From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by dcvr.yhbt.net (Postfix) with ESMTP id 9FD8B1F5AE for ; Thu, 23 Jul 2020 17:57:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730258AbgGWR46 (ORCPT ); Thu, 23 Jul 2020 13:56:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53302 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730236AbgGWR4x (ORCPT ); Thu, 23 Jul 2020 13:56:53 -0400 Received: from mail-wr1-x441.google.com (mail-wr1-x441.google.com [IPv6:2a00:1450:4864:20::441]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 79477C0619E5 for ; Thu, 23 Jul 2020 10:56:53 -0700 (PDT) Received: by mail-wr1-x441.google.com with SMTP id r4so3048061wrx.9 for ; Thu, 23 Jul 2020 10:56:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=message-id:in-reply-to:references:from:date:subject:fcc :content-transfer-encoding:mime-version:to:cc; bh=4V4l1GzGZeC37+TbBBvEXaX6tBlf7EXxL2Zke8V3noE=; b=ZO6bNkCzkLJL8DPreSk9AMeVZSLMpV+y0nywSAZHFGkDH7VWg+JE6vMq9dffNA0Oke 5e71KOUKEwXkwRo6GCzhGHR6zD56hFQLhp6hFREpGpLVy2pV9lq5Hr+7pK6x9Rir6TVt FQtaWkFVg9UF4T23enPkRhZc3SGmuso2+QQ2pjWosD411h956cvinMBNZgbQlCGkQbzp 0xhXbg2QZ+RMY7oAm7/iYcinkYW83xl+6WnQoRUOfkc6C/9Nt51+oDzsi31FWyR8kM0Z TcuhVjzFj9hJxiSn8rk8LZPAZd+nmeFm0ZqzCB5BNVdB6EL0CwLsPm3vSkSbIvdