6 +163,8 @@ static struct option builtin_fetch_options[] = {
 		    PARSE_OPT_OPTARG, option_fetch_parse_recurse_submodules),
 	OPT_BOOL(0, "dry-run", &dry_run,
 		 N_("dry run")),
+	OPT_BOOL(0, "write-fetch-head", &write_fetch_head,
+		 N_("write fetched references to the FETCH_HEAD file")),
 	OPT_BOOL('k', "keep", &keep, N_("keep downloaded pack")),
 	OPT_BOOL('u', "update-head-ok", &update_head_ok,
 		    N_("allow updating of HEAD ref")),
@@ -895,7 +898,9 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 	const char *what, *kind;
 	struct ref *rm;
 	char *url;
-	const char *filename = dry_run ? "/dev/null" : git_path_fetch_head(the_repository);
+	const char *filename = (!write_fetch_head
+				? "/dev/null"
+				: git_path_fetch_head(the_repository));
 	int want_status;
 	int summary_width = transport_summary_width(ref_map);
 
@@ -1329,7 +1334,7 @@ static int do_fetch(struct transport *transport,
 	}
 
 	/* if not appending, truncate FETCH_HEAD */
-	if (!append && !dry_run) {
+	if (!append && write_fetch_head) {
 		retcode = truncate_fetch_head();
 		if (retcode)
 			goto cleanup;
@@ -1596,7 +1601,7 @@ static int fetch_multiple(struct string_list *list, int max_children)
 	int i, result = 0;
 	struct strvec argv = STRVEC_INIT;
 
-	if (!append && !dry_run) {
+	if (!append && write_fetch_head) {
 		int errcode = truncate_fetch_head();
 		if (errcode)
 			return errcode;
@@ -1797,6 +1802,10 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	if (depth || deepen_since || deepen_not.nr)
 		deepen = 1;
 
+	/* FETCH_HEAD never gets updated in --dry-run mode */
+	if (dry_run)
+		write_fetch_head = 0;
+
 	if (all) {
 		if (argc == 1)
 			die(_("fetch --all does not take a repository argument"));
diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
index 9850ecde5d..5bd1f953af 100755
--- a/t/t5510-fetch.sh
+++ b/t/t5510-fetch.sh
@@ -539,13 +539,24 @@ test_expect_success 'fetch into the current branch with --update-head-ok' '
 
 '
 
-test_expect_success 'fetch --dry-run' '
-
+test_expect_success 'fetch --dry-run does not touch FETCH_HEAD' '
 	rm -f .git/FETCH_HEAD &&
 	git fetch --dry-run . &&
 	! test -f .git/FETCH_HEAD
 '
 
+test_expect_success '--no-write-fetch-head does not touch FETCH_HEAD' '
+	rm -f .git/FETCH_HEAD &&
+	git fetch --no-write-fetch-head . &&
+	! test -f .git/FETCH_HEAD
+'
+
+test_expect_success '--write-fetch-head gets defeated by --dry-run' '
+	rm -f .git/FETCH_HEAD &&
+	git fetch --dry-run --write-fetch-head . &&
+	! test -f .git/FETCH_HEAD
+'
+
 test_expect_success "should be able to fetch with duplicate refspecs" '
 	mkdir dups &&
 	(
diff --git a/t/t5521-pull-options.sh b/t/t5521-pull-options.sh
index 159afa7ac8..db1a381cd9 100755
--- a/t/t5521-pull-options.sh
+++ b/t/t5521-pull-options.sh
@@ -85,6 +85,13 @@ test_expect_success 'git pull --cleanup errors early on invalid argument' '
 	test -s err)
 '
 
+test_expect_success 'git pull --no-write-fetch-head fails' '
+	mkdir clonedwfh &&
+	(cd clonedwfh && git init &&
+	test_expect_code 129 git pull --no-write-fetch-head "../parent" >out 2>err &&
+	test_must_be_empty out &&
+	test_i18ngrep "no-write-fetch-head" err)
+'
 
 test_expect_success 'git pull --force' '
 	mkdir clonedoldstyle &&
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 2/9] maintenance: add prefetch task
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
@ 2020-08-18 14:25   ` Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 3/9] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
                     ` (7 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

When working with very large repositories, an incremental 'git fetch'
command can download a large amount of data. If there are many other
users pushing to a common repo, then this data can rival the initial
pack-file size of a 'git clone' of a medium-size repo.

Users may want to keep the data on their local repos as close as
possible to the data on the remote repos by fetching periodically in
the background. This can break up a large daily fetch into several
smaller hourly fetches.

The task is called "prefetch" because it is work done in advance
of a foreground fetch to make that 'git fetch' command much faster.

However, if we simply ran 'git fetch <remote>' in the background,
then the user running a foregroudn 'git fetch <remote>' would lose
some important feedback when a new branch appears or an existing
branch updates. This is especially true if a remote branch is
force-updated and this isn't noticed by the user because it occurred
in the background. Further, the functionality of 'git push
--force-with-lease' becomes suspect.

When running 'git fetch <remote> <options>' in the background, use
the following options for careful updating:

1. --no-tags prevents getting a new tag when a user wants to see
   the new tags appear in their foreground fetches.

2. --refmap= removes the configured refspec which usually updates
   refs/remotes/<remote>/* with the refs advertised by the remote.
   While this looks confusing, this was documented and tested by
   b40a50264ac (fetch: document and test --refmap="", 2020-01-21),
   including this sentence in the documentation:

	Providing an empty `<refspec>` to the `--refmap` option
	causes Git to ignore the configured refspecs and rely
	entirely on the refspecs supplied as command-line arguments.

3. By adding a new refspec "+refs/heads/*:refs/prefetch/<remote>/*"
   we can ensure that we actually load the new values somewhere in
   our refspace while not updating refs/heads or refs/remotes. By
   storing these refs here, the commit-graph job will update the
   commit-graph with the commits from these hidden refs.

4. --prune will delete the refs/prefetch/<remote> refs that no
   longer appear on the remote.

5. --no-write-fetch-head prevents updating FETCH_HEAD.

We've been using this step as a critical background job in Scalar
[1] (and VFS for Git). This solved a pain point that was showing up
in user reports: fetching was a pain! Users do not like waiting to
download the data that was created while they were away from their
machines. After implementing background fetch, the foreground fetch
commands sped up significantly because they mostly just update refs
and download a small amount of new data. The effect is especially
dramatic when paried with --no-show-forced-udpates (through
fetch.showForcedUpdates=false).

[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/FetchStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 15 +++++++++
 builtin/gc.c                      | 51 +++++++++++++++++++++++++++++++
 t/t7900-maintenance.sh            | 26 ++++++++++++++++
 3 files changed, 92 insertions(+)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 9af08c644f..e82799ccff 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -50,6 +50,21 @@ since it will not expire `.graph` files that were in the previous
 `commit-graph-chain` file. They will be deleted by a later run based on
 the expiration delay.
 
+prefetch::
+	The `prefetch` task updates the object directory with the latest
+	objects from all registered remotes. For each remote, a `git fetch`
+	command is run. The refmap is custom to avoid updating local or remote
+	branches (those in `refs/heads` or `refs/remotes`). Instead, the
+	remote refs are stored in `refs/prefetch/<remote>/`. Also, tags are
+	not updated.
++
+This is done to avoid disrupting the remote-tracking branches. The end users
+expect these refs to stay unmoved unless they initiate a fetch.  With prefetch
+task, however, the objects necessary to complete a later real fetch would
+already be obtained, so the real fetch would go faster.  In the ideal case,
+it will just become an update to bunch of remote-tracking branches without
+any object transfer.
+
 gc::
 	Clean up unnecessary files and optimize the local repository. "GC"
 	stands for "garbage collection," but this task performs many
diff --git a/builtin/gc.c b/builtin/gc.c
index 3fdb08655c..2ac08cc740 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -29,6 +29,7 @@
 #include "tree.h"
 #include "promisor-remote.h"
 #include "refs.h"
+#include "remote.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -843,6 +844,51 @@ static int maintenance_task_commit_graph(struct maintenance_opts *opts)
 	return 1;
 }
 
+static int fetch_remote(const char *remote, struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "fetch", remote, "--prune", "--no-tags",
+		     "--no-write-fetch-head", "--recurse-submodules=no",
+		     "--refmap=", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--quiet");
+
+	strvec_pushf(&child.args, "+refs/heads/*:refs/prefetch/%s/*", remote);
+
+	return !!run_command(&child);
+}
+
+static int append_remote(struct remote *remote, void *cbdata)
+{
+	struct string_list *remotes = (struct string_list *)cbdata;
+
+	string_list_append(remotes, remote->name);
+	return 0;
+}
+
+static int maintenance_task_prefetch(struct maintenance_opts *opts)
+{
+	int result = 0;
+	struct string_list_item *item;
+	struct string_list remotes = STRING_LIST_INIT_DUP;
+
+	if (for_each_remote(append_remote, &remotes)) {
+		error(_("failed to fill remotes"));
+		result = 1;
+		goto cleanup;
+	}
+
+	for_each_string_list_item(item, &remotes)
+		result |= fetch_remote(item->string, opts);
+
+cleanup:
+	string_list_clear(&remotes, 0);
+	return result;
+}
+
 static int maintenance_task_gc(struct maintenance_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -880,6 +926,7 @@ struct maintenance_task {
 };
 
 enum maintenance_task_label {
+	TASK_PREFETCH,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -888,6 +935,10 @@ enum maintenance_task_label {
 };
 
 static struct maintenance_task tasks[] = {
+	[TASK_PREFETCH] = {
+		"prefetch",
+		maintenance_task_prefetch,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 4f6a04ddb1..0bade09c43 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -60,4 +60,30 @@ test_expect_success 'run --task duplicate' '
 	test_i18ngrep "cannot be selected multiple times" err
 '
 
+test_expect_success 'run --task=prefetch with no remotes' '
+	git maintenance run --task=prefetch 2>err &&
+	test_must_be_empty err
+'
+
+test_expect_success 'prefetch multiple remotes' '
+	git clone . clone1 &&
+	git clone . clone2 &&
+	git remote add remote1 "file://$(pwd)/clone1" &&
+	git remote add remote2 "file://$(pwd)/clone2" &&
+	git -C clone1 switch -c one &&
+	git -C clone2 switch -c two &&
+	test_commit -C clone1 one &&
+	test_commit -C clone2 two &&
+	GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null &&
+	fetchargs="--prune --no-tags --no-write-fetch-head --recurse-submodules=no --refmap= --quiet" &&
+	test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\* <run-prefetch.txt &&
+	test_subcommand git fetch remote2 $fetchargs +refs/heads/\\*:refs/prefetch/remote2/\\* <run-prefetch.txt &&
+	test_path_is_missing .git/refs/remotes &&
+	git log prefetch/remote1/one &&
+	git log prefetch/remote2/two &&
+	git fetch --all &&
+	test_cmp_rev refs/remotes/remote1/one refs/prefetch/remote1/one &&
+	test_cmp_rev refs/remotes/remote2/two refs/prefetch/remote2/two
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 3/9] maintenance: add loose-objects task
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 2/9] maintenance: add prefetch task Derrick Stolee via GitGitGadget
@ 2020-08-18 14:25   ` Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 4/9] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
                     ` (6 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

One goal of background maintenance jobs is to allow a user to
disable auto-gc (gc.auto=0) but keep their repository in a clean
state. Without any cleanup, loose objects will clutter the object
database and slow operations. In addition, the loose objects will
take up extra space because they are not stored with deltas against
similar objects.

Create a 'loose-objects' task for the 'git maintenance run' command.
This helps clean up loose objects without disrupting concurrent Git
commands using the following sequence of events:

1. Run 'git prune-packed' to delete any loose objects that exist
   in a pack-file. Concurrent commands will prefer the packed
   version of the object to the loose version. (Of course, there
   are exceptions for commands that specifically care about the
   location of an object. These are rare for a user to run on
   purpose, and we hope a user that has selected background
   maintenance will not be trying to do foreground maintenance.)

2. Run 'git pack-objects' on a batch of loose objects. These
   objects are grouped by scanning the loose object directories in
   lexicographic order until listing all loose objects -or-
   reaching 50,000 objects. This is more than enough if the loose
   objects are created only by a user doing normal development.
   We noticed users with _millions_ of loose objects because VFS
   for Git downloads blobs on-demand when a file read operation
   requires populating a virtual file. This has potential of
   happening in partial clones if someone runs 'git grep' or
   otherwise evades the batch-download feature for requesting
   promisor objects.

This step is based on a similar step in Scalar [1] and VFS for Git.
[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/LooseObjectsStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 15 +++++
 builtin/gc.c                      | 97 +++++++++++++++++++++++++++++++
 t/t7900-maintenance.sh            | 39 +++++++++++++
 3 files changed, 151 insertions(+)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index e82799ccff..85205b5bb9 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -73,6 +73,21 @@ gc::
 	be disruptive in some situations, as it deletes stale data. See
 	linkgit:git-gc[1] for more details on garbage collection in Git.
 
+loose-objects::
+	The `loose-objects` job cleans up loose objects and places them into
+	pack-files. In order to prevent race conditions with concurrent Git
+	commands, it follows a two-step process. First, it deletes any loose
+	objects that already exist in a pack-file; concurrent Git processes
+	will examine the pack-file for the object data instead of the loose
+	object. Second, it creates a new pack-file (starting with "loose-")
+	containing a batch of loose objects. The batch size is limited to 50
+	thousand objects to prevent the job from taking too long on a
+	repository with many loose objects. The `gc` task writes unreachable
+	objects as loose objects to be cleaned up by a later step only if
+	they are not re-added to a pack-file; for this reason it is not
+	advisable to enable both the `loose-objects` and `gc` tasks at the
+	same time.
+
 OPTIONS
 -------
 --auto::
diff --git a/builtin/gc.c b/builtin/gc.c
index 2ac08cc740..39ea590b5a 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -907,6 +907,98 @@ static int maintenance_task_gc(struct maintenance_opts *opts)
 	return run_command(&child);
 }
 
+static int prune_packed(struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_push(&child.args, "prune-packed");
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--quiet");
+
+	return !!run_command(&child);
+}
+
+struct write_loose_object_data {
+	FILE *in;
+	int count;
+	int batch_size;
+};
+
+static int bail_on_loose(const struct object_id *oid,
+			 const char *path,
+			 void *data)
+{
+	return 1;
+}
+
+static int write_loose_object_to_stdin(const struct object_id *oid,
+				       const char *path,
+				       void *data)
+{
+	struct write_loose_object_data *d = (struct write_loose_object_data *)data;
+
+	fprintf(d->in, "%s\n", oid_to_hex(oid));
+
+	return ++(d->count) > d->batch_size;
+}
+
+static int pack_loose(struct maintenance_opts *opts)
+{
+	struct repository *r = the_repository;
+	int result = 0;
+	struct write_loose_object_data data;
+	struct child_process pack_proc = CHILD_PROCESS_INIT;
+
+	/*
+	 * Do not start pack-objects process
+	 * if there are no loose objects.
+	 */
+	if (!for_each_loose_file_in_objdir(r->objects->odb->path,
+					   bail_on_loose,
+					   NULL, NULL, NULL))
+		return 0;
+
+	pack_proc.git_cmd = 1;
+
+	strvec_push(&pack_proc.args, "pack-objects");
+	if (opts->quiet)
+		strvec_push(&pack_proc.args, "--quiet");
+	strvec_pushf(&pack_proc.args, "%s/pack/loose", r->objects->odb->path);
+
+	pack_proc.in = -1;
+
+	if (start_command(&pack_proc)) {
+		error(_("failed to start 'git pack-objects' process"));
+		return 1;
+	}
+
+	data.in = xfdopen(pack_proc.in, "w");
+	data.count = 0;
+	data.batch_size = 50000;
+
+	for_each_loose_file_in_objdir(r->objects->odb->path,
+				      write_loose_object_to_stdin,
+				      NULL,
+				      NULL,
+				      &data);
+
+	fclose(data.in);
+
+	if (finish_command(&pack_proc)) {
+		error(_("failed to finish 'git pack-objects' process"));
+		result = 1;
+	}
+
+	return result;
+}
+
+static int maintenance_task_loose_objects(struct maintenance_opts *opts)
+{
+	return prune_packed(opts) || pack_loose(opts);
+}
+
 typedef int maintenance_task_fn(struct maintenance_opts *opts);
 
 /*
@@ -927,6 +1019,7 @@ struct maintenance_task {
 
 enum maintenance_task_label {
 	TASK_PREFETCH,
+	TASK_LOOSE_OBJECTS,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -939,6 +1032,10 @@ static struct maintenance_task tasks[] = {
 		"prefetch",
 		maintenance_task_prefetch,
 	},
+	[TASK_LOOSE_OBJECTS] = {
+		"loose-objects",
+		maintenance_task_loose_objects,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 0bade09c43..2e9e369786 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -86,4 +86,43 @@ test_expect_success 'prefetch multiple remotes' '
 	test_cmp_rev refs/remotes/remote2/two refs/prefetch/remote2/two
 '
 
+test_expect_success 'loose-objects task' '
+	# Repack everything so we know the state of the object dir
+	git repack -adk &&
+
+	# Hack to stop maintenance from running during "git commit"
+	echo in use >.git/objects/maintenance.lock &&
+
+	# Assuming that "git commit" creates at least one loose object
+	test_commit create-loose-object &&
+	rm .git/objects/maintenance.lock &&
+
+	ls .git/objects >obj-dir-before &&
+	test_file_not_empty obj-dir-before &&
+	ls .git/objects/pack/*.pack >packs-before &&
+	test_line_count = 1 packs-before &&
+
+	# The first run creates a pack-file
+	# but does not delete loose objects.
+	git maintenance run --task=loose-objects &&
+	ls .git/objects >obj-dir-between &&
+	test_cmp obj-dir-before obj-dir-between &&
+	ls .git/objects/pack/*.pack >packs-between &&
+	test_line_count = 2 packs-between &&
+	ls .git/objects/pack/loose-*.pack >loose-packs &&
+	test_line_count = 1 loose-packs &&
+
+	# The second run deletes loose objects
+	# but does not create a pack-file.
+	git maintenance run --task=loose-objects &&
+	ls .git/objects >obj-dir-after &&
+	cat >expect <<-\EOF &&
+	info
+	pack
+	EOF
+	test_cmp expect obj-dir-after &&
+	ls .git/objects/pack/*.pack >packs-after &&
+	test_cmp packs-between packs-after
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 4/9] maintenance: create auto condition for loose-objects
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                     ` (2 preceding siblings ...)
  2020-08-18 14:25   ` [PATCH v2 3/9] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
@ 2020-08-18 14:25   ` Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 5/9] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
                     ` (5 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The loose-objects task deletes loose objects that already exist in a
pack-file, then place the remaining loose objects into a new pack-file.
If this step runs all the time, then we risk creating pack-files with
very few objects with every 'git commit' process. To prevent
overwhelming the packs directory with small pack-files, place a minimum
number of objects to justify the task.

The 'maintenance.loose-objects.auto' config option specifies a minimum
number of loose objects to justify the task to run under the '--auto'
option. This defaults to 100 loose objects. Setting the value to zero
will prevent the step from running under '--auto' while a negative value
will force it to run every time.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/maintenance.txt |  9 +++++++++
 builtin/gc.c                         | 30 ++++++++++++++++++++++++++++
 t/t7900-maintenance.sh               | 25 +++++++++++++++++++++++
 3 files changed, 64 insertions(+)

diff --git a/Documentation/config/maintenance.txt b/Documentation/config/maintenance.txt
index 9bd69b9df3..a9442dd260 100644
--- a/Documentation/config/maintenance.txt
+++ b/Documentation/config/maintenance.txt
@@ -12,3 +12,12 @@ maintenance.commit-graph.auto::
 	reachable commits that are not in the commit-graph file is at least
 	the value of `maintenance.commit-graph.auto`. The default value is
 	100.
+
+maintenance.loose-objects.auto::
+	This integer config option controls how often the `loose-objects` task
+	should be run as part of `git maintenance run --auto`. If zero, then
+	the `loose-objects` task will not run with the `--auto` option. A
+	negative value will force the task to run every time. Otherwise, a
+	positive value implies the command should run when the number of
+	loose objects is at least the value of `maintenance.loose-objects.auto`.
+	The default value is 100.
diff --git a/builtin/gc.c b/builtin/gc.c
index 39ea590b5a..61d5752af5 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -926,6 +926,35 @@ struct write_loose_object_data {
 	int batch_size;
 };
 
+static int loose_object_auto_limit = 100;
+
+static int loose_object_count(const struct object_id *oid,
+			       const char *path,
+			       void *data)
+{
+	int *count = (int*)data;
+	if (++(*count) >= loose_object_auto_limit)
+		return 1;
+	return 0;
+}
+
+static int loose_object_auto_condition(void)
+{
+	int count = 0;
+
+	git_config_get_int("maintenance.loose-objects.auto",
+			   &loose_object_auto_limit);
+
+	if (!loose_object_auto_limit)
+		return 0;
+	if (loose_object_auto_limit < 0)
+		return 1;
+
+	return for_each_loose_file_in_objdir(the_repository->objects->odb->path,
+					     loose_object_count,
+					     NULL, NULL, &count);
+}
+
 static int bail_on_loose(const struct object_id *oid,
 			 const char *path,
 			 void *data)
@@ -1035,6 +1064,7 @@ static struct maintenance_task tasks[] = {
 	[TASK_LOOSE_OBJECTS] = {
 		"loose-objects",
 		maintenance_task_loose_objects,
+		loose_object_auto_condition,
 	},
 	[TASK_GC] = {
 		"gc",
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 2e9e369786..efda1cf69b 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -125,4 +125,29 @@ test_expect_success 'loose-objects task' '
 	test_cmp packs-between packs-after
 '
 
+test_expect_success 'maintenance.loose-objects.auto' '
+	git repack -adk &&
+	GIT_TRACE2_EVENT="$(pwd)/trace-lo1.txt" \
+		git -c maintenance.loose-objects.auto=1 maintenance \
+		run --auto --task=loose-objects 2>/dev/null &&
+	test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
+	for i in 1 2
+	do
+		printf data-A-$i | git hash-object -t blob --stdin -w &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-loA-$i" \
+			git -c maintenance.loose-objects.auto=2 \
+			maintenance run --auto --task=loose-objects 2>/dev/null &&
+		test_subcommand ! git prune-packed --quiet <trace-loA-$i &&
+		printf data-B-$i | git hash-object -t blob --stdin -w &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-loB-$i" \
+			git -c maintenance.loose-objects.auto=2 \
+			maintenance run --auto --task=loose-objects 2>/dev/null &&
+		test_subcommand git prune-packed --quiet <trace-loB-$i &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-loC-$i" \
+			git -c maintenance.loose-objects.auto=2 \
+			maintenance run --auto --task=loose-objects 2>/dev/null &&
+		test_subcommand git prune-packed --quiet <trace-loC-$i || return 1
+	done
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 5/9] midx: enable core.multiPackIndex by default
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                     ` (3 preceding siblings ...)
  2020-08-18 14:25   ` [PATCH v2 4/9] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
@ 2020-08-18 14:25   ` Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 6/9] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
                     ` (4 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The core.multiPackIndex setting has been around since c4d25228ebb
(config: create core.multiPackIndex setting, 2018-07-12), but has been
disabled by default. If a user wishes to use the multi-pack-index
feature, then they must enable this config and run 'git multi-pack-index
write'.

The multi-pack-index feature is relatively stable now, so make the
config option true by default. For users that do not use a
multi-pack-index, the only extra cost will be a file lookup to see if a
multi-pack-index file exists (once per process, per object directory).

Also, this config option will be referenced by an upcoming
"incremental-repack" task in the maintenance builtin, so move the config
option into the repository settings struct. Note that if
GIT_TEST_MULTI_PACK_INDEX=1, then we want to ignore the config option
and treat core.multiPackIndex as enabled.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/core.txt |  4 ++--
 midx.c                        | 11 +++--------
 repo-settings.c               |  6 ++++++
 repository.h                  |  2 ++
 4 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 74619a9c03..86c91d5381 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -606,8 +606,8 @@ core.useReplaceRefs::
 
 core.multiPackIndex::
 	Use the multi-pack-index file to track multiple packfiles using a
-	single index. See link:technical/multi-pack-index.html[the
-	multi-pack-index design document].
+	single index. See linkgit:git-multi-pack-index[1] for more
+	information. Defaults to true.
 
 core.sparseCheckout::
 	Enable "sparse checkout" feature. See linkgit:git-sparse-checkout[1]
diff --git a/midx.c b/midx.c
index a5fb797ede..ef499cf504 100644
--- a/midx.c
+++ b/midx.c
@@ -10,6 +10,7 @@
 #include "progress.h"
 #include "trace2.h"
 #include "run-command.h"
+#include "repository.h"
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
@@ -384,15 +385,9 @@ int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, i
 {
 	struct multi_pack_index *m;
 	struct multi_pack_index *m_search;
-	int config_value;
-	static int env_value = -1;
 
-	if (env_value < 0)
-		env_value = git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0);
-
-	if (!env_value &&
-	    (repo_config_get_bool(r, "core.multipackindex", &config_value) ||
-	    !config_value))
+	prepare_repo_settings(r);
+	if (!r->settings.core_multi_pack_index)
 		return 0;
 
 	for (m_search = r->objects->multi_pack_index; m_search; m_search = m_search->next)
diff --git a/repo-settings.c b/repo-settings.c
index 0918408b34..5bd2c22726 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -1,6 +1,7 @@
 #include "cache.h"
 #include "config.h"
 #include "repository.h"
+#include "midx.h"
 
 #define UPDATE_DEFAULT_BOOL(s,v) do { if (s == -1) { s = v; } } while(0)
 
@@ -47,6 +48,11 @@ void prepare_repo_settings(struct repository *r)
 		r->settings.pack_use_sparse = value;
 	UPDATE_DEFAULT_BOOL(r->settings.pack_use_sparse, 1);
 
+	value = git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0);
+	if (value || !repo_config_get_bool(r, "core.multipackindex", &value))
+		r->settings.core_multi_pack_index = value;
+	UPDATE_DEFAULT_BOOL(r->settings.core_multi_pack_index, 1);
+
 	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
 		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
diff --git a/repository.h b/repository.h
index 3c1f7d54bd..3901ce0b65 100644
--- a/repository.h
+++ b/repository.h
@@ -37,6 +37,8 @@ struct repo_settings {
 
 	int pack_use_sparse;
 	enum fetch_negotiation_setting fetch_negotiation_algorithm;
+
+	int core_multi_pack_index;
 };
 
 struct repository {
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 6/9] midx: use start_delayed_progress()
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                     ` (4 preceding siblings ...)
  2020-08-18 14:25   ` [PATCH v2 5/9] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
@ 2020-08-18 14:25   ` Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 7/9] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
                     ` (3 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

Now that the multi-pack-index may be written as part of auto maintenance
at the end of a command, reduce the progress output when the operations
are quick. Use start_delayed_progress() instead of start_progress().

Update t5319-multi-pack-index.sh to use GIT_PROGRESS_DELAY=0 now that
the progress indicators are conditional.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 midx.c                      | 10 +++++-----
 t/t5319-multi-pack-index.sh | 14 +++++++-------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/midx.c b/midx.c
index ef499cf504..aa37d5da86 100644
--- a/midx.c
+++ b/midx.c
@@ -832,7 +832,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 
 	packs.pack_paths_checked = 0;
 	if (flags & MIDX_PROGRESS)
-		packs.progress = start_progress(_("Adding packfiles to multi-pack-index"), 0);
+		packs.progress = start_delayed_progress(_("Adding packfiles to multi-pack-index"), 0);
 	else
 		packs.progress = NULL;
 
@@ -969,7 +969,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 	}
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Writing chunks to multi-pack-index"),
+		progress = start_delayed_progress(_("Writing chunks to multi-pack-index"),
 					  num_chunks);
 	for (i = 0; i < num_chunks; i++) {
 		if (written != chunk_offsets[i])
@@ -1104,7 +1104,7 @@ int verify_midx_file(struct repository *r, const char *object_dir, unsigned flag
 		return 0;
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Looking for referenced packfiles"),
+		progress = start_delayed_progress(_("Looking for referenced packfiles"),
 					  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
 		if (prepare_midx_pack(r, m, i))
@@ -1225,7 +1225,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 	count = xcalloc(m->num_packs, sizeof(uint32_t));
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Counting referenced objects"),
+		progress = start_delayed_progress(_("Counting referenced objects"),
 					  m->num_objects);
 	for (i = 0; i < m->num_objects; i++) {
 		int pack_int_id = nth_midxed_pack_int_id(m, i);
@@ -1235,7 +1235,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 	stop_progress(&progress);
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Finding and deleting unreferenced packfiles"),
+		progress = start_delayed_progress(_("Finding and deleting unreferenced packfiles"),
 					  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
 		char *pack_name;
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 7214cab36c..12f41dfc18 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -172,12 +172,12 @@ test_expect_success 'write progress off for redirected stderr' '
 '
 
 test_expect_success 'write force progress on for stderr' '
-	git multi-pack-index --object-dir=$objdir --progress write 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --progress write 2>err &&
 	test_file_not_empty err
 '
 
 test_expect_success 'write with the --no-progress option' '
-	git multi-pack-index --object-dir=$objdir --no-progress write 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --no-progress write 2>err &&
 	test_line_count = 0 err
 '
 
@@ -334,17 +334,17 @@ test_expect_success 'git-fsck incorrect offset' '
 '
 
 test_expect_success 'repack progress off for redirected stderr' '
-	git multi-pack-index --object-dir=$objdir repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir repack 2>err &&
 	test_line_count = 0 err
 '
 
 test_expect_success 'repack force progress on for stderr' '
-	git multi-pack-index --object-dir=$objdir --progress repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --progress repack 2>err &&
 	test_file_not_empty err
 '
 
 test_expect_success 'repack with the --no-progress option' '
-	git multi-pack-index --object-dir=$objdir --no-progress repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --no-progress repack 2>err &&
 	test_line_count = 0 err
 '
 
@@ -488,7 +488,7 @@ test_expect_success 'expire progress off for redirected stderr' '
 test_expect_success 'expire force progress on for stderr' '
 	(
 		cd dup &&
-		git multi-pack-index --progress expire 2>err &&
+		GIT_PROGRESS_DELAY=0 git multi-pack-index --progress expire 2>err &&
 		test_file_not_empty err
 	)
 '
@@ -496,7 +496,7 @@ test_expect_success 'expire force progress on for stderr' '
 test_expect_success 'expire with the --no-progress option' '
 	(
 		cd dup &&
-		git multi-pack-index --no-progress expire 2>err &&
+		GIT_PROGRESS_DELAY=0 git multi-pack-index --no-progress expire 2>err &&
 		test_line_count = 0 err
 	)
 '
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 7/9] maintenance: add incremental-repack task
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                     ` (5 preceding siblings ...)
  2020-08-18 14:25   ` [PATCH v2 6/9] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
@ 2020-08-18 14:25   ` Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 8/9] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
                     ` (2 subsequent siblings)
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The previous change cleaned up loose objects using the
'loose-objects' that can be run safely in the background. Add a
similar job that performs similar cleanups for pack-files.

One issue with running 'git repack' is that it is designed to
repack all pack-files into a single pack-file. While this is the
most space-efficient way to store object data, it is not time or
memory efficient. This becomes extremely important if the repo is
so large that a user struggles to store two copies of the pack on
their disk.

Instead, perform an "incremental" repack by collecting a few small
pack-files into a new pack-file. The multi-pack-index facilitates
this process ever since 'git multi-pack-index expire' was added in
19575c7 (multi-pack-index: implement 'expire' subcommand,
2019-06-10) and 'git multi-pack-index repack' was added in ce1e4a1
(midx: implement midx_repack(), 2019-06-10).

The 'incremental-repack' task runs the following steps:

1. 'git multi-pack-index write' creates a multi-pack-index file if
   one did not exist, and otherwise will update the multi-pack-index
   with any new pack-files that appeared since the last write. This
   is particularly relevant with the background fetch job.

   When the multi-pack-index sees two copies of the same object, it
   stores the offset data into the newer pack-file. This means that
   some old pack-files could become "unreferenced" which I will use
   to mean "a pack-file that is in the pack-file list of the
   multi-pack-index but none of the objects in the multi-pack-index
   reference a location inside that pack-file."

2. 'git multi-pack-index expire' deletes any unreferenced pack-files
   and updaes the multi-pack-index to drop those pack-files from the
   list. This is safe to do as concurrent Git processes will see the
   multi-pack-index and not open those packs when looking for object
   contents. (Similar to the 'loose-objects' job, there are some Git
   commands that open pack-files regardless of the multi-pack-index,
   but they are rarely used. Further, a user that self-selects to
   use background operations would likely refrain from using those
   commands.)

3. 'git multi-pack-index repack --bacth-size=<size>' collects a set
   of pack-files that are listed in the multi-pack-index and creates
   a new pack-file containing the objects whose offsets are listed
   by the multi-pack-index to be in those objects. The set of pack-
   files is selected greedily by sorting the pack-files by modified
   time and adding a pack-file to the set if its "expected size" is
   smaller than the batch size until the total expected size of the
   selected pack-files is at least the batch size. The "expected
   size" is calculated by taking the size of the pack-file divided
   by the number of objects in the pack-file and multiplied by the
   number of objects from the multi-pack-index with offset in that
   pack-file. The expected size approximates how much data from that
   pack-file will contribute to the resulting pack-file size. The
   intention is that the resulting pack-file will be close in size
   to the provided batch size.

   The next run of the incremental-repack task will delete these
   repacked pack-files during the 'expire' step.

   In this version, the batch size is set to "0" which ignores the
   size restrictions when selecting the pack-files. It instead
   selects all pack-files and repacks all packed objects into a
   single pack-file. This will be updated in the next change, but
   it requires doing some calculations that are better isolated to
   a separate change.

Each of the above steps update the multi-pack-index file. After
each step, we verify the new multi-pack-index. If the new
multi-pack-index is corrupt, then delete the multi-pack-index,
rewrite it from scratch, and stop doing the later steps of the
job. This is intended to be an extra-safe check without leaving
a repo with many pack-files without a multi-pack-index.

These steps are based on a similar background maintenance step in
Scalar (and VFS for Git) [1]. This was incredibly effective for
users of the Windows OS repository. After using the same VFS for Git
repository for over a year, some users had _thousands_ of pack-files
that combined to up to 250 GB of data. We noticed a few users were
running into the open file descriptor limits (due in part to a bug
in the multi-pack-index fixed by af96fe3 (midx: add packs to
packed_git linked list, 2019-04-29).

These pack-files were mostly small since they contained the commits
and trees that were pushed to the origin in a given hour. The GVFS
protocol includes a "prefetch" step that asks for pre-computed pack-
files containing commits and trees by timestamp. These pack-files
were grouped into "daily" pack-files once a day for up to 30 days.
If a user did not request prefetch packs for over 30 days, then they
would get the entire history of commits and trees in a new, large
pack-file. This led to a large number of pack-files that had poor
delta compression.

By running this pack-file maintenance step once per day, these repos
with thousands of packs spanning 200+ GB dropped to dozens of pack-
files spanning 30-50 GB. This was done all without removing objects
from the system and using a constant batch size of two gigabytes.
Once the work was done to reduce the pack-files to small sizes, the
batch size of two gigabytes means that not every run triggers a
repack operation, so the following run will not expire a pack-file.
This has kept these repos in a "clean" state.

[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/PackfileMaintenanceStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt |  15 ++++
 builtin/gc.c                      | 113 ++++++++++++++++++++++++++++++
 midx.c                            |   2 +-
 midx.h                            |   1 +
 t/t5319-multi-pack-index.sh       |   1 +
 t/t7900-maintenance.sh            |  38 ++++++++++
 6 files changed, 169 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 85205b5bb9..b0b73b7185 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -88,6 +88,21 @@ loose-objects::
 	advisable to enable both the `loose-objects` and `gc` tasks at the
 	same time.
 
+incremental-repack::
+	The `incremental-repack` job repacks the object directory
+	using the `multi-pack-index` feature. In order to prevent race
+	conditions with concurrent Git commands, it follows a two-step
+	process. First, it deletes any pack-files included in the
+	`multi-pack-index` where none of the objects in the
+	`multi-pack-index` reference those pack-files; this only happens
+	if all objects in the pack-file are also stored in a newer
+	pack-file. Second, it selects a group of pack-files whose "expected
+	size" is below the batch size until the group has total expected
+	size at least the batch size; see the `--batch-size` option for
+	the `repack` subcommand in linkgit:git-multi-pack-index[1]. The
+	default batch-size is zero, which is a special case that attempts
+	to repack all pack-files into a single pack-file.
+
 OPTIONS
 -------
 --auto::
diff --git a/builtin/gc.c b/builtin/gc.c
index 61d5752af5..9aabef44a8 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -30,6 +30,7 @@
 #include "promisor-remote.h"
 #include "refs.h"
 #include "remote.h"
+#include "midx.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -1028,6 +1029,113 @@ static int maintenance_task_loose_objects(struct maintenance_opts *opts)
 	return prune_packed(opts) || pack_loose(opts);
 }
 
+static int multi_pack_index_write(struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "write", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	if (run_command(&child))
+		return error(_("failed to write multi-pack-index"));
+
+	return 0;
+}
+
+static int rewrite_multi_pack_index(struct maintenance_opts *opts)
+{
+	struct repository *r = the_repository;
+	char *midx_name = get_midx_filename(r->objects->odb->path);
+
+	unlink(midx_name);
+	free(midx_name);
+
+	return multi_pack_index_write(opts);
+}
+
+static int multi_pack_index_verify(struct maintenance_opts *opts,
+				   const char *message)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "verify", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	if (run_command(&child)) {
+		warning(_("'git multi-pack-index verify' failed %s"), message);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int multi_pack_index_expire(struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "expire", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	close_object_store(the_repository->objects);
+
+	if (run_command(&child))
+		return error(_("'git multi-pack-index expire' failed"));
+
+	return 0;
+}
+
+static int multi_pack_index_repack(struct maintenance_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "repack", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	strvec_push(&child.args, "--batch-size=0");
+
+	close_object_store(the_repository->objects);
+
+	if (run_command(&child))
+		return error(_("'git multi-pack-index repack' failed"));
+
+	return 0;
+}
+
+static int maintenance_task_incremental_repack(struct maintenance_opts *opts)
+{
+	prepare_repo_settings(the_repository);
+	if (!the_repository->settings.core_multi_pack_index) {
+		warning(_("skipping incremental-repack task because core.multiPackIndex is disabled"));
+		return 0;
+	}
+
+	if (multi_pack_index_write(opts))
+		return 1;
+	if (multi_pack_index_verify(opts, "after initial write"))
+		return rewrite_multi_pack_index(opts);
+	if (multi_pack_index_expire(opts))
+		return 1;
+	if (multi_pack_index_verify(opts, "after expire step"))
+		return !!rewrite_multi_pack_index(opts);
+	if (multi_pack_index_repack(opts))
+		return 1;
+	if (multi_pack_index_verify(opts, "after repack step"))
+		return !!rewrite_multi_pack_index(opts);
+	return 0;
+}
+
 typedef int maintenance_task_fn(struct maintenance_opts *opts);
 
 /*
@@ -1049,6 +1157,7 @@ struct maintenance_task {
 enum maintenance_task_label {
 	TASK_PREFETCH,
 	TASK_LOOSE_OBJECTS,
+	TASK_INCREMENTAL_REPACK,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -1066,6 +1175,10 @@ static struct maintenance_task tasks[] = {
 		maintenance_task_loose_objects,
 		loose_object_auto_condition,
 	},
+	[TASK_INCREMENTAL_REPACK] = {
+		"incremental-repack",
+		maintenance_task_incremental_repack,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/midx.c b/midx.c
index aa37d5da86..66d7053d83 100644
--- a/midx.c
+++ b/midx.c
@@ -37,7 +37,7 @@
 
 #define PACK_EXPIRED UINT_MAX
 
-static char *get_midx_filename(const char *object_dir)
+char *get_midx_filename(const char *object_dir)
 {
 	return xstrfmt("%s/pack/multi-pack-index", object_dir);
 }
diff --git a/midx.h b/midx.h
index b18cf53bc4..baeecc70c9 100644
--- a/midx.h
+++ b/midx.h
@@ -37,6 +37,7 @@ struct multi_pack_index {
 
 #define MIDX_PROGRESS     (1 << 0)
 
+char *get_midx_filename(const char *object_dir);
 struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local);
 int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
 int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result);
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 12f41dfc18..26f224b0e3 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -3,6 +3,7 @@
 test_description='multi-pack-indexes'
 . ./test-lib.sh
 
+GIT_TEST_MULTI_PACK_INDEX=0
 objdir=.git/objects
 
 midx_read_expect () {
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index efda1cf69b..dde28cf837 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -5,6 +5,7 @@ test_description='git maintenance builtin'
 . ./test-lib.sh
 
 GIT_TEST_COMMIT_GRAPH=0
+GIT_TEST_MULTI_PACK_INDEX=0
 
 test_expect_success 'help text' '
 	test_expect_code 129 git maintenance -h 2>err &&
@@ -150,4 +151,41 @@ test_expect_success 'maintenance.loose-objects.auto' '
 	done
 '
 
+test_expect_success 'incremental-repack task' '
+	packDir=.git/objects/pack &&
+	for i in $(test_seq 1 5)
+	do
+		test_commit $i || return 1
+	done &&
+
+	# Create three disjoint pack-files with size BIG, small, small.
+	echo HEAD~2 | git pack-objects --revs $packDir/test-1 &&
+	test_tick &&
+	git pack-objects --revs $packDir/test-2 <<-\EOF &&
+	HEAD~1
+	^HEAD~2
+	EOF
+	test_tick &&
+	git pack-objects --revs $packDir/test-3 <<-\EOF &&
+	HEAD
+	^HEAD~1
+	EOF
+	rm -f $packDir/pack-* &&
+	rm -f $packDir/loose-* &&
+	ls $packDir/*.pack >packs-before &&
+	test_line_count = 3 packs-before &&
+
+	# the job repacks the two into a new pack, but does not
+	# delete the old ones.
+	git maintenance run --task=incremental-repack &&
+	ls $packDir/*.pack >packs-between &&
+	test_line_count = 4 packs-between &&
+
+	# the job deletes the two old packs, and does not write
+	# a new one because only one pack remains.
+	git maintenance run --task=incremental-repack &&
+	ls .git/objects/pack/*.pack >packs-after &&
+	test_line_count = 1 packs-after
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 8/9] maintenance: auto-size incremental-repack batch
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                     ` (6 preceding siblings ...)
  2020-08-18 14:25   ` [PATCH v2 7/9] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
@ 2020-08-18 14:25   ` Derrick Stolee via GitGitGadget
  2020-08-18 14:25   ` [PATCH v2 9/9] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

When repacking during the 'incremental-repack' task, we use the
--batch-size option in 'git multi-pack-index repack'. The initial setting
used --batch-size=0 to repack everything into a single pack-file. This is
not sustainable for a large repository. The amount of work required is
also likely to use too many system resources for a background job.

Update the 'incremental-repack' task by dynamically computing a
--batch-size option based on the current pack-file structure.

The dynamic default size is computed with this idea in mind for a client
repository that was cloned from a very large remote: there is likely one
"big" pack-file that was created at clone time. Thus, do not try
repacking it as it is likely packed efficiently by the server.

Instead, we select the second-largest pack-file, and create a batch size
that is one larger than that pack-file. If there are three or more
pack-files, then this guarantees that at least two will be combined into
a new pack-file.

Of course, this means that the second-largest pack-file size is likely
to grow over time and may eventually surpass the initially-cloned
pack-file. Recall that the pack-file batch is selected in a greedy
manner: the packs are considered from oldest to newest and are selected
if they have size smaller than the batch size until the total selected
size is larger than the batch size. Thus, that oldest "clone" pack will
be first to repack after the new data creates a pack larger than that.

We also want to place some limits on how large these pack-files become,
in order to bound the amount of time spent repacking. A maximum
batch-size of two gigabytes means that large repositories will never be
packed into a single pack-file using this job, but also that repack is
rather expensive. This is a trade-off that is valuable to have if the
maintenance is being run automatically or in the background. Users who
truly want to optimize for space and performance (and are willing to pay
the upfront cost of a full repack) can use the 'gc' task to do so.

Create a test for this two gigabyte limit by creating an EXPENSIVE test
that generates two pack-files of roughly 2.5 gigabytes in size, then
performs an incremental repack. Check that the --batch-size argument in
the subcommand uses the hard-coded maximum.

Helped-by: Chris Torek <chris.torek@gmail.com>
Reported-by: Son Luong Ngoc <sluongng@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 builtin/gc.c           | 43 +++++++++++++++++++++++++++++++++++++++++-
 t/t7900-maintenance.sh | 36 +++++++++++++++++++++++++++++++++--
 2 files changed, 76 insertions(+), 3 deletions(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 9aabef44a8..d2f3e27e54 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1093,6 +1093,46 @@ static int multi_pack_index_expire(struct maintenance_opts *opts)
 	return 0;
 }
 
+#define TWO_GIGABYTES (INT32_MAX)
+
+static off_t get_auto_pack_size(void)
+{
+	/*
+	 * The "auto" value is special: we optimize for
+	 * one large pack-file (i.e. from a clone) and
+	 * expect the rest to be small and they can be
+	 * repacked quickly.
+	 *
+	 * The strategy we select here is to select a
+	 * size that is one more than the second largest
+	 * pack-file. This ensures that we will repack
+	 * at least two packs if there are three or more
+	 * packs.
+	 */
+	off_t max_size = 0;
+	off_t second_largest_size = 0;
+	off_t result_size;
+	struct packed_git *p;
+	struct repository *r = the_repository;
+
+	reprepare_packed_git(r);
+	for (p = get_all_packs(r); p; p = p->next) {
+		if (p->pack_size > max_size) {
+			second_largest_size = max_size;
+			max_size = p->pack_size;
+		} else if (p->pack_size > second_largest_size)
+			second_largest_size = p->pack_size;
+	}
+
+	result_size = second_largest_size + 1;
+
+	/* But limit ourselves to a batch size of 2g */
+	if (result_size > TWO_GIGABYTES)
+		result_size = TWO_GIGABYTES;
+
+	return result_size;
+}
+
 static int multi_pack_index_repack(struct maintenance_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -1103,7 +1143,8 @@ static int multi_pack_index_repack(struct maintenance_opts *opts)
 	if (opts->quiet)
 		strvec_push(&child.args, "--no-progress");
 
-	strvec_push(&child.args, "--batch-size=0");
+	strvec_pushf(&child.args, "--batch-size=%"PRIuMAX,
+				  (uintmax_t)get_auto_pack_size());
 
 	close_object_store(the_repository->objects);
 
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index dde28cf837..5c08afc19a 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -182,10 +182,42 @@ test_expect_success 'incremental-repack task' '
 	test_line_count = 4 packs-between &&
 
 	# the job deletes the two old packs, and does not write
-	# a new one because only one pack remains.
+	# a new one because the batch size is not high enough to
+	# pack the largest pack-file.
 	git maintenance run --task=incremental-repack &&
 	ls .git/objects/pack/*.pack >packs-after &&
-	test_line_count = 1 packs-after
+	test_line_count = 2 packs-after
+'
+
+test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
+	for i in $(test_seq 1 5)
+	do
+		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
+		return 1
+	done &&
+	git add big &&
+	git commit -m "Add big file (1)" &&
+
+	# ensure any possible loose objects are in a pack-file
+	git maintenance run --task=loose-objects &&
+
+	rm big &&
+	for i in $(test_seq 6 10)
+	do
+		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
+		return 1
+	done &&
+	git add big &&
+	git commit -m "Add big file (2)" &&
+
+	# ensure any possible loose objects are in a pack-file
+	git maintenance run --task=loose-objects &&
+
+	# Now run the incremental-repack task and check the batch-size
+	GIT_TRACE2_EVENT="$(pwd)/run-2g.txt" git maintenance run \
+		--task=incremental-repack 2>/dev/null &&
+	test_subcommand git multi-pack-index repack \
+		 --no-progress --batch-size=2147483647 <run-2g.txt
 '
 
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v2 9/9] maintenance: add incremental-repack auto condition
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                     ` (7 preceding siblings ...)
  2020-08-18 14:25   ` [PATCH v2 8/9] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
@ 2020-08-18 14:25   ` Derrick Stolee via GitGitGadget
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  9 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-18 14:25 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The incremental-repack task updates the multi-pack-index by deleting pack-
files that have been replaced with new packs, then repacking a batch of
small pack-files into a larger pack-file. This incremental repack is faster
than rewriting all object data, but is slower than some other
maintenance activities.

The 'maintenance.incremental-repack.auto' config option specifies how many
pack-files should exist outside of the multi-pack-index before running
the step. These pack-files could be created by 'git fetch' commands or
by the loose-objects task. The default value is 10.

Setting the option to zero disables the task with the '--auto' option,
and a negative value makes the task run every time.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/maintenance.txt |  9 ++++++++
 builtin/gc.c                         | 31 ++++++++++++++++++++++++++++
 t/t7900-maintenance.sh               | 31 ++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+)

diff --git a/Documentation/config/maintenance.txt b/Documentation/config/maintenance.txt
index a9442dd260..22229e7174 100644
--- a/Documentation/config/maintenance.txt
+++ b/Documentation/config/maintenance.txt
@@ -21,3 +21,12 @@ maintenance.loose-objects.auto::
 	positive value implies the command should run when the number of
 	loose objects is at least the value of `maintenance.loose-objects.auto`.
 	The default value is 100.
+
+maintenance.incremental-repack.auto::
+	This integer config option controls how often the `incremental-repack`
+	task should be run as part of `git maintenance run --auto`. If zero,
+	then the `incremental-repack` task will not run with the `--auto`
+	option. A negative value will force the task to run every time.
+	Otherwise, a positive value implies the command should run when the
+	number of pack-files not in the multi-pack-index is at least the value
+	of `maintenance.incremental-repack.auto`. The default value is 10.
diff --git a/builtin/gc.c b/builtin/gc.c
index d2f3e27e54..7fa0e2fe97 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -31,6 +31,7 @@
 #include "refs.h"
 #include "remote.h"
 #include "midx.h"
+#include "object-store.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -1029,6 +1030,35 @@ static int maintenance_task_loose_objects(struct maintenance_opts *opts)
 	return prune_packed(opts) || pack_loose(opts);
 }
 
+static int incremental_repack_auto_condition(void)
+{
+	struct packed_git *p;
+	int enabled;
+	int incremental_repack_auto_limit = 10;
+	int count = 0;
+
+	if (git_config_get_bool("core.multiPackIndex", &enabled) ||
+	    !enabled)
+		return 0;
+
+	git_config_get_int("maintenance.incremental-repack.auto",
+			   &incremental_repack_auto_limit);
+
+	if (!incremental_repack_auto_limit)
+		return 0;
+	if (incremental_repack_auto_limit < 0)
+		return 1;
+
+	for (p = get_packed_git(the_repository);
+	     count < incremental_repack_auto_limit && p;
+	     p = p->next) {
+		if (!p->multi_pack_index)
+			count++;
+	}
+
+	return count >= incremental_repack_auto_limit;
+}
+
 static int multi_pack_index_write(struct maintenance_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -1219,6 +1249,7 @@ static struct maintenance_task tasks[] = {
 	[TASK_INCREMENTAL_REPACK] = {
 		"incremental-repack",
 		maintenance_task_incremental_repack,
+		incremental_repack_auto_condition,
 	},
 	[TASK_GC] = {
 		"gc",
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 5c08afc19a..6f878b0141 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -220,4 +220,35 @@ test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
 		 --no-progress --batch-size=2147483647 <run-2g.txt
 '
 
+test_expect_success 'maintenance.incremental-repack.auto' '
+	git repack -adk &&
+	git config core.multiPackIndex true &&
+	git multi-pack-index write &&
+	GIT_TRACE2_EVENT="$(pwd)/midx-init.txt" git \
+		-c maintenance.incremental-repack.auto=1 \
+		maintenance run --auto --task=incremental-repack 2>/dev/null &&
+	test_subcommand ! git multi-pack-index write --no-progress <midx-init.txt &&
+	for i in 1 2
+	do
+		test_commit A-$i &&
+		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
+		HEAD
+		^HEAD~1
+		EOF
+		GIT_TRACE2_EVENT=$(pwd)/trace-A-$i git \
+			-c maintenance.incremental-repack.auto=2 \
+			maintenance run --auto --task=incremental-repack 2>/dev/null &&
+		test_subcommand ! git multi-pack-index write --no-progress <trace-A-$i &&
+		test_commit B-$i &&
+		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
+		HEAD
+		^HEAD~1
+		EOF
+		GIT_TRACE2_EVENT=$(pwd)/trace-B-$i git \
+			-c maintenance.incremental-repack.auto=2 \
+			maintenance run --auto --task=incremental-repack 2>/dev/null &&
+		test_subcommand git multi-pack-index write --no-progress <trace-B-$i || return 1
+	done
+'
+
 test_done
-- 
gitgitgadget

^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks
  2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                     ` (8 preceding siblings ...)
  2020-08-18 14:25   ` [PATCH v2 9/9] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
@ 2020-08-25 18:36   ` Derrick Stolee via GitGitGadget
  2020-08-25 18:36     ` [PATCH v3 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
                       ` (10 more replies)
  9 siblings, 11 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-25 18:36 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee

This series is based on v3 of part I (ds/maintenance-part-1) [2].

This patch series contains 9 patches that were going to be part of v4 of
ds/maintenance [1], but the discussion has gotten really long. To help, I'm
splitting out the portions that create and test the 'maintenance' builtin
from the additional tasks (prefetch, loose-objects, incremental-repack) that
can be brought in later.

[1] 
https://lore.kernel.org/git/pull.671.git.1594131695.gitgitgadget@gmail.com/
[2] 
https://lore.kernel.org/git/pull.695.v3.git.1598380426.gitgitgadget@gmail.com/

As detailed in [2], the 'git maintenance run' subcommand will run certain
tasks based on config options or the --task= arguments. The --auto option
indicates to the task to only run based on some internal check that there
has been "enough" change in that domain to merit the work. In the case of
the 'gc' task, this also reduces the amount of work done. 

The new maintenance tasks in this series are:

 * 'loose-objects' : prune packed loose objects, then create a new pack from
   a batch of loose objects.
 * 'pack-files' : expire redundant packs from the multi-pack-index, then
   repack using the multi-pack-index's incremental repack strategy.
 * 'prefetch' : fetch from each remote, storing the refs in 'refs/prefetch/
   /'.

These tasks are all disabled by default, but can be enabled with config
options or run explicitly using "git maintenance run --task=". 

Since [2] replaced the 'git gc --auto' calls with 'git maintenance run
--auto' at the end of some Git commands, users could replace the 'gc' task
with these lighter-weight changes for foreground maintenance.

The 'git maintenance' builtin has a 'run' subcommand so it can be extended
later with subcommands that manage background maintenance, such as 'start'
or 'stop'. These are not the subject of this series, as it is important to
focus on the maintenance activities themselves. I have an RFC series for
this available at [3].

[3] 
https://lore.kernel.org/git/pull.680.git.1597857408.gitgitgadget@gmail.com/

Updates since v2
================

 * Dropped "fetch: optionally allow disabling FETCH_HEAD update"
   
   
 * A lot of fallout from the change in the option parsing in v3 of
   Maintenance II.
   
   
 * Dropped the "verify, and delete and rewrite on failure" logic from the
   incremental-repack task. This might be added again later after it can be
   tested more thoroughly.
   
   

Updates since v1 (of this series)
=================================

 * PATCH 1 ("fetch: optionally allow disabling FETCH_HEAD update") was
   rewritten on-list. Getting a version out with this patch is the main
   reason for rolling a v2. (That, and Part I is re-rolled with a v2 and I
   want to make sure this series applies cleanly.)
   
   
 * The 'prefetch' and 'loose-objects' tasks had some review, but my proposed
   changes were not acked, so they may need another review.
   
   

UPDATES since v3 of [1]
=======================

 * The biggest change here is the use of "test_subcommand", based on
   Jonathan Nieder's approach. This requires having the exact command-line
   figured out, which now requires spelling out all --no- [quiet%7Cprogress] 
   options. I also added a bunch of "2>/dev/null" checks because of the
   isatty(2) calls. Without that, the behavior will change depending on
   whether the test is run with -x/-v or without.
   
   
 * The 0x7FFF/0x7FFFFFFF constant problem is fixed with an EXPENSIVE test
   that verifies it.
   
   
 * The option parsing has changed to use a local struct and pass that struct
   to the helper methods. This is instead of having a global singleton.
   
   

Thanks, -Stolee

Derrick Stolee (8):
  maintenance: add prefetch task
  maintenance: add loose-objects task
  maintenance: create auto condition for loose-objects
  midx: enable core.multiPackIndex by default
  midx: use start_delayed_progress()
  maintenance: add incremental-repack task
  maintenance: auto-size incremental-repack batch
  maintenance: add incremental-repack auto condition

 Documentation/config/core.txt        |   4 +-
 Documentation/config/maintenance.txt |  18 ++
 Documentation/git-maintenance.txt    |  45 ++++
 builtin/gc.c                         | 327 +++++++++++++++++++++++++++
 midx.c                               |  23 +-
 midx.h                               |   1 +
 repo-settings.c                      |   6 +
 repository.h                         |   2 +
 t/t5319-multi-pack-index.sh          |  15 +-
 t/t7900-maintenance.sh               | 191 ++++++++++++++++
 10 files changed, 609 insertions(+), 23 deletions(-)


base-commit: 652a8eac57d04a51820c7a5b45031b50c5188e7b
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-696%2Fderrickstolee%2Fmaintenance%2Fgc-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-696/derrickstolee/maintenance/gc-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/696

Range-diff vs v2:

  1:  f3bc0b2d92 <  -:  ---------- fetch: optionally allow disabling FETCH_HEAD update
  2:  8779c6c20d !  1:  da64c51a81 maintenance: add prefetch task
     @@ Commit message
          Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
      
       ## Documentation/git-maintenance.txt ##
     -@@ Documentation/git-maintenance.txt: since it will not expire `.graph` files that were in the previous
     - `commit-graph-chain` file. They will be deleted by a later run based on
     - the expiration delay.
     +@@ Documentation/git-maintenance.txt: commit-graph::
     + 	`commit-graph-chain` file. They will be deleted by a later run based
     + 	on the expiration delay.
       
      +prefetch::
      +	The `prefetch` task updates the object directory with the latest
     @@ builtin/gc.c
       
       #define FAILED_RUN "failed to run %s"
       
     -@@ builtin/gc.c: static int maintenance_task_commit_graph(struct maintenance_opts *opts)
     - 	return 1;
     +@@ builtin/gc.c: static int maintenance_task_commit_graph(struct maintenance_run_opts *opts)
     + 	return 0;
       }
       
     -+static int fetch_remote(const char *remote, struct maintenance_opts *opts)
     ++static int fetch_remote(const char *remote, struct maintenance_run_opts *opts)
      +{
      +	struct child_process child = CHILD_PROCESS_INIT;
      +
     @@ builtin/gc.c: static int maintenance_task_commit_graph(struct maintenance_opts *
      +	return 0;
      +}
      +
     -+static int maintenance_task_prefetch(struct maintenance_opts *opts)
     ++static int maintenance_task_prefetch(struct maintenance_run_opts *opts)
      +{
      +	int result = 0;
      +	struct string_list_item *item;
     @@ builtin/gc.c: static int maintenance_task_commit_graph(struct maintenance_opts *
      +	return result;
      +}
      +
     - static int maintenance_task_gc(struct maintenance_opts *opts)
     + static int maintenance_task_gc(struct maintenance_run_opts *opts)
       {
       	struct child_process child = CHILD_PROCESS_INIT;
      @@ builtin/gc.c: struct maintenance_task {
  3:  4fa9d298b9 !  2:  75e846456b maintenance: add loose-objects task
     @@ Documentation/git-maintenance.txt: gc::
       --auto::
      
       ## builtin/gc.c ##
     -@@ builtin/gc.c: static int maintenance_task_gc(struct maintenance_opts *opts)
     +@@ builtin/gc.c: static int maintenance_task_gc(struct maintenance_run_opts *opts)
       	return run_command(&child);
       }
       
     -+static int prune_packed(struct maintenance_opts *opts)
     ++static int prune_packed(struct maintenance_run_opts *opts)
      +{
      +	struct child_process child = CHILD_PROCESS_INIT;
      +
     @@ builtin/gc.c: static int maintenance_task_gc(struct maintenance_opts *opts)
      +	return ++(d->count) > d->batch_size;
      +}
      +
     -+static int pack_loose(struct maintenance_opts *opts)
     ++static int pack_loose(struct maintenance_run_opts *opts)
      +{
      +	struct repository *r = the_repository;
      +	int result = 0;
     @@ builtin/gc.c: static int maintenance_task_gc(struct maintenance_opts *opts)
      +	return result;
      +}
      +
     -+static int maintenance_task_loose_objects(struct maintenance_opts *opts)
     ++static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
      +{
      +	return prune_packed(opts) || pack_loose(opts);
      +}
      +
     - typedef int maintenance_task_fn(struct maintenance_opts *opts);
     + typedef int maintenance_task_fn(struct maintenance_run_opts *opts);
       
       /*
      @@ builtin/gc.c: struct maintenance_task {
  4:  3432bc3167 =  3:  d6e382c43e maintenance: create auto condition for loose-objects
  5:  0ee2434bdb =  4:  d0f2ec70d9 midx: enable core.multiPackIndex by default
  6:  e157ea8dd7 =  5:  2cd3c803d9 midx: use start_delayed_progress()
  7:  a8d956dad6 !  6:  0dd26bb584 maintenance: add incremental-repack task
     @@ Commit message
             it requires doing some calculations that are better isolated to
             a separate change.
      
     -    Each of the above steps update the multi-pack-index file. After
     -    each step, we verify the new multi-pack-index. If the new
     -    multi-pack-index is corrupt, then delete the multi-pack-index,
     -    rewrite it from scratch, and stop doing the later steps of the
     -    job. This is intended to be an extra-safe check without leaving
     -    a repo with many pack-files without a multi-pack-index.
     -
          These steps are based on a similar background maintenance step in
          Scalar (and VFS for Git) [1]. This was incredibly effective for
          users of the Windows OS repository. After using the same VFS for Git
     @@ builtin/gc.c
       
       #define FAILED_RUN "failed to run %s"
       
     -@@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_opts *opts)
     +@@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
       	return prune_packed(opts) || pack_loose(opts);
       }
       
     -+static int multi_pack_index_write(struct maintenance_opts *opts)
     ++static int multi_pack_index_write(struct maintenance_run_opts *opts)
      +{
      +	struct child_process child = CHILD_PROCESS_INIT;
      +
     @@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_opts
      +	return 0;
      +}
      +
     -+static int rewrite_multi_pack_index(struct maintenance_opts *opts)
     -+{
     -+	struct repository *r = the_repository;
     -+	char *midx_name = get_midx_filename(r->objects->odb->path);
     -+
     -+	unlink(midx_name);
     -+	free(midx_name);
     -+
     -+	return multi_pack_index_write(opts);
     -+}
     -+
     -+static int multi_pack_index_verify(struct maintenance_opts *opts,
     -+				   const char *message)
     -+{
     -+	struct child_process child = CHILD_PROCESS_INIT;
     -+
     -+	child.git_cmd = 1;
     -+	strvec_pushl(&child.args, "multi-pack-index", "verify", NULL);
     -+
     -+	if (opts->quiet)
     -+		strvec_push(&child.args, "--no-progress");
     -+
     -+	if (run_command(&child)) {
     -+		warning(_("'git multi-pack-index verify' failed %s"), message);
     -+		return 1;
     -+	}
     -+
     -+	return 0;
     -+}
     -+
     -+static int multi_pack_index_expire(struct maintenance_opts *opts)
     ++static int multi_pack_index_expire(struct maintenance_run_opts *opts)
      +{
      +	struct child_process child = CHILD_PROCESS_INIT;
      +
     @@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_opts
      +	return 0;
      +}
      +
     -+static int multi_pack_index_repack(struct maintenance_opts *opts)
     ++static int multi_pack_index_repack(struct maintenance_run_opts *opts)
      +{
      +	struct child_process child = CHILD_PROCESS_INIT;
      +
     @@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_opts
      +	return 0;
      +}
      +
     -+static int maintenance_task_incremental_repack(struct maintenance_opts *opts)
     ++static int maintenance_task_incremental_repack(struct maintenance_run_opts *opts)
      +{
      +	prepare_repo_settings(the_repository);
      +	if (!the_repository->settings.core_multi_pack_index) {
     @@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_opts
      +
      +	if (multi_pack_index_write(opts))
      +		return 1;
     -+	if (multi_pack_index_verify(opts, "after initial write"))
     -+		return rewrite_multi_pack_index(opts);
      +	if (multi_pack_index_expire(opts))
      +		return 1;
     -+	if (multi_pack_index_verify(opts, "after expire step"))
     -+		return !!rewrite_multi_pack_index(opts);
      +	if (multi_pack_index_repack(opts))
      +		return 1;
     -+	if (multi_pack_index_verify(opts, "after repack step"))
     -+		return !!rewrite_multi_pack_index(opts);
      +	return 0;
      +}
      +
     - typedef int maintenance_task_fn(struct maintenance_opts *opts);
     + typedef int maintenance_task_fn(struct maintenance_run_opts *opts);
       
       /*
      @@ builtin/gc.c: struct maintenance_task {
  8:  f0e7276755 !  7:  f3b25a9927 maintenance: auto-size incremental-repack batch
     @@ Commit message
          Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
      
       ## builtin/gc.c ##
     -@@ builtin/gc.c: static int multi_pack_index_expire(struct maintenance_opts *opts)
     +@@ builtin/gc.c: static int multi_pack_index_expire(struct maintenance_run_opts *opts)
       	return 0;
       }
       
     @@ builtin/gc.c: static int multi_pack_index_expire(struct maintenance_opts *opts)
      +	return result_size;
      +}
      +
     - static int multi_pack_index_repack(struct maintenance_opts *opts)
     + static int multi_pack_index_repack(struct maintenance_run_opts *opts)
       {
       	struct child_process child = CHILD_PROCESS_INIT;
     -@@ builtin/gc.c: static int multi_pack_index_repack(struct maintenance_opts *opts)
     +@@ builtin/gc.c: static int multi_pack_index_repack(struct maintenance_run_opts *opts)
       	if (opts->quiet)
       		strvec_push(&child.args, "--no-progress");
       
  9:  5659a23ad5 !  8:  e9bb32f53a maintenance: add incremental-repack auto condition
     @@ builtin/gc.c
       
       #define FAILED_RUN "failed to run %s"
       
     -@@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_opts *opts)
     +@@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
       	return prune_packed(opts) || pack_loose(opts);
       }
       
     @@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_opts
      +	return count >= incremental_repack_auto_limit;
      +}
      +
     - static int multi_pack_index_write(struct maintenance_opts *opts)
     + static int multi_pack_index_write(struct maintenance_run_opts *opts)
       {
       	struct child_process child = CHILD_PROCESS_INIT;
      @@ builtin/gc.c: static struct maintenance_task tasks[] = {

-- 
gitgitgadget

^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3 1/8] maintenance: add prefetch task
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
@ 2020-08-25 18:36     ` Derrick Stolee via GitGitGadget
  2020-09-22 23:05       ` Jonathan Tan
  2020-08-25 18:36     ` [PATCH v3 2/8] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
                       ` (9 subsequent siblings)
  10 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-25 18:36 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

When working with very large repositories, an incremental 'git fetch'
command can download a large amount of data. If there are many other
users pushing to a common repo, then this data can rival the initial
pack-file size of a 'git clone' of a medium-size repo.

Users may want to keep the data on their local repos as close as
possible to the data on the remote repos by fetching periodically in
the background. This can break up a large daily fetch into several
smaller hourly fetches.

The task is called "prefetch" because it is work done in advance
of a foreground fetch to make that 'git fetch' command much faster.

However, if we simply ran 'git fetch <remote>' in the background,
then the user running a foregroudn 'git fetch <remote>' would lose
some important feedback when a new branch appears or an existing
branch updates. This is especially true if a remote branch is
force-updated and this isn't noticed by the user because it occurred
in the background. Further, the functionality of 'git push
--force-with-lease' becomes suspect.

When running 'git fetch <remote> <options>' in the background, use
the following options for careful updating:

1. --no-tags prevents getting a new tag when a user wants to see
   the new tags appear in their foreground fetches.

2. --refmap= removes the configured refspec which usually updates
   refs/remotes/<remote>/* with the refs advertised by the remote.
   While this looks confusing, this was documented and tested by
   b40a50264ac (fetch: document and test --refmap="", 2020-01-21),
   including this sentence in the documentation:

	Providing an empty `<refspec>` to the `--refmap` option
	causes Git to ignore the configured refspecs and rely
	entirely on the refspecs supplied as command-line arguments.

3. By adding a new refspec "+refs/heads/*:refs/prefetch/<remote>/*"
   we can ensure that we actually load the new values somewhere in
   our refspace while not updating refs/heads or refs/remotes. By
   storing these refs here, the commit-graph job will update the
   commit-graph with the commits from these hidden refs.

4. --prune will delete the refs/prefetch/<remote> refs that no
   longer appear on the remote.

5. --no-write-fetch-head prevents updating FETCH_HEAD.

We've been using this step as a critical background job in Scalar
[1] (and VFS for Git). This solved a pain point that was showing up
in user reports: fetching was a pain! Users do not like waiting to
download the data that was created while they were away from their
machines. After implementing background fetch, the foreground fetch
commands sped up significantly because they mostly just update refs
and download a small amount of new data. The effect is especially
dramatic when paried with --no-show-forced-udpates (through
fetch.showForcedUpdates=false).

[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/FetchStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 15 +++++++++
 builtin/gc.c                      | 51 +++++++++++++++++++++++++++++++
 t/t7900-maintenance.sh            | 26 ++++++++++++++++
 3 files changed, 92 insertions(+)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 6abcb8255a..12668fccf7 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -47,6 +47,21 @@ commit-graph::
 	`commit-graph-chain` file. They will be deleted by a later run based
 	on the expiration delay.
 
+prefetch::
+	The `prefetch` task updates the object directory with the latest
+	objects from all registered remotes. For each remote, a `git fetch`
+	command is run. The refmap is custom to avoid updating local or remote
+	branches (those in `refs/heads` or `refs/remotes`). Instead, the
+	remote refs are stored in `refs/prefetch/<remote>/`. Also, tags are
+	not updated.
++
+This is done to avoid disrupting the remote-tracking branches. The end users
+expect these refs to stay unmoved unless they initiate a fetch.  With prefetch
+task, however, the objects necessary to complete a later real fetch would
+already be obtained, so the real fetch would go faster.  In the ideal case,
+it will just become an update to bunch of remote-tracking branches without
+any object transfer.
+
 gc::
 	Clean up unnecessary files and optimize the local repository. "GC"
 	stands for "garbage collection," but this task performs many
diff --git a/builtin/gc.c b/builtin/gc.c
index c3bcdc1167..eb9c4d6147 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -29,6 +29,7 @@
 #include "tree.h"
 #include "promisor-remote.h"
 #include "refs.h"
+#include "remote.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -816,6 +817,51 @@ static int maintenance_task_commit_graph(struct maintenance_run_opts *opts)
 	return 0;
 }
 
+static int fetch_remote(const char *remote, struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "fetch", remote, "--prune", "--no-tags",
+		     "--no-write-fetch-head", "--recurse-submodules=no",
+		     "--refmap=", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--quiet");
+
+	strvec_pushf(&child.args, "+refs/heads/*:refs/prefetch/%s/*", remote);
+
+	return !!run_command(&child);
+}
+
+static int append_remote(struct remote *remote, void *cbdata)
+{
+	struct string_list *remotes = (struct string_list *)cbdata;
+
+	string_list_append(remotes, remote->name);
+	return 0;
+}
+
+static int maintenance_task_prefetch(struct maintenance_run_opts *opts)
+{
+	int result = 0;
+	struct string_list_item *item;
+	struct string_list remotes = STRING_LIST_INIT_DUP;
+
+	if (for_each_remote(append_remote, &remotes)) {
+		error(_("failed to fill remotes"));
+		result = 1;
+		goto cleanup;
+	}
+
+	for_each_string_list_item(item, &remotes)
+		result |= fetch_remote(item->string, opts);
+
+cleanup:
+	string_list_clear(&remotes, 0);
+	return result;
+}
+
 static int maintenance_task_gc(struct maintenance_run_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -854,6 +900,7 @@ struct maintenance_task {
 };
 
 enum maintenance_task_label {
+	TASK_PREFETCH,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -862,6 +909,10 @@ enum maintenance_task_label {
 };
 
 static struct maintenance_task tasks[] = {
+	[TASK_PREFETCH] = {
+		"prefetch",
+		maintenance_task_prefetch,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 4f6a04ddb1..0bade09c43 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -60,4 +60,30 @@ test_expect_success 'run --task duplicate' '
 	test_i18ngrep "cannot be selected multiple times" err
 '
 
+test_expect_success 'run --task=prefetch with no remotes' '
+	git maintenance run --task=prefetch 2>err &&
+	test_must_be_empty err
+'
+
+test_expect_success 'prefetch multiple remotes' '
+	git clone . clone1 &&
+	git clone . clone2 &&
+	git remote add remote1 "file://$(pwd)/clone1" &&
+	git remote add remote2 "file://$(pwd)/clone2" &&
+	git -C clone1 switch -c one &&
+	git -C clone2 switch -c two &&
+	test_commit -C clone1 one &&
+	test_commit -C clone2 two &&
+	GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null &&
+	fetchargs="--prune --no-tags --no-write-fetch-head --recurse-submodules=no --refmap= --quiet" &&
+	test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\* <run-prefetch.txt &&
+	test_subcommand git fetch remote2 $fetchargs +refs/heads/\\*:refs/prefetch/remote2/\\* <run-prefetch.txt &&
+	test_path_is_missing .git/refs/remotes &&
+	git log prefetch/remote1/one &&
+	git log prefetch/remote2/two &&
+	git fetch --all &&
+	test_cmp_rev refs/remotes/remote1/one refs/prefetch/remote1/one &&
+	test_cmp_rev refs/remotes/remote2/two refs/prefetch/remote2/two
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3 2/8] maintenance: add loose-objects task
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  2020-08-25 18:36     ` [PATCH v3 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
@ 2020-08-25 18:36     ` Derrick Stolee via GitGitGadget
  2020-09-22 23:09       ` Jonathan Tan
  2020-08-25 18:36     ` [PATCH v3 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
                       ` (8 subsequent siblings)
  10 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-25 18:36 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

One goal of background maintenance jobs is to allow a user to
disable auto-gc (gc.auto=0) but keep their repository in a clean
state. Without any cleanup, loose objects will clutter the object
database and slow operations. In addition, the loose objects will
take up extra space because they are not stored with deltas against
similar objects.

Create a 'loose-objects' task for the 'git maintenance run' command.
This helps clean up loose objects without disrupting concurrent Git
commands using the following sequence of events:

1. Run 'git prune-packed' to delete any loose objects that exist
   in a pack-file. Concurrent commands will prefer the packed
   version of the object to the loose version. (Of course, there
   are exceptions for commands that specifically care about the
   location of an object. These are rare for a user to run on
   purpose, and we hope a user that has selected background
   maintenance will not be trying to do foreground maintenance.)

2. Run 'git pack-objects' on a batch of loose objects. These
   objects are grouped by scanning the loose object directories in
   lexicographic order until listing all loose objects -or-
   reaching 50,000 objects. This is more than enough if the loose
   objects are created only by a user doing normal development.
   We noticed users with _millions_ of loose objects because VFS
   for Git downloads blobs on-demand when a file read operation
   requires populating a virtual file. This has potential of
   happening in partial clones if someone runs 'git grep' or
   otherwise evades the batch-download feature for requesting
   promisor objects.

This step is based on a similar step in Scalar [1] and VFS for Git.
[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/LooseObjectsStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 15 +++++
 builtin/gc.c                      | 97 +++++++++++++++++++++++++++++++
 t/t7900-maintenance.sh            | 39 +++++++++++++
 3 files changed, 151 insertions(+)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 12668fccf7..fc95eb594f 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -70,6 +70,21 @@ gc::
 	be disruptive in some situations, as it deletes stale data. See
 	linkgit:git-gc[1] for more details on garbage collection in Git.
 
+loose-objects::
+	The `loose-objects` job cleans up loose objects and places them into
+	pack-files. In order to prevent race conditions with concurrent Git
+	commands, it follows a two-step process. First, it deletes any loose
+	objects that already exist in a pack-file; concurrent Git processes
+	will examine the pack-file for the object data instead of the loose
+	object. Second, it creates a new pack-file (starting with "loose-")
+	containing a batch of loose objects. The batch size is limited to 50
+	thousand objects to prevent the job from taking too long on a
+	repository with many loose objects. The `gc` task writes unreachable
+	objects as loose objects to be cleaned up by a later step only if
+	they are not re-added to a pack-file; for this reason it is not
+	advisable to enable both the `loose-objects` and `gc` tasks at the
+	same time.
+
 OPTIONS
 -------
 --auto::
diff --git a/builtin/gc.c b/builtin/gc.c
index eb9c4d6147..248ccde3c3 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -880,6 +880,98 @@ static int maintenance_task_gc(struct maintenance_run_opts *opts)
 	return run_command(&child);
 }
 
+static int prune_packed(struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_push(&child.args, "prune-packed");
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--quiet");
+
+	return !!run_command(&child);
+}
+
+struct write_loose_object_data {
+	FILE *in;
+	int count;
+	int batch_size;
+};
+
+static int bail_on_loose(const struct object_id *oid,
+			 const char *path,
+			 void *data)
+{
+	return 1;
+}
+
+static int write_loose_object_to_stdin(const struct object_id *oid,
+				       const char *path,
+				       void *data)
+{
+	struct write_loose_object_data *d = (struct write_loose_object_data *)data;
+
+	fprintf(d->in, "%s\n", oid_to_hex(oid));
+
+	return ++(d->count) > d->batch_size;
+}
+
+static int pack_loose(struct maintenance_run_opts *opts)
+{
+	struct repository *r = the_repository;
+	int result = 0;
+	struct write_loose_object_data data;
+	struct child_process pack_proc = CHILD_PROCESS_INIT;
+
+	/*
+	 * Do not start pack-objects process
+	 * if there are no loose objects.
+	 */
+	if (!for_each_loose_file_in_objdir(r->objects->odb->path,
+					   bail_on_loose,
+					   NULL, NULL, NULL))
+		return 0;
+
+	pack_proc.git_cmd = 1;
+
+	strvec_push(&pack_proc.args, "pack-objects");
+	if (opts->quiet)
+		strvec_push(&pack_proc.args, "--quiet");
+	strvec_pushf(&pack_proc.args, "%s/pack/loose", r->objects->odb->path);
+
+	pack_proc.in = -1;
+
+	if (start_command(&pack_proc)) {
+		error(_("failed to start 'git pack-objects' process"));
+		return 1;
+	}
+
+	data.in = xfdopen(pack_proc.in, "w");
+	data.count = 0;
+	data.batch_size = 50000;
+
+	for_each_loose_file_in_objdir(r->objects->odb->path,
+				      write_loose_object_to_stdin,
+				      NULL,
+				      NULL,
+				      &data);
+
+	fclose(data.in);
+
+	if (finish_command(&pack_proc)) {
+		error(_("failed to finish 'git pack-objects' process"));
+		result = 1;
+	}
+
+	return result;
+}
+
+static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
+{
+	return prune_packed(opts) || pack_loose(opts);
+}
+
 typedef int maintenance_task_fn(struct maintenance_run_opts *opts);
 
 /*
@@ -901,6 +993,7 @@ struct maintenance_task {
 
 enum maintenance_task_label {
 	TASK_PREFETCH,
+	TASK_LOOSE_OBJECTS,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -913,6 +1006,10 @@ static struct maintenance_task tasks[] = {
 		"prefetch",
 		maintenance_task_prefetch,
 	},
+	[TASK_LOOSE_OBJECTS] = {
+		"loose-objects",
+		maintenance_task_loose_objects,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 0bade09c43..2e9e369786 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -86,4 +86,43 @@ test_expect_success 'prefetch multiple remotes' '
 	test_cmp_rev refs/remotes/remote2/two refs/prefetch/remote2/two
 '
 
+test_expect_success 'loose-objects task' '
+	# Repack everything so we know the state of the object dir
+	git repack -adk &&
+
+	# Hack to stop maintenance from running during "git commit"
+	echo in use >.git/objects/maintenance.lock &&
+
+	# Assuming that "git commit" creates at least one loose object
+	test_commit create-loose-object &&
+	rm .git/objects/maintenance.lock &&
+
+	ls .git/objects >obj-dir-before &&
+	test_file_not_empty obj-dir-before &&
+	ls .git/objects/pack/*.pack >packs-before &&
+	test_line_count = 1 packs-before &&
+
+	# The first run creates a pack-file
+	# but does not delete loose objects.
+	git maintenance run --task=loose-objects &&
+	ls .git/objects >obj-dir-between &&
+	test_cmp obj-dir-before obj-dir-between &&
+	ls .git/objects/pack/*.pack >packs-between &&
+	test_line_count = 2 packs-between &&
+	ls .git/objects/pack/loose-*.pack >loose-packs &&
+	test_line_count = 1 loose-packs &&
+
+	# The second run deletes loose objects
+	# but does not create a pack-file.
+	git maintenance run --task=loose-objects &&
+	ls .git/objects >obj-dir-after &&
+	cat >expect <<-\EOF &&
+	info
+	pack
+	EOF
+	test_cmp expect obj-dir-after &&
+	ls .git/objects/pack/*.pack >packs-after &&
+	test_cmp packs-between packs-after
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3 3/8] maintenance: create auto condition for loose-objects
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
  2020-08-25 18:36     ` [PATCH v3 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
  2020-08-25 18:36     ` [PATCH v3 2/8] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
@ 2020-08-25 18:36     ` Derrick Stolee via GitGitGadget
  2020-09-22 23:15       ` Jonathan Tan
  2020-08-25 18:36     ` [PATCH v3 4/8] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
                       ` (7 subsequent siblings)
  10 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-25 18:36 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The loose-objects task deletes loose objects that already exist in a
pack-file, then place the remaining loose objects into a new pack-file.
If this step runs all the time, then we risk creating pack-files with
very few objects with every 'git commit' process. To prevent
overwhelming the packs directory with small pack-files, place a minimum
number of objects to justify the task.

The 'maintenance.loose-objects.auto' config option specifies a minimum
number of loose objects to justify the task to run under the '--auto'
option. This defaults to 100 loose objects. Setting the value to zero
will prevent the step from running under '--auto' while a negative value
will force it to run every time.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/maintenance.txt |  9 +++++++++
 builtin/gc.c                         | 30 ++++++++++++++++++++++++++++
 t/t7900-maintenance.sh               | 25 +++++++++++++++++++++++
 3 files changed, 64 insertions(+)

diff --git a/Documentation/config/maintenance.txt b/Documentation/config/maintenance.txt
index 7cc6700d57..c31613be62 100644
--- a/Documentation/config/maintenance.txt
+++ b/Documentation/config/maintenance.txt
@@ -14,3 +14,12 @@ maintenance.commit-graph.auto::
 	reachable commits that are not in the commit-graph file is at least
 	the value of `maintenance.commit-graph.auto`. The default value is
 	100.
+
+maintenance.loose-objects.auto::
+	This integer config option controls how often the `loose-objects` task
+	should be run as part of `git maintenance run --auto`. If zero, then
+	the `loose-objects` task will not run with the `--auto` option. A
+	negative value will force the task to run every time. Otherwise, a
+	positive value implies the command should run when the number of
+	loose objects is at least the value of `maintenance.loose-objects.auto`.
+	The default value is 100.
diff --git a/builtin/gc.c b/builtin/gc.c
index 248ccde3c3..25245bcc10 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -899,6 +899,35 @@ struct write_loose_object_data {
 	int batch_size;
 };
 
+static int loose_object_auto_limit = 100;
+
+static int loose_object_count(const struct object_id *oid,
+			       const char *path,
+			       void *data)
+{
+	int *count = (int*)data;
+	if (++(*count) >= loose_object_auto_limit)
+		return 1;
+	return 0;
+}
+
+static int loose_object_auto_condition(void)
+{
+	int count = 0;
+
+	git_config_get_int("maintenance.loose-objects.auto",
+			   &loose_object_auto_limit);
+
+	if (!loose_object_auto_limit)
+		return 0;
+	if (loose_object_auto_limit < 0)
+		return 1;
+
+	return for_each_loose_file_in_objdir(the_repository->objects->odb->path,
+					     loose_object_count,
+					     NULL, NULL, &count);
+}
+
 static int bail_on_loose(const struct object_id *oid,
 			 const char *path,
 			 void *data)
@@ -1009,6 +1038,7 @@ static struct maintenance_task tasks[] = {
 	[TASK_LOOSE_OBJECTS] = {
 		"loose-objects",
 		maintenance_task_loose_objects,
+		loose_object_auto_condition,
 	},
 	[TASK_GC] = {
 		"gc",
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 2e9e369786..efda1cf69b 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -125,4 +125,29 @@ test_expect_success 'loose-objects task' '
 	test_cmp packs-between packs-after
 '
 
+test_expect_success 'maintenance.loose-objects.auto' '
+	git repack -adk &&
+	GIT_TRACE2_EVENT="$(pwd)/trace-lo1.txt" \
+		git -c maintenance.loose-objects.auto=1 maintenance \
+		run --auto --task=loose-objects 2>/dev/null &&
+	test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
+	for i in 1 2
+	do
+		printf data-A-$i | git hash-object -t blob --stdin -w &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-loA-$i" \
+			git -c maintenance.loose-objects.auto=2 \
+			maintenance run --auto --task=loose-objects 2>/dev/null &&
+		test_subcommand ! git prune-packed --quiet <trace-loA-$i &&
+		printf data-B-$i | git hash-object -t blob --stdin -w &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-loB-$i" \
+			git -c maintenance.loose-objects.auto=2 \
+			maintenance run --auto --task=loose-objects 2>/dev/null &&
+		test_subcommand git prune-packed --quiet <trace-loB-$i &&
+		GIT_TRACE2_EVENT="$(pwd)/trace-loC-$i" \
+			git -c maintenance.loose-objects.auto=2 \
+			maintenance run --auto --task=loose-objects 2>/dev/null &&
+		test_subcommand git prune-packed --quiet <trace-loC-$i || return 1
+	done
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3 4/8] midx: enable core.multiPackIndex by default
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                       ` (2 preceding siblings ...)
  2020-08-25 18:36     ` [PATCH v3 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
@ 2020-08-25 18:36     ` Derrick Stolee via GitGitGadget
  2020-09-22 23:16       ` Jonathan Tan
  2020-08-25 18:36     ` [PATCH v3 5/8] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
                       ` (6 subsequent siblings)
  10 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-25 18:36 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The core.multiPackIndex setting has been around since c4d25228ebb
(config: create core.multiPackIndex setting, 2018-07-12), but has been
disabled by default. If a user wishes to use the multi-pack-index
feature, then they must enable this config and run 'git multi-pack-index
write'.

The multi-pack-index feature is relatively stable now, so make the
config option true by default. For users that do not use a
multi-pack-index, the only extra cost will be a file lookup to see if a
multi-pack-index file exists (once per process, per object directory).

Also, this config option will be referenced by an upcoming
"incremental-repack" task in the maintenance builtin, so move the config
option into the repository settings struct. Note that if
GIT_TEST_MULTI_PACK_INDEX=1, then we want to ignore the config option
and treat core.multiPackIndex as enabled.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/core.txt |  4 ++--
 midx.c                        | 11 +++--------
 repo-settings.c               |  6 ++++++
 repository.h                  |  2 ++
 4 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 74619a9c03..86c91d5381 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -606,8 +606,8 @@ core.useReplaceRefs::
 
 core.multiPackIndex::
 	Use the multi-pack-index file to track multiple packfiles using a
-	single index. See link:technical/multi-pack-index.html[the
-	multi-pack-index design document].
+	single index. See linkgit:git-multi-pack-index[1] for more
+	information. Defaults to true.
 
 core.sparseCheckout::
 	Enable "sparse checkout" feature. See linkgit:git-sparse-checkout[1]
diff --git a/midx.c b/midx.c
index a5fb797ede..ef499cf504 100644
--- a/midx.c
+++ b/midx.c
@@ -10,6 +10,7 @@
 #include "progress.h"
 #include "trace2.h"
 #include "run-command.h"
+#include "repository.h"
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
@@ -384,15 +385,9 @@ int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, i
 {
 	struct multi_pack_index *m;
 	struct multi_pack_index *m_search;
-	int config_value;
-	static int env_value = -1;
 
-	if (env_value < 0)
-		env_value = git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0);
-
-	if (!env_value &&
-	    (repo_config_get_bool(r, "core.multipackindex", &config_value) ||
-	    !config_value))
+	prepare_repo_settings(r);
+	if (!r->settings.core_multi_pack_index)
 		return 0;
 
 	for (m_search = r->objects->multi_pack_index; m_search; m_search = m_search->next)
diff --git a/repo-settings.c b/repo-settings.c
index 0918408b34..5bd2c22726 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -1,6 +1,7 @@
 #include "cache.h"
 #include "config.h"
 #include "repository.h"
+#include "midx.h"
 
 #define UPDATE_DEFAULT_BOOL(s,v) do { if (s == -1) { s = v; } } while(0)
 
@@ -47,6 +48,11 @@ void prepare_repo_settings(struct repository *r)
 		r->settings.pack_use_sparse = value;
 	UPDATE_DEFAULT_BOOL(r->settings.pack_use_sparse, 1);
 
+	value = git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0);
+	if (value || !repo_config_get_bool(r, "core.multipackindex", &value))
+		r->settings.core_multi_pack_index = value;
+	UPDATE_DEFAULT_BOOL(r->settings.core_multi_pack_index, 1);
+
 	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
 		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
diff --git a/repository.h b/repository.h
index 3c1f7d54bd..3901ce0b65 100644
--- a/repository.h
+++ b/repository.h
@@ -37,6 +37,8 @@ struct repo_settings {
 
 	int pack_use_sparse;
 	enum fetch_negotiation_setting fetch_negotiation_algorithm;
+
+	int core_multi_pack_index;
 };
 
 struct repository {
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3 5/8] midx: use start_delayed_progress()
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                       ` (3 preceding siblings ...)
  2020-08-25 18:36     ` [PATCH v3 4/8] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
@ 2020-08-25 18:36     ` Derrick Stolee via GitGitGadget
  2020-08-25 18:36     ` [PATCH v3 6/8] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
                       ` (5 subsequent siblings)
  10 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-25 18:36 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

Now that the multi-pack-index may be written as part of auto maintenance
at the end of a command, reduce the progress output when the operations
are quick. Use start_delayed_progress() instead of start_progress().

Update t5319-multi-pack-index.sh to use GIT_PROGRESS_DELAY=0 now that
the progress indicators are conditional.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 midx.c                      | 10 +++++-----
 t/t5319-multi-pack-index.sh | 14 +++++++-------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/midx.c b/midx.c
index ef499cf504..aa37d5da86 100644
--- a/midx.c
+++ b/midx.c
@@ -832,7 +832,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 
 	packs.pack_paths_checked = 0;
 	if (flags & MIDX_PROGRESS)
-		packs.progress = start_progress(_("Adding packfiles to multi-pack-index"), 0);
+		packs.progress = start_delayed_progress(_("Adding packfiles to multi-pack-index"), 0);
 	else
 		packs.progress = NULL;
 
@@ -969,7 +969,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 	}
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Writing chunks to multi-pack-index"),
+		progress = start_delayed_progress(_("Writing chunks to multi-pack-index"),
 					  num_chunks);
 	for (i = 0; i < num_chunks; i++) {
 		if (written != chunk_offsets[i])
@@ -1104,7 +1104,7 @@ int verify_midx_file(struct repository *r, const char *object_dir, unsigned flag
 		return 0;
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Looking for referenced packfiles"),
+		progress = start_delayed_progress(_("Looking for referenced packfiles"),
 					  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
 		if (prepare_midx_pack(r, m, i))
@@ -1225,7 +1225,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 	count = xcalloc(m->num_packs, sizeof(uint32_t));
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Counting referenced objects"),
+		progress = start_delayed_progress(_("Counting referenced objects"),
 					  m->num_objects);
 	for (i = 0; i < m->num_objects; i++) {
 		int pack_int_id = nth_midxed_pack_int_id(m, i);
@@ -1235,7 +1235,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 	stop_progress(&progress);
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Finding and deleting unreferenced packfiles"),
+		progress = start_delayed_progress(_("Finding and deleting unreferenced packfiles"),
 					  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
 		char *pack_name;
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 7dfff0f8f4..ec87f616c6 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -171,12 +171,12 @@ test_expect_success 'write progress off for redirected stderr' '
 '
 
 test_expect_success 'write force progress on for stderr' '
-	git multi-pack-index --object-dir=$objdir --progress write 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --progress write 2>err &&
 	test_file_not_empty err
 '
 
 test_expect_success 'write with the --no-progress option' '
-	git multi-pack-index --object-dir=$objdir --no-progress write 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --no-progress write 2>err &&
 	test_line_count = 0 err
 '
 
@@ -333,17 +333,17 @@ test_expect_success 'git-fsck incorrect offset' '
 '
 
 test_expect_success 'repack progress off for redirected stderr' '
-	git multi-pack-index --object-dir=$objdir repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir repack 2>err &&
 	test_line_count = 0 err
 '
 
 test_expect_success 'repack force progress on for stderr' '
-	git multi-pack-index --object-dir=$objdir --progress repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --progress repack 2>err &&
 	test_file_not_empty err
 '
 
 test_expect_success 'repack with the --no-progress option' '
-	git multi-pack-index --object-dir=$objdir --no-progress repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --no-progress repack 2>err &&
 	test_line_count = 0 err
 '
 
@@ -487,7 +487,7 @@ test_expect_success 'expire progress off for redirected stderr' '
 test_expect_success 'expire force progress on for stderr' '
 	(
 		cd dup &&
-		git multi-pack-index --progress expire 2>err &&
+		GIT_PROGRESS_DELAY=0 git multi-pack-index --progress expire 2>err &&
 		test_file_not_empty err
 	)
 '
@@ -495,7 +495,7 @@ test_expect_success 'expire force progress on for stderr' '
 test_expect_success 'expire with the --no-progress option' '
 	(
 		cd dup &&
-		git multi-pack-index --no-progress expire 2>err &&
+		GIT_PROGRESS_DELAY=0 git multi-pack-index --no-progress expire 2>err &&
 		test_line_count = 0 err
 	)
 '
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3 6/8] maintenance: add incremental-repack task
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                       ` (4 preceding siblings ...)
  2020-08-25 18:36     ` [PATCH v3 5/8] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
@ 2020-08-25 18:36     ` Derrick Stolee via GitGitGadget
  2020-09-22 23:26       ` Jonathan Tan
  2020-08-25 18:36     ` [PATCH v3 7/8] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
                       ` (4 subsequent siblings)
  10 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-25 18:36 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The previous change cleaned up loose objects using the
'loose-objects' that can be run safely in the background. Add a
similar job that performs similar cleanups for pack-files.

One issue with running 'git repack' is that it is designed to
repack all pack-files into a single pack-file. While this is the
most space-efficient way to store object data, it is not time or
memory efficient. This becomes extremely important if the repo is
so large that a user struggles to store two copies of the pack on
their disk.

Instead, perform an "incremental" repack by collecting a few small
pack-files into a new pack-file. The multi-pack-index facilitates
this process ever since 'git multi-pack-index expire' was added in
19575c7 (multi-pack-index: implement 'expire' subcommand,
2019-06-10) and 'git multi-pack-index repack' was added in ce1e4a1
(midx: implement midx_repack(), 2019-06-10).

The 'incremental-repack' task runs the following steps:

1. 'git multi-pack-index write' creates a multi-pack-index file if
   one did not exist, and otherwise will update the multi-pack-index
   with any new pack-files that appeared since the last write. This
   is particularly relevant with the background fetch job.

   When the multi-pack-index sees two copies of the same object, it
   stores the offset data into the newer pack-file. This means that
   some old pack-files could become "unreferenced" which I will use
   to mean "a pack-file that is in the pack-file list of the
   multi-pack-index but none of the objects in the multi-pack-index
   reference a location inside that pack-file."

2. 'git multi-pack-index expire' deletes any unreferenced pack-files
   and updaes the multi-pack-index to drop those pack-files from the
   list. This is safe to do as concurrent Git processes will see the
   multi-pack-index and not open those packs when looking for object
   contents. (Similar to the 'loose-objects' job, there are some Git
   commands that open pack-files regardless of the multi-pack-index,
   but they are rarely used. Further, a user that self-selects to
   use background operations would likely refrain from using those
   commands.)

3. 'git multi-pack-index repack --bacth-size=<size>' collects a set
   of pack-files that are listed in the multi-pack-index and creates
   a new pack-file containing the objects whose offsets are listed
   by the multi-pack-index to be in those objects. The set of pack-
   files is selected greedily by sorting the pack-files by modified
   time and adding a pack-file to the set if its "expected size" is
   smaller than the batch size until the total expected size of the
   selected pack-files is at least the batch size. The "expected
   size" is calculated by taking the size of the pack-file divided
   by the number of objects in the pack-file and multiplied by the
   number of objects from the multi-pack-index with offset in that
   pack-file. The expected size approximates how much data from that
   pack-file will contribute to the resulting pack-file size. The
   intention is that the resulting pack-file will be close in size
   to the provided batch size.

   The next run of the incremental-repack task will delete these
   repacked pack-files during the 'expire' step.

   In this version, the batch size is set to "0" which ignores the
   size restrictions when selecting the pack-files. It instead
   selects all pack-files and repacks all packed objects into a
   single pack-file. This will be updated in the next change, but
   it requires doing some calculations that are better isolated to
   a separate change.

These steps are based on a similar background maintenance step in
Scalar (and VFS for Git) [1]. This was incredibly effective for
users of the Windows OS repository. After using the same VFS for Git
repository for over a year, some users had _thousands_ of pack-files
that combined to up to 250 GB of data. We noticed a few users were
running into the open file descriptor limits (due in part to a bug
in the multi-pack-index fixed by af96fe3 (midx: add packs to
packed_git linked list, 2019-04-29).

These pack-files were mostly small since they contained the commits
and trees that were pushed to the origin in a given hour. The GVFS
protocol includes a "prefetch" step that asks for pre-computed pack-
files containing commits and trees by timestamp. These pack-files
were grouped into "daily" pack-files once a day for up to 30 days.
If a user did not request prefetch packs for over 30 days, then they
would get the entire history of commits and trees in a new, large
pack-file. This led to a large number of pack-files that had poor
delta compression.

By running this pack-file maintenance step once per day, these repos
with thousands of packs spanning 200+ GB dropped to dozens of pack-
files spanning 30-50 GB. This was done all without removing objects
from the system and using a constant batch size of two gigabytes.
Once the work was done to reduce the pack-files to small sizes, the
batch size of two gigabytes means that not every run triggers a
repack operation, so the following run will not expire a pack-file.
This has kept these repos in a "clean" state.

[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/PackfileMaintenanceStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 15 ++++++
 builtin/gc.c                      | 77 +++++++++++++++++++++++++++++++
 midx.c                            |  2 +-
 midx.h                            |  1 +
 t/t5319-multi-pack-index.sh       |  1 +
 t/t7900-maintenance.sh            | 38 +++++++++++++++
 6 files changed, 133 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index fc95eb594f..b44efb05a3 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -85,6 +85,21 @@ loose-objects::
 	advisable to enable both the `loose-objects` and `gc` tasks at the
 	same time.
 
+incremental-repack::
+	The `incremental-repack` job repacks the object directory
+	using the `multi-pack-index` feature. In order to prevent race
+	conditions with concurrent Git commands, it follows a two-step
+	process. First, it deletes any pack-files included in the
+	`multi-pack-index` where none of the objects in the
+	`multi-pack-index` reference those pack-files; this only happens
+	if all objects in the pack-file are also stored in a newer
+	pack-file. Second, it selects a group of pack-files whose "expected
+	size" is below the batch size until the group has total expected
+	size at least the batch size; see the `--batch-size` option for
+	the `repack` subcommand in linkgit:git-multi-pack-index[1]. The
+	default batch-size is zero, which is a special case that attempts
+	to repack all pack-files into a single pack-file.
+
 OPTIONS
 -------
 --auto::
diff --git a/builtin/gc.c b/builtin/gc.c
index 25245bcc10..fbf84996fa 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -30,6 +30,7 @@
 #include "promisor-remote.h"
 #include "refs.h"
 #include "remote.h"
+#include "midx.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -1001,6 +1002,77 @@ static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
 	return prune_packed(opts) || pack_loose(opts);
 }
 
+static int multi_pack_index_write(struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "write", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	if (run_command(&child))
+		return error(_("failed to write multi-pack-index"));
+
+	return 0;
+}
+
+static int multi_pack_index_expire(struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "expire", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	close_object_store(the_repository->objects);
+
+	if (run_command(&child))
+		return error(_("'git multi-pack-index expire' failed"));
+
+	return 0;
+}
+
+static int multi_pack_index_repack(struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "repack", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	strvec_push(&child.args, "--batch-size=0");
+
+	close_object_store(the_repository->objects);
+
+	if (run_command(&child))
+		return error(_("'git multi-pack-index repack' failed"));
+
+	return 0;
+}
+
+static int maintenance_task_incremental_repack(struct maintenance_run_opts *opts)
+{
+	prepare_repo_settings(the_repository);
+	if (!the_repository->settings.core_multi_pack_index) {
+		warning(_("skipping incremental-repack task because core.multiPackIndex is disabled"));
+		return 0;
+	}
+
+	if (multi_pack_index_write(opts))
+		return 1;
+	if (multi_pack_index_expire(opts))
+		return 1;
+	if (multi_pack_index_repack(opts))
+		return 1;
+	return 0;
+}
+
 typedef int maintenance_task_fn(struct maintenance_run_opts *opts);
 
 /*
@@ -1023,6 +1095,7 @@ struct maintenance_task {
 enum maintenance_task_label {
 	TASK_PREFETCH,
 	TASK_LOOSE_OBJECTS,
+	TASK_INCREMENTAL_REPACK,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -1040,6 +1113,10 @@ static struct maintenance_task tasks[] = {
 		maintenance_task_loose_objects,
 		loose_object_auto_condition,
 	},
+	[TASK_INCREMENTAL_REPACK] = {
+		"incremental-repack",
+		maintenance_task_incremental_repack,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/midx.c b/midx.c
index aa37d5da86..66d7053d83 100644
--- a/midx.c
+++ b/midx.c
@@ -37,7 +37,7 @@
 
 #define PACK_EXPIRED UINT_MAX
 
-static char *get_midx_filename(const char *object_dir)
+char *get_midx_filename(const char *object_dir)
 {
 	return xstrfmt("%s/pack/multi-pack-index", object_dir);
 }
diff --git a/midx.h b/midx.h
index b18cf53bc4..baeecc70c9 100644
--- a/midx.h
+++ b/midx.h
@@ -37,6 +37,7 @@ struct multi_pack_index {
 
 #define MIDX_PROGRESS     (1 << 0)
 
+char *get_midx_filename(const char *object_dir);
 struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local);
 int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
 int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result);
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index ec87f616c6..2f942ee1fa 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -3,6 +3,7 @@
 test_description='multi-pack-indexes'
 . ./test-lib.sh
 
+GIT_TEST_MULTI_PACK_INDEX=0
 objdir=.git/objects
 
 midx_read_expect () {
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index efda1cf69b..dde28cf837 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -5,6 +5,7 @@ test_description='git maintenance builtin'
 . ./test-lib.sh
 
 GIT_TEST_COMMIT_GRAPH=0
+GIT_TEST_MULTI_PACK_INDEX=0
 
 test_expect_success 'help text' '
 	test_expect_code 129 git maintenance -h 2>err &&
@@ -150,4 +151,41 @@ test_expect_success 'maintenance.loose-objects.auto' '
 	done
 '
 
+test_expect_success 'incremental-repack task' '
+	packDir=.git/objects/pack &&
+	for i in $(test_seq 1 5)
+	do
+		test_commit $i || return 1
+	done &&
+
+	# Create three disjoint pack-files with size BIG, small, small.
+	echo HEAD~2 | git pack-objects --revs $packDir/test-1 &&
+	test_tick &&
+	git pack-objects --revs $packDir/test-2 <<-\EOF &&
+	HEAD~1
+	^HEAD~2
+	EOF
+	test_tick &&
+	git pack-objects --revs $packDir/test-3 <<-\EOF &&
+	HEAD
+	^HEAD~1
+	EOF
+	rm -f $packDir/pack-* &&
+	rm -f $packDir/loose-* &&
+	ls $packDir/*.pack >packs-before &&
+	test_line_count = 3 packs-before &&
+
+	# the job repacks the two into a new pack, but does not
+	# delete the old ones.
+	git maintenance run --task=incremental-repack &&
+	ls $packDir/*.pack >packs-between &&
+	test_line_count = 4 packs-between &&
+
+	# the job deletes the two old packs, and does not write
+	# a new one because only one pack remains.
+	git maintenance run --task=incremental-repack &&
+	ls .git/objects/pack/*.pack >packs-after &&
+	test_line_count = 1 packs-after
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3 7/8] maintenance: auto-size incremental-repack batch
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                       ` (5 preceding siblings ...)
  2020-08-25 18:36     ` [PATCH v3 6/8] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
@ 2020-08-25 18:36     ` Derrick Stolee via GitGitGadget
  2020-08-25 18:36     ` [PATCH v3 8/8] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
                       ` (3 subsequent siblings)
  10 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-25 18:36 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

When repacking during the 'incremental-repack' task, we use the
--batch-size option in 'git multi-pack-index repack'. The initial setting
used --batch-size=0 to repack everything into a single pack-file. This is
not sustainable for a large repository. The amount of work required is
also likely to use too many system resources for a background job.

Update the 'incremental-repack' task by dynamically computing a
--batch-size option based on the current pack-file structure.

The dynamic default size is computed with this idea in mind for a client
repository that was cloned from a very large remote: there is likely one
"big" pack-file that was created at clone time. Thus, do not try
repacking it as it is likely packed efficiently by the server.

Instead, we select the second-largest pack-file, and create a batch size
that is one larger than that pack-file. If there are three or more
pack-files, then this guarantees that at least two will be combined into
a new pack-file.

Of course, this means that the second-largest pack-file size is likely
to grow over time and may eventually surpass the initially-cloned
pack-file. Recall that the pack-file batch is selected in a greedy
manner: the packs are considered from oldest to newest and are selected
if they have size smaller than the batch size until the total selected
size is larger than the batch size. Thus, that oldest "clone" pack will
be first to repack after the new data creates a pack larger than that.

We also want to place some limits on how large these pack-files become,
in order to bound the amount of time spent repacking. A maximum
batch-size of two gigabytes means that large repositories will never be
packed into a single pack-file using this job, but also that repack is
rather expensive. This is a trade-off that is valuable to have if the
maintenance is being run automatically or in the background. Users who
truly want to optimize for space and performance (and are willing to pay
the upfront cost of a full repack) can use the 'gc' task to do so.

Create a test for this two gigabyte limit by creating an EXPENSIVE test
that generates two pack-files of roughly 2.5 gigabytes in size, then
performs an incremental repack. Check that the --batch-size argument in
the subcommand uses the hard-coded maximum.

Helped-by: Chris Torek <chris.torek@gmail.com>
Reported-by: Son Luong Ngoc <sluongng@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 builtin/gc.c           | 43 +++++++++++++++++++++++++++++++++++++++++-
 t/t7900-maintenance.sh | 36 +++++++++++++++++++++++++++++++++--
 2 files changed, 76 insertions(+), 3 deletions(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index fbf84996fa..e043403400 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1036,6 +1036,46 @@ static int multi_pack_index_expire(struct maintenance_run_opts *opts)
 	return 0;
 }
 
+#define TWO_GIGABYTES (INT32_MAX)
+
+static off_t get_auto_pack_size(void)
+{
+	/*
+	 * The "auto" value is special: we optimize for
+	 * one large pack-file (i.e. from a clone) and
+	 * expect the rest to be small and they can be
+	 * repacked quickly.
+	 *
+	 * The strategy we select here is to select a
+	 * size that is one more than the second largest
+	 * pack-file. This ensures that we will repack
+	 * at least two packs if there are three or more
+	 * packs.
+	 */
+	off_t max_size = 0;
+	off_t second_largest_size = 0;
+	off_t result_size;
+	struct packed_git *p;
+	struct repository *r = the_repository;
+
+	reprepare_packed_git(r);
+	for (p = get_all_packs(r); p; p = p->next) {
+		if (p->pack_size > max_size) {
+			second_largest_size = max_size;
+			max_size = p->pack_size;
+		} else if (p->pack_size > second_largest_size)
+			second_largest_size = p->pack_size;
+	}
+
+	result_size = second_largest_size + 1;
+
+	/* But limit ourselves to a batch size of 2g */
+	if (result_size > TWO_GIGABYTES)
+		result_size = TWO_GIGABYTES;
+
+	return result_size;
+}
+
 static int multi_pack_index_repack(struct maintenance_run_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -1046,7 +1086,8 @@ static int multi_pack_index_repack(struct maintenance_run_opts *opts)
 	if (opts->quiet)
 		strvec_push(&child.args, "--no-progress");
 
-	strvec_push(&child.args, "--batch-size=0");
+	strvec_pushf(&child.args, "--batch-size=%"PRIuMAX,
+				  (uintmax_t)get_auto_pack_size());
 
 	close_object_store(the_repository->objects);
 
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index dde28cf837..5c08afc19a 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -182,10 +182,42 @@ test_expect_success 'incremental-repack task' '
 	test_line_count = 4 packs-between &&
 
 	# the job deletes the two old packs, and does not write
-	# a new one because only one pack remains.
+	# a new one because the batch size is not high enough to
+	# pack the largest pack-file.
 	git maintenance run --task=incremental-repack &&
 	ls .git/objects/pack/*.pack >packs-after &&
-	test_line_count = 1 packs-after
+	test_line_count = 2 packs-after
+'
+
+test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
+	for i in $(test_seq 1 5)
+	do
+		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
+		return 1
+	done &&
+	git add big &&
+	git commit -m "Add big file (1)" &&
+
+	# ensure any possible loose objects are in a pack-file
+	git maintenance run --task=loose-objects &&
+
+	rm big &&
+	for i in $(test_seq 6 10)
+	do
+		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
+		return 1
+	done &&
+	git add big &&
+	git commit -m "Add big file (2)" &&
+
+	# ensure any possible loose objects are in a pack-file
+	git maintenance run --task=loose-objects &&
+
+	# Now run the incremental-repack task and check the batch-size
+	GIT_TRACE2_EVENT="$(pwd)/run-2g.txt" git maintenance run \
+		--task=incremental-repack 2>/dev/null &&
+	test_subcommand git multi-pack-index repack \
+		 --no-progress --batch-size=2147483647 <run-2g.txt
 '
 
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v3 8/8] maintenance: add incremental-repack auto condition
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                       ` (6 preceding siblings ...)
  2020-08-25 18:36     ` [PATCH v3 7/8] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
@ 2020-08-25 18:36     ` Derrick Stolee via GitGitGadget
  2020-09-22 23:52       ` Jonathan Tan
  2020-08-25 20:59     ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Junio C Hamano
                       ` (2 subsequent siblings)
  10 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-08-25 18:36 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Derrick Stolee,
	Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The incremental-repack task updates the multi-pack-index by deleting pack-
files that have been replaced with new packs, then repacking a batch of
small pack-files into a larger pack-file. This incremental repack is faster
than rewriting all object data, but is slower than some other
maintenance activities.

The 'maintenance.incremental-repack.auto' config option specifies how many
pack-files should exist outside of the multi-pack-index before running
the step. These pack-files could be created by 'git fetch' commands or
by the loose-objects task. The default value is 10.

Setting the option to zero disables the task with the '--auto' option,
and a negative value makes the task run every time.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/maintenance.txt |  9 ++++++++
 builtin/gc.c                         | 31 ++++++++++++++++++++++++++++
 t/t7900-maintenance.sh               | 31 ++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+)

diff --git a/Documentation/config/maintenance.txt b/Documentation/config/maintenance.txt
index c31613be62..a0706d8f09 100644
--- a/Documentation/config/maintenance.txt
+++ b/Documentation/config/maintenance.txt
@@ -23,3 +23,12 @@ maintenance.loose-objects.auto::
 	positive value implies the command should run when the number of
 	loose objects is at least the value of `maintenance.loose-objects.auto`.
 	The default value is 100.
+
+maintenance.incremental-repack.auto::
+	This integer config option controls how often the `incremental-repack`
+	task should be run as part of `git maintenance run --auto`. If zero,
+	then the `incremental-repack` task will not run with the `--auto`
+	option. A negative value will force the task to run every time.
+	Otherwise, a positive value implies the command should run when the
+	number of pack-files not in the multi-pack-index is at least the value
+	of `maintenance.incremental-repack.auto`. The default value is 10.
diff --git a/builtin/gc.c b/builtin/gc.c
index e043403400..f8459df04c 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -31,6 +31,7 @@
 #include "refs.h"
 #include "remote.h"
 #include "midx.h"
+#include "object-store.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -1002,6 +1003,35 @@ static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
 	return prune_packed(opts) || pack_loose(opts);
 }
 
+static int incremental_repack_auto_condition(void)
+{
+	struct packed_git *p;
+	int enabled;
+	int incremental_repack_auto_limit = 10;
+	int count = 0;
+
+	if (git_config_get_bool("core.multiPackIndex", &enabled) ||
+	    !enabled)
+		return 0;
+
+	git_config_get_int("maintenance.incremental-repack.auto",
+			   &incremental_repack_auto_limit);
+
+	if (!incremental_repack_auto_limit)
+		return 0;
+	if (incremental_repack_auto_limit < 0)
+		return 1;
+
+	for (p = get_packed_git(the_repository);
+	     count < incremental_repack_auto_limit && p;
+	     p = p->next) {
+		if (!p->multi_pack_index)
+			count++;
+	}
+
+	return count >= incremental_repack_auto_limit;
+}
+
 static int multi_pack_index_write(struct maintenance_run_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -1157,6 +1187,7 @@ static struct maintenance_task tasks[] = {
 	[TASK_INCREMENTAL_REPACK] = {
 		"incremental-repack",
 		maintenance_task_incremental_repack,
+		incremental_repack_auto_condition,
 	},
 	[TASK_GC] = {
 		"gc",
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 5c08afc19a..6f878b0141 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -220,4 +220,35 @@ test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
 		 --no-progress --batch-size=2147483647 <run-2g.txt
 '
 
+test_expect_success 'maintenance.incremental-repack.auto' '
+	git repack -adk &&
+	git config core.multiPackIndex true &&
+	git multi-pack-index write &&
+	GIT_TRACE2_EVENT="$(pwd)/midx-init.txt" git \
+		-c maintenance.incremental-repack.auto=1 \
+		maintenance run --auto --task=incremental-repack 2>/dev/null &&
+	test_subcommand ! git multi-pack-index write --no-progress <midx-init.txt &&
+	for i in 1 2
+	do
+		test_commit A-$i &&
+		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
+		HEAD
+		^HEAD~1
+		EOF
+		GIT_TRACE2_EVENT=$(pwd)/trace-A-$i git \
+			-c maintenance.incremental-repack.auto=2 \
+			maintenance run --auto --task=incremental-repack 2>/dev/null &&
+		test_subcommand ! git multi-pack-index write --no-progress <trace-A-$i &&
+		test_commit B-$i &&
+		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
+		HEAD
+		^HEAD~1
+		EOF
+		GIT_TRACE2_EVENT=$(pwd)/trace-B-$i git \
+			-c maintenance.incremental-repack.auto=2 \
+			maintenance run --auto --task=incremental-repack 2>/dev/null &&
+		test_subcommand git multi-pack-index write --no-progress <trace-B-$i || return 1
+	done
+'
+
 test_done
-- 
gitgitgadget

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                       ` (7 preceding siblings ...)
  2020-08-25 18:36     ` [PATCH v3 8/8] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
@ 2020-08-25 20:59     ` Junio C Hamano
  2020-08-26 15:15     ` Son Luong Ngoc
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
  10 siblings, 0 replies; 66+ messages in thread
From: Junio C Hamano @ 2020-08-25 20:59 UTC (permalink / raw)
  To: Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, jonathantanmy,
	Derrick Stolee

"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> This series is based on v3 of part I (ds/maintenance-part-1) [2].
>
> This patch series contains 9 patches that were going to be part of v4 of
> ds/maintenance [1], but the discussion has gotten really long. To help, I'm
> splitting out the portions that create and test the 'maintenance' builtin
> from the additional tasks (prefetch, loose-objects, incremental-repack) that
> can be brought in later.

I gave it a quick look but the changes mostly are fallout from
renaming the options structure to maitenance_RUN_opts and loss of
midx verify while a task rewrites midx; iow, no significant change
that are likely to become controversial.

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                       ` (8 preceding siblings ...)
  2020-08-25 20:59     ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Junio C Hamano
@ 2020-08-26 15:15     ` Son Luong Ngoc
  2020-08-26 16:21       ` Derrick Stolee
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
  10 siblings, 1 reply; 66+ messages in thread
From: Son Luong Ngoc @ 2020-08-26 15:15 UTC (permalink / raw)
  To: Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, Jeff King, congdanhqx,
	phillip.wood123, Emily Shaffer, Jonathan Tan, Derrick Stolee

Hi Derrick,

> On Aug 25, 2020, at 20:36, Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com> wrote:
> 

...

> 
> Updates since v2
> ================
> 
> * Dropped "fetch: optionally allow disabling FETCH_HEAD update"
> 
> 
> * A lot of fallout from the change in the option parsing in v3 of
>   Maintenance II.
> 
> 
> * Dropped the "verify, and delete and rewrite on failure" logic from the
>   incremental-repack task. This might be added again later after it can be
>   tested more thoroughly.

Perhaps I missed some conversations related to this change but
why was this verify-rewrite strategy dropped?

Was the problem such strategy were created to solve is now no longer a concern?

I feel like it would be much better to add it in and then remove it using a separated commit?
That way we can follow the reasoning behind these decisions via commit message.

> 

...

> 
> -- 
> gitgitgadget

Thanks,
Son Luong.

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks
  2020-08-26 15:15     ` Son Luong Ngoc
@ 2020-08-26 16:21       ` Derrick Stolee
  0 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee @ 2020-08-26 16:21 UTC (permalink / raw)
  To: Son Luong Ngoc, Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, Jeff King, congdanhqx,
	phillip.wood123, Emily Shaffer, Jonathan Tan, Derrick Stolee

On 8/26/2020 11:15 AM, Son Luong Ngoc wrote:
> Hi Derrick,
> 
>> On Aug 25, 2020, at 20:36, Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com> wrote:
>> * Dropped the "verify, and delete and rewrite on failure" logic from the
>>   incremental-repack task. This might be added again later after it can be
>>   tested more thoroughly.
> 
> Perhaps I missed some conversations related to this change but
> why was this verify-rewrite strategy dropped?
> 
> Was the problem such strategy were created to solve is now no longer a concern?
> 
> I feel like it would be much better to add it in and then remove it using a separated commit?
> That way we can follow the reasoning behind these decisions via commit message.

The most-recent message was [1]

[1] https://lore.kernel.org/git/20200819174322.3087791-1-jonathantanmy@google.com/

For now, I'd rather move forward with this simpler task
and I will revisit the "verify and fix" situation when
it can be done in a focused way instead of being surrounded
by builtin boilerplate and other basics of the maintenance
feature. Specifically, it would help to have a way to test
the logic. In Scalar, I was able to mock the Git commands
and return failures in specific places. A similar approach
could be done here, or perhaps there is another way to be
confident that the "verify and fix" logic is actually
helpful.

Thanks,
-Stolee

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 1/8] maintenance: add prefetch task
  2020-08-25 18:36     ` [PATCH v3 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
@ 2020-09-22 23:05       ` Jonathan Tan
  0 siblings, 0 replies; 66+ messages in thread
From: Jonathan Tan @ 2020-09-22 23:05 UTC (permalink / raw)
  To: gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, jonathantanmy,
	derrickstolee, dstolee

> From: Derrick Stolee <dstolee@microsoft.com>
> 
> When working with very large repositories, an incremental 'git fetch'
> command can download a large amount of data. If there are many other
> users pushing to a common repo, then this data can rival the initial
> pack-file size of a 'git clone' of a medium-size repo.
> 
> Users may want to keep the data on their local repos as close as
> possible to the data on the remote repos by fetching periodically in
> the background. This can break up a large daily fetch into several
> smaller hourly fetches.
> 
> The task is called "prefetch" because it is work done in advance
> of a foreground fetch to make that 'git fetch' command much faster.
> 
> However, if we simply ran 'git fetch <remote>' in the background,
> then the user running a foregroudn 'git fetch <remote>' would lose

-> foreground

I have some more minor comments that I will send as individual replies,
but overall, the patch set looks good to me.

> +static int append_remote(struct remote *remote, void *cbdata)
> +{
> +	struct string_list *remotes = (struct string_list *)cbdata;
> +
> +	string_list_append(remotes, remote->name);
> +	return 0;
> +}
> +
> +static int maintenance_task_prefetch(struct maintenance_run_opts *opts)
> +{
> +	int result = 0;
> +	struct string_list_item *item;
> +	struct string_list remotes = STRING_LIST_INIT_DUP;
> +
> +	if (for_each_remote(append_remote, &remotes)) {
> +		error(_("failed to fill remotes"));
> +		result = 1;
> +		goto cleanup;
> +	}
> +
> +	for_each_string_list_item(item, &remotes)
> +		result |= fetch_remote(item->string, opts);
> +
> +cleanup:
> +	string_list_clear(&remotes, 0);
> +	return result;
> +}

I was wondering why the generation of the list and the iteration was
split up, but I see that you want to attempt to fetch each remote even
if one of them fails.

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 2/8] maintenance: add loose-objects task
  2020-08-25 18:36     ` [PATCH v3 2/8] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
@ 2020-09-22 23:09       ` Jonathan Tan
  2020-09-24 13:45         ` Derrick Stolee
  0 siblings, 1 reply; 66+ messages in thread
From: Jonathan Tan @ 2020-09-22 23:09 UTC (permalink / raw)
  To: gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, jonathantanmy,
	derrickstolee, dstolee

> Create a 'loose-objects' task for the 'git maintenance run' command.
> This helps clean up loose objects without disrupting concurrent Git
> commands using the following sequence of events:
> 
> 1. Run 'git prune-packed' to delete any loose objects that exist
>    in a pack-file. Concurrent commands will prefer the packed
>    version of the object to the loose version. (Of course, there
>    are exceptions for commands that specifically care about the
>    location of an object. These are rare for a user to run on
>    purpose, and we hope a user that has selected background
>    maintenance will not be trying to do foreground maintenance.)
> 
> 2. Run 'git pack-objects' on a batch of loose objects. These
>    objects are grouped by scanning the loose object directories in
>    lexicographic order until listing all loose objects -or-
>    reaching 50,000 objects. This is more than enough if the loose
>    objects are created only by a user doing normal development.
>    We noticed users with _millions_ of loose objects because VFS
>    for Git downloads blobs on-demand when a file read operation
>    requires populating a virtual file. 

[snip]

> This has potential of
>    happening in partial clones if someone runs 'git grep' or
>    otherwise evades the batch-download feature for requesting
>    promisor objects.

This part is not strictly true, as even when Git lazy-fetches one
object, it fetches it in the form of a packfile - so maybe remove this
sentence.

This is nevertheless a good feature to have - loose objects may not be
created during lazy fetches, but they definitely are created during
normal operation (e.g. commits). Git, as a whole, prefers packfiles over
loose objects, and just packing the loose objects themselves instead of
running repack (which goes through all reachable objects) is definitely
better for large repositories.

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 3/8] maintenance: create auto condition for loose-objects
  2020-08-25 18:36     ` [PATCH v3 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
@ 2020-09-22 23:15       ` Jonathan Tan
  2020-09-24 13:51         ` Derrick Stolee
  0 siblings, 1 reply; 66+ messages in thread
From: Jonathan Tan @ 2020-09-22 23:15 UTC (permalink / raw)
  To: gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, jonathantanmy,
	derrickstolee, dstolee

> +test_expect_success 'maintenance.loose-objects.auto' '
> +	git repack -adk &&
> +	GIT_TRACE2_EVENT="$(pwd)/trace-lo1.txt" \
> +		git -c maintenance.loose-objects.auto=1 maintenance \
> +		run --auto --task=loose-objects 2>/dev/null &&
> +	test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
> +	for i in 1 2

Any reason why this is run twice?

> +	do
> +		printf data-A-$i | git hash-object -t blob --stdin -w &&
> +		GIT_TRACE2_EVENT="$(pwd)/trace-loA-$i" \
> +			git -c maintenance.loose-objects.auto=2 \
> +			maintenance run --auto --task=loose-objects 2>/dev/null &&
> +		test_subcommand ! git prune-packed --quiet <trace-loA-$i &&

OK - there is only 1 loose object so the loose-objects task doesn't
get run.

> +		printf data-B-$i | git hash-object -t blob --stdin -w &&
> +		GIT_TRACE2_EVENT="$(pwd)/trace-loB-$i" \
> +			git -c maintenance.loose-objects.auto=2 \
> +			maintenance run --auto --task=loose-objects 2>/dev/null &&
> +		test_subcommand git prune-packed --quiet <trace-loB-$i &&

OK - there are 2 loose objects so the loose-objects task gets run. But
we need to remember that the first time it is run, only the packfile
gets created - the loose objects aren't deleted. "prune-packed" here is
to show that the loose-objects task is run, but it has no effect.

> +		GIT_TRACE2_EVENT="$(pwd)/trace-loC-$i" \
> +			git -c maintenance.loose-objects.auto=2 \
> +			maintenance run --auto --task=loose-objects 2>/dev/null &&
> +		test_subcommand git prune-packed --quiet <trace-loC-$i || return 1

OK - the 2 loose objects still exist, so the loose-objects task gets
run. "prune-packed" here shows that the loose-objects task is run.

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 4/8] midx: enable core.multiPackIndex by default
  2020-08-25 18:36     ` [PATCH v3 4/8] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
@ 2020-09-22 23:16       ` Jonathan Tan
  2020-09-24 13:53         ` Derrick Stolee
  0 siblings, 1 reply; 66+ messages in thread
From: Jonathan Tan @ 2020-09-22 23:16 UTC (permalink / raw)
  To: gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, jonathantanmy,
	derrickstolee, dstolee

> diff --git a/repository.h b/repository.h
> index 3c1f7d54bd..3901ce0b65 100644
> --- a/repository.h
> +++ b/repository.h
> @@ -37,6 +37,8 @@ struct repo_settings {
>  
>  	int pack_use_sparse;
>  	enum fetch_negotiation_setting fetch_negotiation_algorithm;
> +
> +	int core_multi_pack_index;

The only thing I noticed here is why this isn't a bit ("unsigned
core_multi_pack_index : 1"), but I guess it is consistent with "int
pack_use_sparse".

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 6/8] maintenance: add incremental-repack task
  2020-08-25 18:36     ` [PATCH v3 6/8] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
@ 2020-09-22 23:26       ` Jonathan Tan
  2020-09-24 14:05         ` Derrick Stolee
  0 siblings, 1 reply; 66+ messages in thread
From: Jonathan Tan @ 2020-09-22 23:26 UTC (permalink / raw)
  To: gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, jonathantanmy,
	derrickstolee, dstolee

> +incremental-repack::
> +	The `incremental-repack` job repacks the object directory
> +	using the `multi-pack-index` feature. In order to prevent race
> +	conditions with concurrent Git commands, it follows a two-step
> +	process.

[snip]

> First, it deletes any pack-files included in the
> +	`multi-pack-index` where none of the objects in the
> +	`multi-pack-index` reference those pack-files; this only happens
> +	if all objects in the pack-file are also stored in a newer
> +	pack-file. Second, it selects a group of pack-files whose "expected
> +	size" is below the batch size until the group has total expected
> +	size at least the batch size; see the `--batch-size` option for
> +	the `repack` subcommand in linkgit:git-multi-pack-index[1]. The
> +	default batch-size is zero, which is a special case that attempts
> +	to repack all pack-files into a single pack-file.

This lacks the detail of what happens to the selected group of packfiles
(in the second step) - in particular, that a new packfile is created and
the MIDX is rewritten so that all references to the selected group are
updated to refer to the new packfile instead, thus making it possible to
delete the selected group of packfiles in a subsequent first step. All
this is explained in the documentation of git-multi-pack-index (expire
and repack), though, so it might be better to refer to that. E.g.

  First, it calls `multi-pack-index expire` to delete packfiles
  unreferenced by the MIDX file. Second, it calls `multi-pack-index
  repack` to select several small packfiles and repack them into a
  bigger one, and then update the MIDX entries that refer to the small
  packfiles to refer to the big one instead, thus preparing it for
  deletion upon a subsequent `multi-pack-index expire` invocation. The
  selection of the small packfiles is such that the expected size of the
  big packfile is at least the batch size; see the ...

> diff --git a/midx.c b/midx.c
> index aa37d5da86..66d7053d83 100644
> --- a/midx.c
> +++ b/midx.c
> @@ -37,7 +37,7 @@
>  
>  #define PACK_EXPIRED UINT_MAX
>  
> -static char *get_midx_filename(const char *object_dir)
> +char *get_midx_filename(const char *object_dir)
>  {
>  	return xstrfmt("%s/pack/multi-pack-index", object_dir);
>  }
> diff --git a/midx.h b/midx.h
> index b18cf53bc4..baeecc70c9 100644
> --- a/midx.h
> +++ b/midx.h
> @@ -37,6 +37,7 @@ struct multi_pack_index {
>  
>  #define MIDX_PROGRESS     (1 << 0)
>  
> +char *get_midx_filename(const char *object_dir);
>  struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local);
>  int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
>  int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result);

Do we need get_midx_filename() to be global?

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 8/8] maintenance: add incremental-repack auto condition
  2020-08-25 18:36     ` [PATCH v3 8/8] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
@ 2020-09-22 23:52       ` Jonathan Tan
  0 siblings, 0 replies; 66+ messages in thread
From: Jonathan Tan @ 2020-09-22 23:52 UTC (permalink / raw)
  To: gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, jonathantanmy,
	derrickstolee, dstolee

> diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
> index 5c08afc19a..6f878b0141 100755
> --- a/t/t7900-maintenance.sh
> +++ b/t/t7900-maintenance.sh
> @@ -220,4 +220,35 @@ test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
>  		 --no-progress --batch-size=2147483647 <run-2g.txt
>  '
>  
> +test_expect_success 'maintenance.incremental-repack.auto' '
> +	git repack -adk &&
> +	git config core.multiPackIndex true &&
> +	git multi-pack-index write &&

After this, there is exactly one pack, and it is in the MIDX.

> +	GIT_TRACE2_EVENT="$(pwd)/midx-init.txt" git \
> +		-c maintenance.incremental-repack.auto=1 \
> +		maintenance run --auto --task=incremental-repack 2>/dev/null &&
> +	test_subcommand ! git multi-pack-index write --no-progress <midx-init.txt &&
> +	for i in 1 2

Same comment as in the earlier patch - why 2 iterations?

> +	do
> +		test_commit A-$i &&
> +		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
> +		HEAD
> +		^HEAD~1
> +		EOF
> +		GIT_TRACE2_EVENT=$(pwd)/trace-A-$i git \
> +			-c maintenance.incremental-repack.auto=2 \
> +			maintenance run --auto --task=incremental-repack 2>/dev/null &&
> +		test_subcommand ! git multi-pack-index write --no-progress <trace-A-$i &&

OK - one pack not in the MIDX, so this does not get run.

> +		test_commit B-$i &&
> +		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
> +		HEAD
> +		^HEAD~1
> +		EOF
> +		GIT_TRACE2_EVENT=$(pwd)/trace-B-$i git \
> +			-c maintenance.incremental-repack.auto=2 \
> +			maintenance run --auto --task=incremental-repack 2>/dev/null &&
> +		test_subcommand git multi-pack-index write --no-progress <trace-B-$i || return 1

OK - 2 packs not in the MIDX, so this gets run.

As I said in my review of patch 1, apart from my minor comments in this
and the preceding patches, these patches look good to me.

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 2/8] maintenance: add loose-objects task
  2020-09-22 23:09       ` Jonathan Tan
@ 2020-09-24 13:45         ` Derrick Stolee
  0 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee @ 2020-09-24 13:45 UTC (permalink / raw)
  To: Jonathan Tan, gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, derrickstolee, dstolee

On 9/22/2020 7:09 PM, Jonathan Tan wrote:
>> Create a 'loose-objects' task for the 'git maintenance run' command.
>> This helps clean up loose objects without disrupting concurrent Git
>> commands using the following sequence of events:
>>
>> 1. Run 'git prune-packed' to delete any loose objects that exist
>>    in a pack-file. Concurrent commands will prefer the packed
>>    version of the object to the loose version. (Of course, there
>>    are exceptions for commands that specifically care about the
>>    location of an object. These are rare for a user to run on
>>    purpose, and we hope a user that has selected background
>>    maintenance will not be trying to do foreground maintenance.)
>>
>> 2. Run 'git pack-objects' on a batch of loose objects. These
>>    objects are grouped by scanning the loose object directories in
>>    lexicographic order until listing all loose objects -or-
>>    reaching 50,000 objects. This is more than enough if the loose
>>    objects are created only by a user doing normal development.
>>    We noticed users with _millions_ of loose objects because VFS
>>    for Git downloads blobs on-demand when a file read operation
>>    requires populating a virtual file. 
> 
> [snip]
> 
>> This has potential of
>>    happening in partial clones if someone runs 'git grep' or
>>    otherwise evades the batch-download feature for requesting
>>    promisor objects.
> 
> This part is not strictly true, as even when Git lazy-fetches one
> object, it fetches it in the form of a packfile - so maybe remove this
> sentence.

This is a good point. I just did some testing and we do store these
single-object downloads as pack-files. My misunderstanding is due to
my own bias and experience with the GVFS protocol.

I have also heard that "git fetch" might explode some small pack-files
into loose objects, and I guess I expected the same here. However, that
is not the case for partial clone. I'll remove this.

> This is nevertheless a good feature to have - loose objects may not be
> created during lazy fetches, but they definitely are created during
> normal operation (e.g. commits). Git, as a whole, prefers packfiles over
> loose objects, and just packing the loose objects themselves instead of
> running repack (which goes through all reachable objects) is definitely
> better for large repositories.

Thanks,
-Stolee


^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 3/8] maintenance: create auto condition for loose-objects
  2020-09-22 23:15       ` Jonathan Tan
@ 2020-09-24 13:51         ` Derrick Stolee
  0 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee @ 2020-09-24 13:51 UTC (permalink / raw)
  To: Jonathan Tan, gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, derrickstolee, dstolee

On 9/22/2020 7:15 PM, Jonathan Tan wrote:
>> +test_expect_success 'maintenance.loose-objects.auto' '
>> +	git repack -adk &&
>> +	GIT_TRACE2_EVENT="$(pwd)/trace-lo1.txt" \
>> +		git -c maintenance.loose-objects.auto=1 maintenance \
>> +		run --auto --task=loose-objects 2>/dev/null &&
>> +	test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
>> +	for i in 1 2
> 
> Any reason why this is run twice?

I think the original reason was to demonstrate how two runs interact,
but then that was done in the middle of the loop body so the loop is
not necessary.

Thanks,
-Stolee


^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 4/8] midx: enable core.multiPackIndex by default
  2020-09-22 23:16       ` Jonathan Tan
@ 2020-09-24 13:53         ` Derrick Stolee
  0 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee @ 2020-09-24 13:53 UTC (permalink / raw)
  To: Jonathan Tan, gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, derrickstolee, dstolee

On 9/22/2020 7:16 PM, Jonathan Tan wrote:
>> diff --git a/repository.h b/repository.h
>> index 3c1f7d54bd..3901ce0b65 100644
>> --- a/repository.h
>> +++ b/repository.h
>> @@ -37,6 +37,8 @@ struct repo_settings {
>>  
>>  	int pack_use_sparse;
>>  	enum fetch_negotiation_setting fetch_negotiation_algorithm;
>> +
>> +	int core_multi_pack_index;
> 
> The only thing I noticed here is why this isn't a bit ("unsigned
> core_multi_pack_index : 1"), but I guess it is consistent with "int
> pack_use_sparse".

The _real_ reason is that we initialize these to -1 in
prepare_repo_settings() so UPDATE_DEFAULT_BOOL() knows that
the setting was not populated by a config value.

Thanks,
-Stolee


^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 6/8] maintenance: add incremental-repack task
  2020-09-22 23:26       ` Jonathan Tan
@ 2020-09-24 14:05         ` Derrick Stolee
  2020-09-24 22:01           ` Jonathan Tan
  0 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee @ 2020-09-24 14:05 UTC (permalink / raw)
  To: Jonathan Tan, gitgitgadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, derrickstolee, dstolee

On 9/22/2020 7:26 PM, Jonathan Tan wrote:
>> +incremental-repack::
>> +	The `incremental-repack` job repacks the object directory
>> +	using the `multi-pack-index` feature. In order to prevent race
>> +	conditions with concurrent Git commands, it follows a two-step
>> +	process.
> 
> [snip]
> 
>> First, it deletes any pack-files included in the
>> +	`multi-pack-index` where none of the objects in the
>> +	`multi-pack-index` reference those pack-files; this only happens
>> +	if all objects in the pack-file are also stored in a newer
>> +	pack-file. Second, it selects a group of pack-files whose "expected
>> +	size" is below the batch size until the group has total expected
>> +	size at least the batch size; see the `--batch-size` option for
>> +	the `repack` subcommand in linkgit:git-multi-pack-index[1]. The
>> +	default batch-size is zero, which is a special case that attempts
>> +	to repack all pack-files into a single pack-file.
> 
> This lacks the detail of what happens to the selected group of packfiles
> (in the second step) - in particular, that a new packfile is created and
> the MIDX is rewritten so that all references to the selected group are
> updated to refer to the new packfile instead, thus making it possible to
> delete the selected group of packfiles in a subsequent first step. All
> this is explained in the documentation of git-multi-pack-index (expire
> and repack), though, so it might be better to refer to that. E.g.

Here is my attempt to incorporate your recommendations into this doc:

incremental-repack::
	The `incremental-repack` job repacks the object directory
	using the `multi-pack-index` feature. In order to prevent race
	conditions with concurrent Git commands, it follows a two-step
	process. First, it calls `git multi-pack-index expire` to delete
	pack-files unreferenced by the `multi-pack-index` file. Second, it
	calls `git multi-pack-index repack` to select several small
	pack-files and repack them into a bigger one, and then update the
	`multi-pack-index` entries that refer to the small pack-files to
	refer to the new pack-file. This prepares those small pack-files
	for deletion upon the next run of `git multi-pack-index expire`.
	The selection of the small pack-files is such that the expected
	size of the big pack-file is at least the batch size; see the
	`--batch-size` option for the `repack` subcommand in
	linkgit:git-multi-pack-index[1]. The default batch-size is zero,
	which is a special case that attempts to repack all pack-files
	into a single pack-file.

> Do we need get_midx_filename() to be global?

No, that does not appear to be important (to this patch). It _was_
necessary when doing the "verify, then delete if problematic" mode.
Thanks for catching it now that it is not necessary.

Thanks,
-Stolee
 


^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v3 6/8] maintenance: add incremental-repack task
  2020-09-24 14:05         ` Derrick Stolee
@ 2020-09-24 22:01           ` Jonathan Tan
  0 siblings, 0 replies; 66+ messages in thread
From: Jonathan Tan @ 2020-09-24 22:01 UTC (permalink / raw)
  To: stolee
  Cc: jonathantanmy, gitgitgadget, git, sandals, steadmon, jrnieder,
	peff, congdanhqx, phillip.wood123, emilyshaffer, sluongng,
	derrickstolee, dstolee

> Here is my attempt to incorporate your recommendations into this doc:
> 
> incremental-repack::
> 	The `incremental-repack` job repacks the object directory
> 	using the `multi-pack-index` feature. In order to prevent race
> 	conditions with concurrent Git commands, it follows a two-step
> 	process. First, it calls `git multi-pack-index expire` to delete
> 	pack-files unreferenced by the `multi-pack-index` file. Second, it
> 	calls `git multi-pack-index repack` to select several small
> 	pack-files and repack them into a bigger one, and then update the
> 	`multi-pack-index` entries that refer to the small pack-files to
> 	refer to the new pack-file. This prepares those small pack-files
> 	for deletion upon the next run of `git multi-pack-index expire`.
> 	The selection of the small pack-files is such that the expected
> 	size of the big pack-file is at least the batch size; see the
> 	`--batch-size` option for the `repack` subcommand in
> 	linkgit:git-multi-pack-index[1]. The default batch-size is zero,
> 	which is a special case that attempts to repack all pack-files
> 	into a single pack-file.

Thanks, this looks good.

^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v4 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks
  2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
                       ` (9 preceding siblings ...)
  2020-08-26 15:15     ` Son Luong Ngoc
@ 2020-09-25 12:33     ` Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
                         ` (7 more replies)
  10 siblings, 8 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-09-25 12:33 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Jonathan Tan,
	Derrick Stolee, Derrick Stolee

This series is based on ds/maintenance-part-1 [2].

This patch series contains 9 patches that were going to be part of v4 of
ds/maintenance [1], but the discussion has gotten really long. To help, I'm
splitting out the portions that create and test the 'maintenance' builtin
from the additional tasks (prefetch, loose-objects, incremental-repack) that
can be brought in later.

[1] 
https://lore.kernel.org/git/pull.671.git.1594131695.gitgitgadget@gmail.com/
[2] 
https://lore.kernel.org/git/pull.695.v3.git.1598380426.gitgitgadget@gmail.com/

As detailed in [2], the 'git maintenance run' subcommand will run certain
tasks based on config options or the --task= arguments. The --auto option
indicates to the task to only run based on some internal check that there
has been "enough" change in that domain to merit the work. In the case of
the 'gc' task, this also reduces the amount of work done. 

The new maintenance tasks in this series are:

 * 'loose-objects' : prune packed loose objects, then create a new pack from
   a batch of loose objects.
 * 'pack-files' : expire redundant packs from the multi-pack-index, then
   repack using the multi-pack-index's incremental repack strategy.
 * 'prefetch' : fetch from each remote, storing the refs in 'refs/prefetch/
   /'.

These tasks are all disabled by default, but can be enabled with config
options or run explicitly using "git maintenance run --task=". 

Since [2] replaced the 'git gc --auto' calls with 'git maintenance run
--auto' at the end of some Git commands, users could replace the 'gc' task
with these lighter-weight changes for foreground maintenance.

The 'git maintenance' builtin has a 'run' subcommand so it can be extended
later with subcommands that manage background maintenance, such as 'start'
or 'stop'. These are not the subject of this series, as it is important to
focus on the maintenance activities themselves. I have an RFC series for
this available at [3].

[3] 
https://lore.kernel.org/git/pull.680.git.1597857408.gitgitgadget@gmail.com/

Updates in v3
=============

 * Several commit message, documentation, and test updates from Jonathan
   Tan's helpful review!

Updates since v2
================

 * Dropped "fetch: optionally allow disabling FETCH_HEAD update"
   
   
 * A lot of fallout from the change in the option parsing in v3 of
   Maintenance II.
   
   
 * Dropped the "verify, and delete and rewrite on failure" logic from the
   incremental-repack task. This might be added again later after it can be
   tested more thoroughly.
   
   

Updates since v1 (of this series)
=================================

 * PATCH 1 ("fetch: optionally allow disabling FETCH_HEAD update") was
   rewritten on-list. Getting a version out with this patch is the main
   reason for rolling a v2. (That, and Part I is re-rolled with a v2 and I
   want to make sure this series applies cleanly.)
   
   
 * The 'prefetch' and 'loose-objects' tasks had some review, but my proposed
   changes were not acked, so they may need another review.
   
   

UPDATES since v3 of [1]
=======================

 * The biggest change here is the use of "test_subcommand", based on
   Jonathan Nieder's approach. This requires having the exact command-line
   figured out, which now requires spelling out all --no- [quiet%7Cprogress] 
   options. I also added a bunch of "2>/dev/null" checks because of the
   isatty(2) calls. Without that, the behavior will change depending on
   whether the test is run with -x/-v or without.
   
   
 * The 0x7FFF/0x7FFFFFFF constant problem is fixed with an EXPENSIVE test
   that verifies it.
   
   
 * The option parsing has changed to use a local struct and pass that struct
   to the helper methods. This is instead of having a global singleton.
   
   

Thanks, -Stolee

Derrick Stolee (8):
  maintenance: add prefetch task
  maintenance: add loose-objects task
  maintenance: create auto condition for loose-objects
  midx: enable core.multiPackIndex by default
  midx: use start_delayed_progress()
  maintenance: add incremental-repack task
  maintenance: auto-size incremental-repack batch
  maintenance: add incremental-repack auto condition

 Documentation/config/core.txt        |   4 +-
 Documentation/config/maintenance.txt |  18 ++
 Documentation/git-maintenance.txt    |  48 ++++
 builtin/gc.c                         | 326 +++++++++++++++++++++++++++
 midx.c                               |  21 +-
 repo-settings.c                      |   6 +
 repository.h                         |   2 +
 t/t5319-multi-pack-index.sh          |  15 +-
 t/t7900-maintenance.sh               | 185 +++++++++++++++
 9 files changed, 603 insertions(+), 22 deletions(-)


base-commit: 25914c4fdeefd99b06e134496dfb9bbb58a5c417
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-696%2Fderrickstolee%2Fmaintenance%2Fgc-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-696/derrickstolee/maintenance/gc-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/696

Range-diff vs v3:

 1:  da64c51a81 ! 1:  7a62e224cf maintenance: add prefetch task
     @@ Commit message
          of a foreground fetch to make that 'git fetch' command much faster.
      
          However, if we simply ran 'git fetch <remote>' in the background,
     -    then the user running a foregroudn 'git fetch <remote>' would lose
     +    then the user running a foreground 'git fetch <remote>' would lose
          some important feedback when a new branch appears or an existing
          branch updates. This is especially true if a remote branch is
          force-updated and this isn't noticed by the user because it occurred
 2:  75e846456b ! 2:  f3a16fd324 maintenance: add loose-objects task
     @@ Commit message
             objects are created only by a user doing normal development.
             We noticed users with _millions_ of loose objects because VFS
             for Git downloads blobs on-demand when a file read operation
     -       requires populating a virtual file. This has potential of
     -       happening in partial clones if someone runs 'git grep' or
     -       otherwise evades the batch-download feature for requesting
     -       promisor objects.
     +       requires populating a virtual file.
      
          This step is based on a similar step in Scalar [1] and VFS for Git.
          [1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/LooseObjectsStep.cs
 3:  d6e382c43e ! 3:  931fff4883 maintenance: create auto condition for loose-objects
     @@ t/t7900-maintenance.sh: test_expect_success 'loose-objects task' '
      +		git -c maintenance.loose-objects.auto=1 maintenance \
      +		run --auto --task=loose-objects 2>/dev/null &&
      +	test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
     -+	for i in 1 2
     -+	do
     -+		printf data-A-$i | git hash-object -t blob --stdin -w &&
     -+		GIT_TRACE2_EVENT="$(pwd)/trace-loA-$i" \
     -+			git -c maintenance.loose-objects.auto=2 \
     -+			maintenance run --auto --task=loose-objects 2>/dev/null &&
     -+		test_subcommand ! git prune-packed --quiet <trace-loA-$i &&
     -+		printf data-B-$i | git hash-object -t blob --stdin -w &&
     -+		GIT_TRACE2_EVENT="$(pwd)/trace-loB-$i" \
     -+			git -c maintenance.loose-objects.auto=2 \
     -+			maintenance run --auto --task=loose-objects 2>/dev/null &&
     -+		test_subcommand git prune-packed --quiet <trace-loB-$i &&
     -+		GIT_TRACE2_EVENT="$(pwd)/trace-loC-$i" \
     -+			git -c maintenance.loose-objects.auto=2 \
     -+			maintenance run --auto --task=loose-objects 2>/dev/null &&
     -+		test_subcommand git prune-packed --quiet <trace-loC-$i || return 1
     -+	done
     ++	printf data-A | git hash-object -t blob --stdin -w &&
     ++	GIT_TRACE2_EVENT="$(pwd)/trace-loA" \
     ++		git -c maintenance.loose-objects.auto=2 \
     ++		maintenance run --auto --task=loose-objects 2>/dev/null &&
     ++	test_subcommand ! git prune-packed --quiet <trace-loA &&
     ++	printf data-B | git hash-object -t blob --stdin -w &&
     ++	GIT_TRACE2_EVENT="$(pwd)/trace-loB" \
     ++		git -c maintenance.loose-objects.auto=2 \
     ++		maintenance run --auto --task=loose-objects 2>/dev/null &&
     ++	test_subcommand git prune-packed --quiet <trace-loB &&
     ++	GIT_TRACE2_EVENT="$(pwd)/trace-loC" \
     ++		git -c maintenance.loose-objects.auto=2 \
     ++		maintenance run --auto --task=loose-objects 2>/dev/null &&
     ++	test_subcommand git prune-packed --quiet <trace-loC
      +'
      +
       test_done
 4:  d0f2ec70d9 = 4:  0fe2036aa8 midx: enable core.multiPackIndex by default
 5:  2cd3c803d9 = 5:  ce435bf784 midx: use start_delayed_progress()
 6:  0dd26bb584 ! 6:  d934899253 maintenance: add incremental-repack task
     @@ Documentation/git-maintenance.txt: loose-objects::
      +	The `incremental-repack` job repacks the object directory
      +	using the `multi-pack-index` feature. In order to prevent race
      +	conditions with concurrent Git commands, it follows a two-step
     -+	process. First, it deletes any pack-files included in the
     -+	`multi-pack-index` where none of the objects in the
     -+	`multi-pack-index` reference those pack-files; this only happens
     -+	if all objects in the pack-file are also stored in a newer
     -+	pack-file. Second, it selects a group of pack-files whose "expected
     -+	size" is below the batch size until the group has total expected
     -+	size at least the batch size; see the `--batch-size` option for
     -+	the `repack` subcommand in linkgit:git-multi-pack-index[1]. The
     -+	default batch-size is zero, which is a special case that attempts
     -+	to repack all pack-files into a single pack-file.
     ++	process. First, it calls `git multi-pack-index expire` to delete
     ++	pack-files unreferenced by the `multi-pack-index` file. Second, it
     ++	calls `git multi-pack-index repack` to select several small
     ++	pack-files and repack them into a bigger one, and then update the
     ++	`multi-pack-index` entries that refer to the small pack-files to
     ++	refer to the new pack-file. This prepares those small pack-files
     ++	for deletion upon the next run of `git multi-pack-index expire`.
     ++	The selection of the small pack-files is such that the expected
     ++	size of the big pack-file is at least the batch size; see the
     ++	`--batch-size` option for the `repack` subcommand in
     ++	linkgit:git-multi-pack-index[1]. The default batch-size is zero,
     ++	which is a special case that attempts to repack all pack-files
     ++	into a single pack-file.
      +
       OPTIONS
       -------
       --auto::
      
       ## builtin/gc.c ##
     -@@
     - #include "promisor-remote.h"
     - #include "refs.h"
     - #include "remote.h"
     -+#include "midx.h"
     - 
     - #define FAILED_RUN "failed to run %s"
     - 
      @@ builtin/gc.c: static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
       	return prune_packed(opts) || pack_loose(opts);
       }
     @@ builtin/gc.c: static struct maintenance_task tasks[] = {
       		"gc",
       		maintenance_task_gc,
      
     - ## midx.c ##
     -@@
     - 
     - #define PACK_EXPIRED UINT_MAX
     - 
     --static char *get_midx_filename(const char *object_dir)
     -+char *get_midx_filename(const char *object_dir)
     - {
     - 	return xstrfmt("%s/pack/multi-pack-index", object_dir);
     - }
     -
     - ## midx.h ##
     -@@ midx.h: struct multi_pack_index {
     - 
     - #define MIDX_PROGRESS     (1 << 0)
     - 
     -+char *get_midx_filename(const char *object_dir);
     - struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local);
     - int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
     - int bsearch_midx(const struct object_id *oid, struct multi_pack_index *m, uint32_t *result);
     -
       ## t/t5319-multi-pack-index.sh ##
      @@
       test_description='multi-pack-indexes'
     @@ t/t7900-maintenance.sh: test_description='git maintenance builtin'
       test_expect_success 'help text' '
       	test_expect_code 129 git maintenance -h 2>err &&
      @@ t/t7900-maintenance.sh: test_expect_success 'maintenance.loose-objects.auto' '
     - 	done
     + 	test_subcommand git prune-packed --quiet <trace-loC
       '
       
      +test_expect_success 'incremental-repack task' '
 7:  f3b25a9927 = 7:  bade7706d5 maintenance: auto-size incremental-repack batch
 8:  e9bb32f53a ! 8:  f660dd1890 maintenance: add incremental-repack auto condition
     @@ Documentation/config/maintenance.txt: maintenance.loose-objects.auto::
      
       ## builtin/gc.c ##
      @@
     + #include "promisor-remote.h"
       #include "refs.h"
       #include "remote.h"
     - #include "midx.h"
      +#include "object-store.h"
       
       #define FAILED_RUN "failed to run %s"
     @@ t/t7900-maintenance.sh: test_expect_success EXPENSIVE 'incremental-repack 2g lim
      +		-c maintenance.incremental-repack.auto=1 \
      +		maintenance run --auto --task=incremental-repack 2>/dev/null &&
      +	test_subcommand ! git multi-pack-index write --no-progress <midx-init.txt &&
     -+	for i in 1 2
     -+	do
     -+		test_commit A-$i &&
     -+		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
     -+		HEAD
     -+		^HEAD~1
     -+		EOF
     -+		GIT_TRACE2_EVENT=$(pwd)/trace-A-$i git \
     -+			-c maintenance.incremental-repack.auto=2 \
     -+			maintenance run --auto --task=incremental-repack 2>/dev/null &&
     -+		test_subcommand ! git multi-pack-index write --no-progress <trace-A-$i &&
     -+		test_commit B-$i &&
     -+		git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
     -+		HEAD
     -+		^HEAD~1
     -+		EOF
     -+		GIT_TRACE2_EVENT=$(pwd)/trace-B-$i git \
     -+			-c maintenance.incremental-repack.auto=2 \
     -+			maintenance run --auto --task=incremental-repack 2>/dev/null &&
     -+		test_subcommand git multi-pack-index write --no-progress <trace-B-$i || return 1
     -+	done
     ++	test_commit A &&
     ++	git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
     ++	HEAD
     ++	^HEAD~1
     ++	EOF
     ++	GIT_TRACE2_EVENT=$(pwd)/trace-A git \
     ++		-c maintenance.incremental-repack.auto=2 \
     ++		maintenance run --auto --task=incremental-repack 2>/dev/null &&
     ++	test_subcommand ! git multi-pack-index write --no-progress <trace-A &&
     ++	test_commit B &&
     ++	git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
     ++	HEAD
     ++	^HEAD~1
     ++	EOF
     ++	GIT_TRACE2_EVENT=$(pwd)/trace-B git \
     ++		-c maintenance.incremental-repack.auto=2 \
     ++		maintenance run --auto --task=incremental-repack 2>/dev/null &&
     ++	test_subcommand git multi-pack-index write --no-progress <trace-B
      +'
      +
       test_done

-- 
gitgitgadget

^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v4 1/8] maintenance: add prefetch task
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
@ 2020-09-25 12:33       ` Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 2/8] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
                         ` (6 subsequent siblings)
  7 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-09-25 12:33 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Jonathan Tan,
	Derrick Stolee, Derrick Stolee, Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

When working with very large repositories, an incremental 'git fetch'
command can download a large amount of data. If there are many other
users pushing to a common repo, then this data can rival the initial
pack-file size of a 'git clone' of a medium-size repo.

Users may want to keep the data on their local repos as close as
possible to the data on the remote repos by fetching periodically in
the background. This can break up a large daily fetch into several
smaller hourly fetches.

The task is called "prefetch" because it is work done in advance
of a foreground fetch to make that 'git fetch' command much faster.

However, if we simply ran 'git fetch <remote>' in the background,
then the user running a foreground 'git fetch <remote>' would lose
some important feedback when a new branch appears or an existing
branch updates. This is especially true if a remote branch is
force-updated and this isn't noticed by the user because it occurred
in the background. Further, the functionality of 'git push
--force-with-lease' becomes suspect.

When running 'git fetch <remote> <options>' in the background, use
the following options for careful updating:

1. --no-tags prevents getting a new tag when a user wants to see
   the new tags appear in their foreground fetches.

2. --refmap= removes the configured refspec which usually updates
   refs/remotes/<remote>/* with the refs advertised by the remote.
   While this looks confusing, this was documented and tested by
   b40a50264ac (fetch: document and test --refmap="", 2020-01-21),
   including this sentence in the documentation:

	Providing an empty `<refspec>` to the `--refmap` option
	causes Git to ignore the configured refspecs and rely
	entirely on the refspecs supplied as command-line arguments.

3. By adding a new refspec "+refs/heads/*:refs/prefetch/<remote>/*"
   we can ensure that we actually load the new values somewhere in
   our refspace while not updating refs/heads or refs/remotes. By
   storing these refs here, the commit-graph job will update the
   commit-graph with the commits from these hidden refs.

4. --prune will delete the refs/prefetch/<remote> refs that no
   longer appear on the remote.

5. --no-write-fetch-head prevents updating FETCH_HEAD.

We've been using this step as a critical background job in Scalar
[1] (and VFS for Git). This solved a pain point that was showing up
in user reports: fetching was a pain! Users do not like waiting to
download the data that was created while they were away from their
machines. After implementing background fetch, the foreground fetch
commands sped up significantly because they mostly just update refs
and download a small amount of new data. The effect is especially
dramatic when paried with --no-show-forced-udpates (through
fetch.showForcedUpdates=false).

[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/FetchStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 15 +++++++++
 builtin/gc.c                      | 51 +++++++++++++++++++++++++++++++
 t/t7900-maintenance.sh            | 26 ++++++++++++++++
 3 files changed, 92 insertions(+)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 6abcb8255a..12668fccf7 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -47,6 +47,21 @@ commit-graph::
 	`commit-graph-chain` file. They will be deleted by a later run based
 	on the expiration delay.
 
+prefetch::
+	The `prefetch` task updates the object directory with the latest
+	objects from all registered remotes. For each remote, a `git fetch`
+	command is run. The refmap is custom to avoid updating local or remote
+	branches (those in `refs/heads` or `refs/remotes`). Instead, the
+	remote refs are stored in `refs/prefetch/<remote>/`. Also, tags are
+	not updated.
++
+This is done to avoid disrupting the remote-tracking branches. The end users
+expect these refs to stay unmoved unless they initiate a fetch.  With prefetch
+task, however, the objects necessary to complete a later real fetch would
+already be obtained, so the real fetch would go faster.  In the ideal case,
+it will just become an update to bunch of remote-tracking branches without
+any object transfer.
+
 gc::
 	Clean up unnecessary files and optimize the local repository. "GC"
 	stands for "garbage collection," but this task performs many
diff --git a/builtin/gc.c b/builtin/gc.c
index 090959350e..5e469488f4 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -29,6 +29,7 @@
 #include "tree.h"
 #include "promisor-remote.h"
 #include "refs.h"
+#include "remote.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -816,6 +817,51 @@ static int maintenance_task_commit_graph(struct maintenance_run_opts *opts)
 	return 0;
 }
 
+static int fetch_remote(const char *remote, struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "fetch", remote, "--prune", "--no-tags",
+		     "--no-write-fetch-head", "--recurse-submodules=no",
+		     "--refmap=", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--quiet");
+
+	strvec_pushf(&child.args, "+refs/heads/*:refs/prefetch/%s/*", remote);
+
+	return !!run_command(&child);
+}
+
+static int append_remote(struct remote *remote, void *cbdata)
+{
+	struct string_list *remotes = (struct string_list *)cbdata;
+
+	string_list_append(remotes, remote->name);
+	return 0;
+}
+
+static int maintenance_task_prefetch(struct maintenance_run_opts *opts)
+{
+	int result = 0;
+	struct string_list_item *item;
+	struct string_list remotes = STRING_LIST_INIT_DUP;
+
+	if (for_each_remote(append_remote, &remotes)) {
+		error(_("failed to fill remotes"));
+		result = 1;
+		goto cleanup;
+	}
+
+	for_each_string_list_item(item, &remotes)
+		result |= fetch_remote(item->string, opts);
+
+cleanup:
+	string_list_clear(&remotes, 0);
+	return result;
+}
+
 static int maintenance_task_gc(struct maintenance_run_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -854,6 +900,7 @@ struct maintenance_task {
 };
 
 enum maintenance_task_label {
+	TASK_PREFETCH,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -862,6 +909,10 @@ enum maintenance_task_label {
 };
 
 static struct maintenance_task tasks[] = {
+	[TASK_PREFETCH] = {
+		"prefetch",
+		maintenance_task_prefetch,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 53c883531e..045524e6ad 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -62,4 +62,30 @@ test_expect_success 'run --task duplicate' '
 	test_i18ngrep "cannot be selected multiple times" err
 '
 
+test_expect_success 'run --task=prefetch with no remotes' '
+	git maintenance run --task=prefetch 2>err &&
+	test_must_be_empty err
+'
+
+test_expect_success 'prefetch multiple remotes' '
+	git clone . clone1 &&
+	git clone . clone2 &&
+	git remote add remote1 "file://$(pwd)/clone1" &&
+	git remote add remote2 "file://$(pwd)/clone2" &&
+	git -C clone1 switch -c one &&
+	git -C clone2 switch -c two &&
+	test_commit -C clone1 one &&
+	test_commit -C clone2 two &&
+	GIT_TRACE2_EVENT="$(pwd)/run-prefetch.txt" git maintenance run --task=prefetch 2>/dev/null &&
+	fetchargs="--prune --no-tags --no-write-fetch-head --recurse-submodules=no --refmap= --quiet" &&
+	test_subcommand git fetch remote1 $fetchargs +refs/heads/\\*:refs/prefetch/remote1/\\* <run-prefetch.txt &&
+	test_subcommand git fetch remote2 $fetchargs +refs/heads/\\*:refs/prefetch/remote2/\\* <run-prefetch.txt &&
+	test_path_is_missing .git/refs/remotes &&
+	git log prefetch/remote1/one &&
+	git log prefetch/remote2/two &&
+	git fetch --all &&
+	test_cmp_rev refs/remotes/remote1/one refs/prefetch/remote1/one &&
+	test_cmp_rev refs/remotes/remote2/two refs/prefetch/remote2/two
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v4 2/8] maintenance: add loose-objects task
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
@ 2020-09-25 12:33       ` Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
                         ` (5 subsequent siblings)
  7 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-09-25 12:33 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Jonathan Tan,
	Derrick Stolee, Derrick Stolee, Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

One goal of background maintenance jobs is to allow a user to
disable auto-gc (gc.auto=0) but keep their repository in a clean
state. Without any cleanup, loose objects will clutter the object
database and slow operations. In addition, the loose objects will
take up extra space because they are not stored with deltas against
similar objects.

Create a 'loose-objects' task for the 'git maintenance run' command.
This helps clean up loose objects without disrupting concurrent Git
commands using the following sequence of events:

1. Run 'git prune-packed' to delete any loose objects that exist
   in a pack-file. Concurrent commands will prefer the packed
   version of the object to the loose version. (Of course, there
   are exceptions for commands that specifically care about the
   location of an object. These are rare for a user to run on
   purpose, and we hope a user that has selected background
   maintenance will not be trying to do foreground maintenance.)

2. Run 'git pack-objects' on a batch of loose objects. These
   objects are grouped by scanning the loose object directories in
   lexicographic order until listing all loose objects -or-
   reaching 50,000 objects. This is more than enough if the loose
   objects are created only by a user doing normal development.
   We noticed users with _millions_ of loose objects because VFS
   for Git downloads blobs on-demand when a file read operation
   requires populating a virtual file.

This step is based on a similar step in Scalar [1] and VFS for Git.
[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/LooseObjectsStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 15 +++++
 builtin/gc.c                      | 97 +++++++++++++++++++++++++++++++
 t/t7900-maintenance.sh            | 39 +++++++++++++
 3 files changed, 151 insertions(+)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index 12668fccf7..fc95eb594f 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -70,6 +70,21 @@ gc::
 	be disruptive in some situations, as it deletes stale data. See
 	linkgit:git-gc[1] for more details on garbage collection in Git.
 
+loose-objects::
+	The `loose-objects` job cleans up loose objects and places them into
+	pack-files. In order to prevent race conditions with concurrent Git
+	commands, it follows a two-step process. First, it deletes any loose
+	objects that already exist in a pack-file; concurrent Git processes
+	will examine the pack-file for the object data instead of the loose
+	object. Second, it creates a new pack-file (starting with "loose-")
+	containing a batch of loose objects. The batch size is limited to 50
+	thousand objects to prevent the job from taking too long on a
+	repository with many loose objects. The `gc` task writes unreachable
+	objects as loose objects to be cleaned up by a later step only if
+	they are not re-added to a pack-file; for this reason it is not
+	advisable to enable both the `loose-objects` and `gc` tasks at the
+	same time.
+
 OPTIONS
 -------
 --auto::
diff --git a/builtin/gc.c b/builtin/gc.c
index 5e469488f4..c9db8555b9 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -880,6 +880,98 @@ static int maintenance_task_gc(struct maintenance_run_opts *opts)
 	return run_command(&child);
 }
 
+static int prune_packed(struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_push(&child.args, "prune-packed");
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--quiet");
+
+	return !!run_command(&child);
+}
+
+struct write_loose_object_data {
+	FILE *in;
+	int count;
+	int batch_size;
+};
+
+static int bail_on_loose(const struct object_id *oid,
+			 const char *path,
+			 void *data)
+{
+	return 1;
+}
+
+static int write_loose_object_to_stdin(const struct object_id *oid,
+				       const char *path,
+				       void *data)
+{
+	struct write_loose_object_data *d = (struct write_loose_object_data *)data;
+
+	fprintf(d->in, "%s\n", oid_to_hex(oid));
+
+	return ++(d->count) > d->batch_size;
+}
+
+static int pack_loose(struct maintenance_run_opts *opts)
+{
+	struct repository *r = the_repository;
+	int result = 0;
+	struct write_loose_object_data data;
+	struct child_process pack_proc = CHILD_PROCESS_INIT;
+
+	/*
+	 * Do not start pack-objects process
+	 * if there are no loose objects.
+	 */
+	if (!for_each_loose_file_in_objdir(r->objects->odb->path,
+					   bail_on_loose,
+					   NULL, NULL, NULL))
+		return 0;
+
+	pack_proc.git_cmd = 1;
+
+	strvec_push(&pack_proc.args, "pack-objects");
+	if (opts->quiet)
+		strvec_push(&pack_proc.args, "--quiet");
+	strvec_pushf(&pack_proc.args, "%s/pack/loose", r->objects->odb->path);
+
+	pack_proc.in = -1;
+
+	if (start_command(&pack_proc)) {
+		error(_("failed to start 'git pack-objects' process"));
+		return 1;
+	}
+
+	data.in = xfdopen(pack_proc.in, "w");
+	data.count = 0;
+	data.batch_size = 50000;
+
+	for_each_loose_file_in_objdir(r->objects->odb->path,
+				      write_loose_object_to_stdin,
+				      NULL,
+				      NULL,
+				      &data);
+
+	fclose(data.in);
+
+	if (finish_command(&pack_proc)) {
+		error(_("failed to finish 'git pack-objects' process"));
+		result = 1;
+	}
+
+	return result;
+}
+
+static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
+{
+	return prune_packed(opts) || pack_loose(opts);
+}
+
 typedef int maintenance_task_fn(struct maintenance_run_opts *opts);
 
 /*
@@ -901,6 +993,7 @@ struct maintenance_task {
 
 enum maintenance_task_label {
 	TASK_PREFETCH,
+	TASK_LOOSE_OBJECTS,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -913,6 +1006,10 @@ static struct maintenance_task tasks[] = {
 		"prefetch",
 		maintenance_task_prefetch,
 	},
+	[TASK_LOOSE_OBJECTS] = {
+		"loose-objects",
+		maintenance_task_loose_objects,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 045524e6ad..b3fc7c8670 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -88,4 +88,43 @@ test_expect_success 'prefetch multiple remotes' '
 	test_cmp_rev refs/remotes/remote2/two refs/prefetch/remote2/two
 '
 
+test_expect_success 'loose-objects task' '
+	# Repack everything so we know the state of the object dir
+	git repack -adk &&
+
+	# Hack to stop maintenance from running during "git commit"
+	echo in use >.git/objects/maintenance.lock &&
+
+	# Assuming that "git commit" creates at least one loose object
+	test_commit create-loose-object &&
+	rm .git/objects/maintenance.lock &&
+
+	ls .git/objects >obj-dir-before &&
+	test_file_not_empty obj-dir-before &&
+	ls .git/objects/pack/*.pack >packs-before &&
+	test_line_count = 1 packs-before &&
+
+	# The first run creates a pack-file
+	# but does not delete loose objects.
+	git maintenance run --task=loose-objects &&
+	ls .git/objects >obj-dir-between &&
+	test_cmp obj-dir-before obj-dir-between &&
+	ls .git/objects/pack/*.pack >packs-between &&
+	test_line_count = 2 packs-between &&
+	ls .git/objects/pack/loose-*.pack >loose-packs &&
+	test_line_count = 1 loose-packs &&
+
+	# The second run deletes loose objects
+	# but does not create a pack-file.
+	git maintenance run --task=loose-objects &&
+	ls .git/objects >obj-dir-after &&
+	cat >expect <<-\EOF &&
+	info
+	pack
+	EOF
+	test_cmp expect obj-dir-after &&
+	ls .git/objects/pack/*.pack >packs-after &&
+	test_cmp packs-between packs-after
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v4 3/8] maintenance: create auto condition for loose-objects
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 2/8] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
@ 2020-09-25 12:33       ` Derrick Stolee via GitGitGadget
  2020-09-25 18:00         ` Junio C Hamano
  2020-09-25 12:33       ` [PATCH v4 4/8] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
                         ` (4 subsequent siblings)
  7 siblings, 1 reply; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-09-25 12:33 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Jonathan Tan,
	Derrick Stolee, Derrick Stolee, Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The loose-objects task deletes loose objects that already exist in a
pack-file, then place the remaining loose objects into a new pack-file.
If this step runs all the time, then we risk creating pack-files with
very few objects with every 'git commit' process. To prevent
overwhelming the packs directory with small pack-files, place a minimum
number of objects to justify the task.

The 'maintenance.loose-objects.auto' config option specifies a minimum
number of loose objects to justify the task to run under the '--auto'
option. This defaults to 100 loose objects. Setting the value to zero
will prevent the step from running under '--auto' while a negative value
will force it to run every time.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/maintenance.txt |  9 +++++++++
 builtin/gc.c                         | 30 ++++++++++++++++++++++++++++
 t/t7900-maintenance.sh               | 22 ++++++++++++++++++++
 3 files changed, 61 insertions(+)

diff --git a/Documentation/config/maintenance.txt b/Documentation/config/maintenance.txt
index 7cc6700d57..c31613be62 100644
--- a/Documentation/config/maintenance.txt
+++ b/Documentation/config/maintenance.txt
@@ -14,3 +14,12 @@ maintenance.commit-graph.auto::
 	reachable commits that are not in the commit-graph file is at least
 	the value of `maintenance.commit-graph.auto`. The default value is
 	100.
+
+maintenance.loose-objects.auto::
+	This integer config option controls how often the `loose-objects` task
+	should be run as part of `git maintenance run --auto`. If zero, then
+	the `loose-objects` task will not run with the `--auto` option. A
+	negative value will force the task to run every time. Otherwise, a
+	positive value implies the command should run when the number of
+	loose objects is at least the value of `maintenance.loose-objects.auto`.
+	The default value is 100.
diff --git a/builtin/gc.c b/builtin/gc.c
index c9db8555b9..4403827481 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -899,6 +899,35 @@ struct write_loose_object_data {
 	int batch_size;
 };
 
+static int loose_object_auto_limit = 100;
+
+static int loose_object_count(const struct object_id *oid,
+			       const char *path,
+			       void *data)
+{
+	int *count = (int*)data;
+	if (++(*count) >= loose_object_auto_limit)
+		return 1;
+	return 0;
+}
+
+static int loose_object_auto_condition(void)
+{
+	int count = 0;
+
+	git_config_get_int("maintenance.loose-objects.auto",
+			   &loose_object_auto_limit);
+
+	if (!loose_object_auto_limit)
+		return 0;
+	if (loose_object_auto_limit < 0)
+		return 1;
+
+	return for_each_loose_file_in_objdir(the_repository->objects->odb->path,
+					     loose_object_count,
+					     NULL, NULL, &count);
+}
+
 static int bail_on_loose(const struct object_id *oid,
 			 const char *path,
 			 void *data)
@@ -1009,6 +1038,7 @@ static struct maintenance_task tasks[] = {
 	[TASK_LOOSE_OBJECTS] = {
 		"loose-objects",
 		maintenance_task_loose_objects,
+		loose_object_auto_condition,
 	},
 	[TASK_GC] = {
 		"gc",
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index b3fc7c8670..27565c55a2 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -127,4 +127,26 @@ test_expect_success 'loose-objects task' '
 	test_cmp packs-between packs-after
 '
 
+test_expect_success 'maintenance.loose-objects.auto' '
+	git repack -adk &&
+	GIT_TRACE2_EVENT="$(pwd)/trace-lo1.txt" \
+		git -c maintenance.loose-objects.auto=1 maintenance \
+		run --auto --task=loose-objects 2>/dev/null &&
+	test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
+	printf data-A | git hash-object -t blob --stdin -w &&
+	GIT_TRACE2_EVENT="$(pwd)/trace-loA" \
+		git -c maintenance.loose-objects.auto=2 \
+		maintenance run --auto --task=loose-objects 2>/dev/null &&
+	test_subcommand ! git prune-packed --quiet <trace-loA &&
+	printf data-B | git hash-object -t blob --stdin -w &&
+	GIT_TRACE2_EVENT="$(pwd)/trace-loB" \
+		git -c maintenance.loose-objects.auto=2 \
+		maintenance run --auto --task=loose-objects 2>/dev/null &&
+	test_subcommand git prune-packed --quiet <trace-loB &&
+	GIT_TRACE2_EVENT="$(pwd)/trace-loC" \
+		git -c maintenance.loose-objects.auto=2 \
+		maintenance run --auto --task=loose-objects 2>/dev/null &&
+	test_subcommand git prune-packed --quiet <trace-loC
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v4 4/8] midx: enable core.multiPackIndex by default
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
                         ` (2 preceding siblings ...)
  2020-09-25 12:33       ` [PATCH v4 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
@ 2020-09-25 12:33       ` Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 5/8] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
                         ` (3 subsequent siblings)
  7 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-09-25 12:33 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Jonathan Tan,
	Derrick Stolee, Derrick Stolee, Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The core.multiPackIndex setting has been around since c4d25228ebb
(config: create core.multiPackIndex setting, 2018-07-12), but has been
disabled by default. If a user wishes to use the multi-pack-index
feature, then they must enable this config and run 'git multi-pack-index
write'.

The multi-pack-index feature is relatively stable now, so make the
config option true by default. For users that do not use a
multi-pack-index, the only extra cost will be a file lookup to see if a
multi-pack-index file exists (once per process, per object directory).

Also, this config option will be referenced by an upcoming
"incremental-repack" task in the maintenance builtin, so move the config
option into the repository settings struct. Note that if
GIT_TEST_MULTI_PACK_INDEX=1, then we want to ignore the config option
and treat core.multiPackIndex as enabled.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/core.txt |  4 ++--
 midx.c                        | 11 +++--------
 repo-settings.c               |  6 ++++++
 repository.h                  |  2 ++
 4 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/Documentation/config/core.txt b/Documentation/config/core.txt
index 74619a9c03..86c91d5381 100644
--- a/Documentation/config/core.txt
+++ b/Documentation/config/core.txt
@@ -606,8 +606,8 @@ core.useReplaceRefs::
 
 core.multiPackIndex::
 	Use the multi-pack-index file to track multiple packfiles using a
-	single index. See link:technical/multi-pack-index.html[the
-	multi-pack-index design document].
+	single index. See linkgit:git-multi-pack-index[1] for more
+	information. Defaults to true.
 
 core.sparseCheckout::
 	Enable "sparse checkout" feature. See linkgit:git-sparse-checkout[1]
diff --git a/midx.c b/midx.c
index a5fb797ede..ef499cf504 100644
--- a/midx.c
+++ b/midx.c
@@ -10,6 +10,7 @@
 #include "progress.h"
 #include "trace2.h"
 #include "run-command.h"
+#include "repository.h"
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
@@ -384,15 +385,9 @@ int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, i
 {
 	struct multi_pack_index *m;
 	struct multi_pack_index *m_search;
-	int config_value;
-	static int env_value = -1;
 
-	if (env_value < 0)
-		env_value = git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0);
-
-	if (!env_value &&
-	    (repo_config_get_bool(r, "core.multipackindex", &config_value) ||
-	    !config_value))
+	prepare_repo_settings(r);
+	if (!r->settings.core_multi_pack_index)
 		return 0;
 
 	for (m_search = r->objects->multi_pack_index; m_search; m_search = m_search->next)
diff --git a/repo-settings.c b/repo-settings.c
index 0918408b34..5bd2c22726 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -1,6 +1,7 @@
 #include "cache.h"
 #include "config.h"
 #include "repository.h"
+#include "midx.h"
 
 #define UPDATE_DEFAULT_BOOL(s,v) do { if (s == -1) { s = v; } } while(0)
 
@@ -47,6 +48,11 @@ void prepare_repo_settings(struct repository *r)
 		r->settings.pack_use_sparse = value;
 	UPDATE_DEFAULT_BOOL(r->settings.pack_use_sparse, 1);
 
+	value = git_env_bool(GIT_TEST_MULTI_PACK_INDEX, 0);
+	if (value || !repo_config_get_bool(r, "core.multipackindex", &value))
+		r->settings.core_multi_pack_index = value;
+	UPDATE_DEFAULT_BOOL(r->settings.core_multi_pack_index, 1);
+
 	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
 		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
diff --git a/repository.h b/repository.h
index 3c1f7d54bd..3901ce0b65 100644
--- a/repository.h
+++ b/repository.h
@@ -37,6 +37,8 @@ struct repo_settings {
 
 	int pack_use_sparse;
 	enum fetch_negotiation_setting fetch_negotiation_algorithm;
+
+	int core_multi_pack_index;
 };
 
 struct repository {
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v4 5/8] midx: use start_delayed_progress()
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
                         ` (3 preceding siblings ...)
  2020-09-25 12:33       ` [PATCH v4 4/8] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
@ 2020-09-25 12:33       ` Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 6/8] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
                         ` (2 subsequent siblings)
  7 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-09-25 12:33 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Jonathan Tan,
	Derrick Stolee, Derrick Stolee, Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

Now that the multi-pack-index may be written as part of auto maintenance
at the end of a command, reduce the progress output when the operations
are quick. Use start_delayed_progress() instead of start_progress().

Update t5319-multi-pack-index.sh to use GIT_PROGRESS_DELAY=0 now that
the progress indicators are conditional.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 midx.c                      | 10 +++++-----
 t/t5319-multi-pack-index.sh | 14 +++++++-------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/midx.c b/midx.c
index ef499cf504..aa37d5da86 100644
--- a/midx.c
+++ b/midx.c
@@ -832,7 +832,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 
 	packs.pack_paths_checked = 0;
 	if (flags & MIDX_PROGRESS)
-		packs.progress = start_progress(_("Adding packfiles to multi-pack-index"), 0);
+		packs.progress = start_delayed_progress(_("Adding packfiles to multi-pack-index"), 0);
 	else
 		packs.progress = NULL;
 
@@ -969,7 +969,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 	}
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Writing chunks to multi-pack-index"),
+		progress = start_delayed_progress(_("Writing chunks to multi-pack-index"),
 					  num_chunks);
 	for (i = 0; i < num_chunks; i++) {
 		if (written != chunk_offsets[i])
@@ -1104,7 +1104,7 @@ int verify_midx_file(struct repository *r, const char *object_dir, unsigned flag
 		return 0;
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Looking for referenced packfiles"),
+		progress = start_delayed_progress(_("Looking for referenced packfiles"),
 					  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
 		if (prepare_midx_pack(r, m, i))
@@ -1225,7 +1225,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 	count = xcalloc(m->num_packs, sizeof(uint32_t));
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Counting referenced objects"),
+		progress = start_delayed_progress(_("Counting referenced objects"),
 					  m->num_objects);
 	for (i = 0; i < m->num_objects; i++) {
 		int pack_int_id = nth_midxed_pack_int_id(m, i);
@@ -1235,7 +1235,7 @@ int expire_midx_packs(struct repository *r, const char *object_dir, unsigned fla
 	stop_progress(&progress);
 
 	if (flags & MIDX_PROGRESS)
-		progress = start_progress(_("Finding and deleting unreferenced packfiles"),
+		progress = start_delayed_progress(_("Finding and deleting unreferenced packfiles"),
 					  m->num_packs);
 	for (i = 0; i < m->num_packs; i++) {
 		char *pack_name;
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 7dfff0f8f4..ec87f616c6 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -171,12 +171,12 @@ test_expect_success 'write progress off for redirected stderr' '
 '
 
 test_expect_success 'write force progress on for stderr' '
-	git multi-pack-index --object-dir=$objdir --progress write 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --progress write 2>err &&
 	test_file_not_empty err
 '
 
 test_expect_success 'write with the --no-progress option' '
-	git multi-pack-index --object-dir=$objdir --no-progress write 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --no-progress write 2>err &&
 	test_line_count = 0 err
 '
 
@@ -333,17 +333,17 @@ test_expect_success 'git-fsck incorrect offset' '
 '
 
 test_expect_success 'repack progress off for redirected stderr' '
-	git multi-pack-index --object-dir=$objdir repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir repack 2>err &&
 	test_line_count = 0 err
 '
 
 test_expect_success 'repack force progress on for stderr' '
-	git multi-pack-index --object-dir=$objdir --progress repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --progress repack 2>err &&
 	test_file_not_empty err
 '
 
 test_expect_success 'repack with the --no-progress option' '
-	git multi-pack-index --object-dir=$objdir --no-progress repack 2>err &&
+	GIT_PROGRESS_DELAY=0 git multi-pack-index --object-dir=$objdir --no-progress repack 2>err &&
 	test_line_count = 0 err
 '
 
@@ -487,7 +487,7 @@ test_expect_success 'expire progress off for redirected stderr' '
 test_expect_success 'expire force progress on for stderr' '
 	(
 		cd dup &&
-		git multi-pack-index --progress expire 2>err &&
+		GIT_PROGRESS_DELAY=0 git multi-pack-index --progress expire 2>err &&
 		test_file_not_empty err
 	)
 '
@@ -495,7 +495,7 @@ test_expect_success 'expire force progress on for stderr' '
 test_expect_success 'expire with the --no-progress option' '
 	(
 		cd dup &&
-		git multi-pack-index --no-progress expire 2>err &&
+		GIT_PROGRESS_DELAY=0 git multi-pack-index --no-progress expire 2>err &&
 		test_line_count = 0 err
 	)
 '
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v4 6/8] maintenance: add incremental-repack task
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
                         ` (4 preceding siblings ...)
  2020-09-25 12:33       ` [PATCH v4 5/8] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
@ 2020-09-25 12:33       ` Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 7/8] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 8/8] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
  7 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-09-25 12:33 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Jonathan Tan,
	Derrick Stolee, Derrick Stolee, Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The previous change cleaned up loose objects using the
'loose-objects' that can be run safely in the background. Add a
similar job that performs similar cleanups for pack-files.

One issue with running 'git repack' is that it is designed to
repack all pack-files into a single pack-file. While this is the
most space-efficient way to store object data, it is not time or
memory efficient. This becomes extremely important if the repo is
so large that a user struggles to store two copies of the pack on
their disk.

Instead, perform an "incremental" repack by collecting a few small
pack-files into a new pack-file. The multi-pack-index facilitates
this process ever since 'git multi-pack-index expire' was added in
19575c7 (multi-pack-index: implement 'expire' subcommand,
2019-06-10) and 'git multi-pack-index repack' was added in ce1e4a1
(midx: implement midx_repack(), 2019-06-10).

The 'incremental-repack' task runs the following steps:

1. 'git multi-pack-index write' creates a multi-pack-index file if
   one did not exist, and otherwise will update the multi-pack-index
   with any new pack-files that appeared since the last write. This
   is particularly relevant with the background fetch job.

   When the multi-pack-index sees two copies of the same object, it
   stores the offset data into the newer pack-file. This means that
   some old pack-files could become "unreferenced" which I will use
   to mean "a pack-file that is in the pack-file list of the
   multi-pack-index but none of the objects in the multi-pack-index
   reference a location inside that pack-file."

2. 'git multi-pack-index expire' deletes any unreferenced pack-files
   and updaes the multi-pack-index to drop those pack-files from the
   list. This is safe to do as concurrent Git processes will see the
   multi-pack-index and not open those packs when looking for object
   contents. (Similar to the 'loose-objects' job, there are some Git
   commands that open pack-files regardless of the multi-pack-index,
   but they are rarely used. Further, a user that self-selects to
   use background operations would likely refrain from using those
   commands.)

3. 'git multi-pack-index repack --bacth-size=<size>' collects a set
   of pack-files that are listed in the multi-pack-index and creates
   a new pack-file containing the objects whose offsets are listed
   by the multi-pack-index to be in those objects. The set of pack-
   files is selected greedily by sorting the pack-files by modified
   time and adding a pack-file to the set if its "expected size" is
   smaller than the batch size until the total expected size of the
   selected pack-files is at least the batch size. The "expected
   size" is calculated by taking the size of the pack-file divided
   by the number of objects in the pack-file and multiplied by the
   number of objects from the multi-pack-index with offset in that
   pack-file. The expected size approximates how much data from that
   pack-file will contribute to the resulting pack-file size. The
   intention is that the resulting pack-file will be close in size
   to the provided batch size.

   The next run of the incremental-repack task will delete these
   repacked pack-files during the 'expire' step.

   In this version, the batch size is set to "0" which ignores the
   size restrictions when selecting the pack-files. It instead
   selects all pack-files and repacks all packed objects into a
   single pack-file. This will be updated in the next change, but
   it requires doing some calculations that are better isolated to
   a separate change.

These steps are based on a similar background maintenance step in
Scalar (and VFS for Git) [1]. This was incredibly effective for
users of the Windows OS repository. After using the same VFS for Git
repository for over a year, some users had _thousands_ of pack-files
that combined to up to 250 GB of data. We noticed a few users were
running into the open file descriptor limits (due in part to a bug
in the multi-pack-index fixed by af96fe3 (midx: add packs to
packed_git linked list, 2019-04-29).

These pack-files were mostly small since they contained the commits
and trees that were pushed to the origin in a given hour. The GVFS
protocol includes a "prefetch" step that asks for pre-computed pack-
files containing commits and trees by timestamp. These pack-files
were grouped into "daily" pack-files once a day for up to 30 days.
If a user did not request prefetch packs for over 30 days, then they
would get the entire history of commits and trees in a new, large
pack-file. This led to a large number of pack-files that had poor
delta compression.

By running this pack-file maintenance step once per day, these repos
with thousands of packs spanning 200+ GB dropped to dozens of pack-
files spanning 30-50 GB. This was done all without removing objects
from the system and using a constant batch size of two gigabytes.
Once the work was done to reduce the pack-files to small sizes, the
batch size of two gigabytes means that not every run triggers a
repack operation, so the following run will not expire a pack-file.
This has kept these repos in a "clean" state.

[1] https://github.com/microsoft/scalar/blob/master/Scalar.Common/Maintenance/PackfileMaintenanceStep.cs

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-maintenance.txt | 18 ++++++++
 builtin/gc.c                      | 76 +++++++++++++++++++++++++++++++
 t/t5319-multi-pack-index.sh       |  1 +
 t/t7900-maintenance.sh            | 38 ++++++++++++++++
 4 files changed, 133 insertions(+)

diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt
index fc95eb594f..3f5d8946b4 100644
--- a/Documentation/git-maintenance.txt
+++ b/Documentation/git-maintenance.txt
@@ -85,6 +85,24 @@ loose-objects::
 	advisable to enable both the `loose-objects` and `gc` tasks at the
 	same time.
 
+incremental-repack::
+	The `incremental-repack` job repacks the object directory
+	using the `multi-pack-index` feature. In order to prevent race
+	conditions with concurrent Git commands, it follows a two-step
+	process. First, it calls `git multi-pack-index expire` to delete
+	pack-files unreferenced by the `multi-pack-index` file. Second, it
+	calls `git multi-pack-index repack` to select several small
+	pack-files and repack them into a bigger one, and then update the
+	`multi-pack-index` entries that refer to the small pack-files to
+	refer to the new pack-file. This prepares those small pack-files
+	for deletion upon the next run of `git multi-pack-index expire`.
+	The selection of the small pack-files is such that the expected
+	size of the big pack-file is at least the batch size; see the
+	`--batch-size` option for the `repack` subcommand in
+	linkgit:git-multi-pack-index[1]. The default batch-size is zero,
+	which is a special case that attempts to repack all pack-files
+	into a single pack-file.
+
 OPTIONS
 -------
 --auto::
diff --git a/builtin/gc.c b/builtin/gc.c
index 4403827481..5f877b097a 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1001,6 +1001,77 @@ static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
 	return prune_packed(opts) || pack_loose(opts);
 }
 
+static int multi_pack_index_write(struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "write", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	if (run_command(&child))
+		return error(_("failed to write multi-pack-index"));
+
+	return 0;
+}
+
+static int multi_pack_index_expire(struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "expire", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	close_object_store(the_repository->objects);
+
+	if (run_command(&child))
+		return error(_("'git multi-pack-index expire' failed"));
+
+	return 0;
+}
+
+static int multi_pack_index_repack(struct maintenance_run_opts *opts)
+{
+	struct child_process child = CHILD_PROCESS_INIT;
+
+	child.git_cmd = 1;
+	strvec_pushl(&child.args, "multi-pack-index", "repack", NULL);
+
+	if (opts->quiet)
+		strvec_push(&child.args, "--no-progress");
+
+	strvec_push(&child.args, "--batch-size=0");
+
+	close_object_store(the_repository->objects);
+
+	if (run_command(&child))
+		return error(_("'git multi-pack-index repack' failed"));
+
+	return 0;
+}
+
+static int maintenance_task_incremental_repack(struct maintenance_run_opts *opts)
+{
+	prepare_repo_settings(the_repository);
+	if (!the_repository->settings.core_multi_pack_index) {
+		warning(_("skipping incremental-repack task because core.multiPackIndex is disabled"));
+		return 0;
+	}
+
+	if (multi_pack_index_write(opts))
+		return 1;
+	if (multi_pack_index_expire(opts))
+		return 1;
+	if (multi_pack_index_repack(opts))
+		return 1;
+	return 0;
+}
+
 typedef int maintenance_task_fn(struct maintenance_run_opts *opts);
 
 /*
@@ -1023,6 +1094,7 @@ struct maintenance_task {
 enum maintenance_task_label {
 	TASK_PREFETCH,
 	TASK_LOOSE_OBJECTS,
+	TASK_INCREMENTAL_REPACK,
 	TASK_GC,
 	TASK_COMMIT_GRAPH,
 
@@ -1040,6 +1112,10 @@ static struct maintenance_task tasks[] = {
 		maintenance_task_loose_objects,
 		loose_object_auto_condition,
 	},
+	[TASK_INCREMENTAL_REPACK] = {
+		"incremental-repack",
+		maintenance_task_incremental_repack,
+	},
 	[TASK_GC] = {
 		"gc",
 		maintenance_task_gc,
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index ec87f616c6..2f942ee1fa 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -3,6 +3,7 @@
 test_description='multi-pack-indexes'
 . ./test-lib.sh
 
+GIT_TEST_MULTI_PACK_INDEX=0
 objdir=.git/objects
 
 midx_read_expect () {
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 27565c55a2..a2db2291b0 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -5,6 +5,7 @@ test_description='git maintenance builtin'
 . ./test-lib.sh
 
 GIT_TEST_COMMIT_GRAPH=0
+GIT_TEST_MULTI_PACK_INDEX=0
 
 test_expect_success 'help text' '
 	test_expect_code 129 git maintenance -h 2>err &&
@@ -149,4 +150,41 @@ test_expect_success 'maintenance.loose-objects.auto' '
 	test_subcommand git prune-packed --quiet <trace-loC
 '
 
+test_expect_success 'incremental-repack task' '
+	packDir=.git/objects/pack &&
+	for i in $(test_seq 1 5)
+	do
+		test_commit $i || return 1
+	done &&
+
+	# Create three disjoint pack-files with size BIG, small, small.
+	echo HEAD~2 | git pack-objects --revs $packDir/test-1 &&
+	test_tick &&
+	git pack-objects --revs $packDir/test-2 <<-\EOF &&
+	HEAD~1
+	^HEAD~2
+	EOF
+	test_tick &&
+	git pack-objects --revs $packDir/test-3 <<-\EOF &&
+	HEAD
+	^HEAD~1
+	EOF
+	rm -f $packDir/pack-* &&
+	rm -f $packDir/loose-* &&
+	ls $packDir/*.pack >packs-before &&
+	test_line_count = 3 packs-before &&
+
+	# the job repacks the two into a new pack, but does not
+	# delete the old ones.
+	git maintenance run --task=incremental-repack &&
+	ls $packDir/*.pack >packs-between &&
+	test_line_count = 4 packs-between &&
+
+	# the job deletes the two old packs, and does not write
+	# a new one because only one pack remains.
+	git maintenance run --task=incremental-repack &&
+	ls .git/objects/pack/*.pack >packs-after &&
+	test_line_count = 1 packs-after
+'
+
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v4 7/8] maintenance: auto-size incremental-repack batch
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
                         ` (5 preceding siblings ...)
  2020-09-25 12:33       ` [PATCH v4 6/8] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
@ 2020-09-25 12:33       ` Derrick Stolee via GitGitGadget
  2020-09-25 12:33       ` [PATCH v4 8/8] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
  7 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-09-25 12:33 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Jonathan Tan,
	Derrick Stolee, Derrick Stolee, Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

When repacking during the 'incremental-repack' task, we use the
--batch-size option in 'git multi-pack-index repack'. The initial setting
used --batch-size=0 to repack everything into a single pack-file. This is
not sustainable for a large repository. The amount of work required is
also likely to use too many system resources for a background job.

Update the 'incremental-repack' task by dynamically computing a
--batch-size option based on the current pack-file structure.

The dynamic default size is computed with this idea in mind for a client
repository that was cloned from a very large remote: there is likely one
"big" pack-file that was created at clone time. Thus, do not try
repacking it as it is likely packed efficiently by the server.

Instead, we select the second-largest pack-file, and create a batch size
that is one larger than that pack-file. If there are three or more
pack-files, then this guarantees that at least two will be combined into
a new pack-file.

Of course, this means that the second-largest pack-file size is likely
to grow over time and may eventually surpass the initially-cloned
pack-file. Recall that the pack-file batch is selected in a greedy
manner: the packs are considered from oldest to newest and are selected
if they have size smaller than the batch size until the total selected
size is larger than the batch size. Thus, that oldest "clone" pack will
be first to repack after the new data creates a pack larger than that.

We also want to place some limits on how large these pack-files become,
in order to bound the amount of time spent repacking. A maximum
batch-size of two gigabytes means that large repositories will never be
packed into a single pack-file using this job, but also that repack is
rather expensive. This is a trade-off that is valuable to have if the
maintenance is being run automatically or in the background. Users who
truly want to optimize for space and performance (and are willing to pay
the upfront cost of a full repack) can use the 'gc' task to do so.

Create a test for this two gigabyte limit by creating an EXPENSIVE test
that generates two pack-files of roughly 2.5 gigabytes in size, then
performs an incremental repack. Check that the --batch-size argument in
the subcommand uses the hard-coded maximum.

Helped-by: Chris Torek <chris.torek@gmail.com>
Reported-by: Son Luong Ngoc <sluongng@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 builtin/gc.c           | 43 +++++++++++++++++++++++++++++++++++++++++-
 t/t7900-maintenance.sh | 36 +++++++++++++++++++++++++++++++++--
 2 files changed, 76 insertions(+), 3 deletions(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 5f877b097a..8d22361fa9 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1035,6 +1035,46 @@ static int multi_pack_index_expire(struct maintenance_run_opts *opts)
 	return 0;
 }
 
+#define TWO_GIGABYTES (INT32_MAX)
+
+static off_t get_auto_pack_size(void)
+{
+	/*
+	 * The "auto" value is special: we optimize for
+	 * one large pack-file (i.e. from a clone) and
+	 * expect the rest to be small and they can be
+	 * repacked quickly.
+	 *
+	 * The strategy we select here is to select a
+	 * size that is one more than the second largest
+	 * pack-file. This ensures that we will repack
+	 * at least two packs if there are three or more
+	 * packs.
+	 */
+	off_t max_size = 0;
+	off_t second_largest_size = 0;
+	off_t result_size;
+	struct packed_git *p;
+	struct repository *r = the_repository;
+
+	reprepare_packed_git(r);
+	for (p = get_all_packs(r); p; p = p->next) {
+		if (p->pack_size > max_size) {
+			second_largest_size = max_size;
+			max_size = p->pack_size;
+		} else if (p->pack_size > second_largest_size)
+			second_largest_size = p->pack_size;
+	}
+
+	result_size = second_largest_size + 1;
+
+	/* But limit ourselves to a batch size of 2g */
+	if (result_size > TWO_GIGABYTES)
+		result_size = TWO_GIGABYTES;
+
+	return result_size;
+}
+
 static int multi_pack_index_repack(struct maintenance_run_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -1045,7 +1085,8 @@ static int multi_pack_index_repack(struct maintenance_run_opts *opts)
 	if (opts->quiet)
 		strvec_push(&child.args, "--no-progress");
 
-	strvec_push(&child.args, "--batch-size=0");
+	strvec_pushf(&child.args, "--batch-size=%"PRIuMAX,
+				  (uintmax_t)get_auto_pack_size());
 
 	close_object_store(the_repository->objects);
 
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index a2db2291b0..9e6ea23f35 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -181,10 +181,42 @@ test_expect_success 'incremental-repack task' '
 	test_line_count = 4 packs-between &&
 
 	# the job deletes the two old packs, and does not write
-	# a new one because only one pack remains.
+	# a new one because the batch size is not high enough to
+	# pack the largest pack-file.
 	git maintenance run --task=incremental-repack &&
 	ls .git/objects/pack/*.pack >packs-after &&
-	test_line_count = 1 packs-after
+	test_line_count = 2 packs-after
+'
+
+test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
+	for i in $(test_seq 1 5)
+	do
+		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
+		return 1
+	done &&
+	git add big &&
+	git commit -m "Add big file (1)" &&
+
+	# ensure any possible loose objects are in a pack-file
+	git maintenance run --task=loose-objects &&
+
+	rm big &&
+	for i in $(test_seq 6 10)
+	do
+		test-tool genrandom foo$i $((512 * 1024 * 1024 + 1)) >>big ||
+		return 1
+	done &&
+	git add big &&
+	git commit -m "Add big file (2)" &&
+
+	# ensure any possible loose objects are in a pack-file
+	git maintenance run --task=loose-objects &&
+
+	# Now run the incremental-repack task and check the batch-size
+	GIT_TRACE2_EVENT="$(pwd)/run-2g.txt" git maintenance run \
+		--task=incremental-repack 2>/dev/null &&
+	test_subcommand git multi-pack-index repack \
+		 --no-progress --batch-size=2147483647 <run-2g.txt
 '
 
 test_done
-- 
gitgitgadget


^ permalink raw reply	[flat|nested] 66+ messages in thread

* [PATCH v4 8/8] maintenance: add incremental-repack auto condition
  2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
                         ` (6 preceding siblings ...)
  2020-09-25 12:33       ` [PATCH v4 7/8] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
@ 2020-09-25 12:33       ` Derrick Stolee via GitGitGadget
  7 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee via GitGitGadget @ 2020-09-25 12:33 UTC (permalink / raw)
  To: git
  Cc: sandals, steadmon, jrnieder, peff, congdanhqx, phillip.wood123,
	emilyshaffer, sluongng, jonathantanmy, Jonathan Tan,
	Derrick Stolee, Derrick Stolee, Derrick Stolee

From: Derrick Stolee <dstolee@microsoft.com>

The incremental-repack task updates the multi-pack-index by deleting pack-
files that have been replaced with new packs, then repacking a batch of
small pack-files into a larger pack-file. This incremental repack is faster
than rewriting all object data, but is slower than some other
maintenance activities.

The 'maintenance.incremental-repack.auto' config option specifies how many
pack-files should exist outside of the multi-pack-index before running
the step. These pack-files could be created by 'git fetch' commands or
by the loose-objects task. The default value is 10.

Setting the option to zero disables the task with the '--auto' option,
and a negative value makes the task run every time.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/config/maintenance.txt |  9 ++++++++
 builtin/gc.c                         | 31 ++++++++++++++++++++++++++++
 t/t7900-maintenance.sh               | 28 +++++++++++++++++++++++++
 3 files changed, 68 insertions(+)

diff --git a/Documentation/config/maintenance.txt b/Documentation/config/maintenance.txt
index c31613be62..a0706d8f09 100644
--- a/Documentation/config/maintenance.txt
+++ b/Documentation/config/maintenance.txt
@@ -23,3 +23,12 @@ maintenance.loose-objects.auto::
 	positive value implies the command should run when the number of
 	loose objects is at least the value of `maintenance.loose-objects.auto`.
 	The default value is 100.
+
+maintenance.incremental-repack.auto::
+	This integer config option controls how often the `incremental-repack`
+	task should be run as part of `git maintenance run --auto`. If zero,
+	then the `incremental-repack` task will not run with the `--auto`
+	option. A negative value will force the task to run every time.
+	Otherwise, a positive value implies the command should run when the
+	number of pack-files not in the multi-pack-index is at least the value
+	of `maintenance.incremental-repack.auto`. The default value is 10.
diff --git a/builtin/gc.c b/builtin/gc.c
index 8d22361fa9..2b99596ec8 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -30,6 +30,7 @@
 #include "promisor-remote.h"
 #include "refs.h"
 #include "remote.h"
+#include "object-store.h"
 
 #define FAILED_RUN "failed to run %s"
 
@@ -1001,6 +1002,35 @@ static int maintenance_task_loose_objects(struct maintenance_run_opts *opts)
 	return prune_packed(opts) || pack_loose(opts);
 }
 
+static int incremental_repack_auto_condition(void)
+{
+	struct packed_git *p;
+	int enabled;
+	int incremental_repack_auto_limit = 10;
+	int count = 0;
+
+	if (git_config_get_bool("core.multiPackIndex", &enabled) ||
+	    !enabled)
+		return 0;
+
+	git_config_get_int("maintenance.incremental-repack.auto",
+			   &incremental_repack_auto_limit);
+
+	if (!incremental_repack_auto_limit)
+		return 0;
+	if (incremental_repack_auto_limit < 0)
+		return 1;
+
+	for (p = get_packed_git(the_repository);
+	     count < incremental_repack_auto_limit && p;
+	     p = p->next) {
+		if (!p->multi_pack_index)
+			count++;
+	}
+
+	return count >= incremental_repack_auto_limit;
+}
+
 static int multi_pack_index_write(struct maintenance_run_opts *opts)
 {
 	struct child_process child = CHILD_PROCESS_INIT;
@@ -1156,6 +1186,7 @@ static struct maintenance_task tasks[] = {
 	[TASK_INCREMENTAL_REPACK] = {
 		"incremental-repack",
 		maintenance_task_incremental_repack,
+		incremental_repack_auto_condition,
 	},
 	[TASK_GC] = {
 		"gc",
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index 9e6ea23f35..55116c2f04 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -219,4 +219,32 @@ test_expect_success EXPENSIVE 'incremental-repack 2g limit' '
 		 --no-progress --batch-size=2147483647 <run-2g.txt
 '
 
+test_expect_success 'maintenance.incremental-repack.auto' '
+	git repack -adk &&
+	git config core.multiPackIndex true &&
+	git multi-pack-index write &&
+	GIT_TRACE2_EVENT="$(pwd)/midx-init.txt" git \
+		-c maintenance.incremental-repack.auto=1 \
+		maintenance run --auto --task=incremental-repack 2>/dev/null &&
+	test_subcommand ! git multi-pack-index write --no-progress <midx-init.txt &&
+	test_commit A &&
+	git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
+	HEAD
+	^HEAD~1
+	EOF
+	GIT_TRACE2_EVENT=$(pwd)/trace-A git \
+		-c maintenance.incremental-repack.auto=2 \
+		maintenance run --auto --task=incremental-repack 2>/dev/null &&
+	test_subcommand ! git multi-pack-index write --no-progress <trace-A &&
+	test_commit B &&
+	git pack-objects --revs .git/objects/pack/pack <<-\EOF &&
+	HEAD
+	^HEAD~1
+	EOF
+	GIT_TRACE2_EVENT=$(pwd)/trace-B git \
+		-c maintenance.incremental-repack.auto=2 \
+		maintenance run --auto --task=incremental-repack 2>/dev/null &&
+	test_subcommand git multi-pack-index write --no-progress <trace-B
+'
+
 test_done
-- 
gitgitgadget

^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v4 3/8] maintenance: create auto condition for loose-objects
  2020-09-25 12:33       ` [PATCH v4 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
@ 2020-09-25 18:00         ` Junio C Hamano
  2020-09-25 18:43           ` Derrick Stolee
  0 siblings, 1 reply; 66+ messages in thread
From: Junio C Hamano @ 2020-09-25 18:00 UTC (permalink / raw)
  To: Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, jonathantanmy,
	Derrick Stolee, Derrick Stolee, Derrick Stolee

"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
> index b3fc7c8670..27565c55a2 100755
> --- a/t/t7900-maintenance.sh
> +++ b/t/t7900-maintenance.sh
> @@ -127,4 +127,26 @@ test_expect_success 'loose-objects task' '
>  	test_cmp packs-between packs-after
>  '
>  
> +test_expect_success 'maintenance.loose-objects.auto' '
> +	git repack -adk &&
> +	GIT_TRACE2_EVENT="$(pwd)/trace-lo1.txt" \
> +		git -c maintenance.loose-objects.auto=1 maintenance \
> +		run --auto --task=loose-objects 2>/dev/null &&
> +	test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
> +	printf data-A | git hash-object -t blob --stdin -w &&
> +	GIT_TRACE2_EVENT="$(pwd)/trace-loA" \
> +		git -c maintenance.loose-objects.auto=2 \
> +		maintenance run --auto --task=loose-objects 2>/dev/null &&
> +	test_subcommand ! git prune-packed --quiet <trace-loA &&
> +	printf data-B | git hash-object -t blob --stdin -w &&

Is it essential for the purpose of the test somehow that the data
used for the test are all incomplete files that lack the end-of-line
at the end of the file?  Use of 'printf' sends such a signal to
confuse readers.

Use of test_write_lines to write a single line may feel overkill,
but it may be less cryptic, as newer parts of testsuite are
encouraged to use it over 'echo' and raw 'printf'.

> +	GIT_TRACE2_EVENT="$(pwd)/trace-loB" \
> +		git -c maintenance.loose-objects.auto=2 \
> +		maintenance run --auto --task=loose-objects 2>/dev/null &&
> +	test_subcommand git prune-packed --quiet <trace-loB &&
> +	GIT_TRACE2_EVENT="$(pwd)/trace-loC" \
> +		git -c maintenance.loose-objects.auto=2 \
> +		maintenance run --auto --task=loose-objects 2>/dev/null &&
> +	test_subcommand git prune-packed --quiet <trace-loC
> +'


^ permalink raw reply	[flat|nested] 66+ messages in thread

* Re: [PATCH v4 3/8] maintenance: create auto condition for loose-objects
  2020-09-25 18:00         ` Junio C Hamano
@ 2020-09-25 18:43           ` Derrick Stolee
  0 siblings, 0 replies; 66+ messages in thread
From: Derrick Stolee @ 2020-09-25 18:43 UTC (permalink / raw)
  To: Junio C Hamano, Derrick Stolee via GitGitGadget
  Cc: git, sandals, steadmon, jrnieder, peff, congdanhqx,
	phillip.wood123, emilyshaffer, sluongng, jonathantanmy,
	Derrick Stolee, Derrick Stolee

On 9/25/2020 2:00 PM, Junio C Hamano wrote:
> "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:
>> +	printf data-B | git hash-object -t blob --stdin -w &&
> 
> Is it essential for the purpose of the test somehow that the data
> used for the test are all incomplete files that lack the end-of-line
> at the end of the file?  Use of 'printf' sends such a signal to
> confuse readers.
> 
> Use of test_write_lines to write a single line may feel overkill,
> but it may be less cryptic, as newer parts of testsuite are
> encouraged to use it over 'echo' and raw 'printf'.

I suppose it could be more standard. It's not particularly
important what the data is here, so lacking a newline seems
innocuous enough to me. I'm happy to agree with standards
elsewhere to avoid being a bad example.

A simple s/printf/test_write_lines/ appears to do the trick:

diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index f259485990..a1bd0029c6 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -147,12 +147,12 @@ test_expect_success 'maintenance.loose-objects.auto' '
                git -c maintenance.loose-objects.auto=1 maintenance \
                run --auto --task=loose-objects 2>/dev/null &&
        test_subcommand ! git prune-packed --quiet <trace-lo1.txt &&
-       printf data-A | git hash-object -t blob --stdin -w &&
+       test_write_lines data-A | git hash-object -t blob --stdin -w &&
        GIT_TRACE2_EVENT="$(pwd)/trace-loA" \
                git -c maintenance.loose-objects.auto=2 \
                maintenance run --auto --task=loose-objects 2>/dev/null &&
        test_subcommand ! git prune-packed --quiet <trace-loA &&
-       printf data-B | git hash-object -t blob --stdin -w &&
+       test_write_lines data-B | git hash-object -t blob --stdin -w &&
        GIT_TRACE2_EVENT="$(pwd)/trace-loB" \
                git -c maintenance.loose-objects.auto=2 \
                maintenance run --auto --task=loose-objects 2>/dev/null &&

Thanks,
-Stolee

^ permalink raw reply	[flat|nested] 66+ messages in thread

end of thread, other threads:[~2020-09-25 18:43 UTC | newest]

Thread overview: 66+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-06 16:30 [PATCH 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
2020-08-12 23:10   ` Emily Shaffer
2020-08-13  0:03     ` Junio C Hamano
2020-08-13  1:45       ` Jonathan Nieder
2020-08-13  4:37       ` [PATCH v3] " Junio C Hamano
2020-08-14  1:13         ` Derrick Stolee
2020-08-14  1:32           ` Junio C Hamano
2020-08-06 16:30 ` [PATCH 2/9] maintenance: add prefetch task Derrick Stolee via GitGitGadget
2020-08-12 23:10   ` Emily Shaffer
2020-08-14  1:28     ` Derrick Stolee
2020-08-06 16:30 ` [PATCH 3/9] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
2020-08-12 23:10   ` Emily Shaffer
2020-08-14  1:46     ` Derrick Stolee
2020-08-06 16:30 ` [PATCH 4/9] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 5/9] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 6/9] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 7/9] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
2020-08-06 16:30 ` [PATCH 8/9] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
2020-08-06 17:02   ` Son Luong Ngoc
2020-08-06 18:13     ` Derrick Stolee
2020-08-06 16:30 ` [PATCH 9/9] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
2020-08-18 14:25 ` [PATCH v2 0/9] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 1/9] fetch: optionally allow disabling FETCH_HEAD update Junio C Hamano via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 2/9] maintenance: add prefetch task Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 3/9] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 4/9] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 5/9] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 6/9] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 7/9] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 8/9] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
2020-08-18 14:25   ` [PATCH v2 9/9] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
2020-08-25 18:36   ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Derrick Stolee via GitGitGadget
2020-08-25 18:36     ` [PATCH v3 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
2020-09-22 23:05       ` Jonathan Tan
2020-08-25 18:36     ` [PATCH v3 2/8] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
2020-09-22 23:09       ` Jonathan Tan
2020-09-24 13:45         ` Derrick Stolee
2020-08-25 18:36     ` [PATCH v3 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
2020-09-22 23:15       ` Jonathan Tan
2020-09-24 13:51         ` Derrick Stolee
2020-08-25 18:36     ` [PATCH v3 4/8] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
2020-09-22 23:16       ` Jonathan Tan
2020-09-24 13:53         ` Derrick Stolee
2020-08-25 18:36     ` [PATCH v3 5/8] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
2020-08-25 18:36     ` [PATCH v3 6/8] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
2020-09-22 23:26       ` Jonathan Tan
2020-09-24 14:05         ` Derrick Stolee
2020-09-24 22:01           ` Jonathan Tan
2020-08-25 18:36     ` [PATCH v3 7/8] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
2020-08-25 18:36     ` [PATCH v3 8/8] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget
2020-09-22 23:52       ` Jonathan Tan
2020-08-25 20:59     ` [PATCH v3 0/8] Maintenance II: prefetch, loose-objects, incremental-repack tasks Junio C Hamano
2020-08-26 15:15     ` Son Luong Ngoc
2020-08-26 16:21       ` Derrick Stolee
2020-09-25 12:33     ` [PATCH v4 " Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 1/8] maintenance: add prefetch task Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 2/8] maintenance: add loose-objects task Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 3/8] maintenance: create auto condition for loose-objects Derrick Stolee via GitGitGadget
2020-09-25 18:00         ` Junio C Hamano
2020-09-25 18:43           ` Derrick Stolee
2020-09-25 12:33       ` [PATCH v4 4/8] midx: enable core.multiPackIndex by default Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 5/8] midx: use start_delayed_progress() Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 6/8] maintenance: add incremental-repack task Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 7/8] maintenance: auto-size incremental-repack batch Derrick Stolee via GitGitGadget
2020-09-25 12:33       ` [PATCH v4 8/8] maintenance: add incremental-repack auto condition Derrick Stolee via GitGitGadget

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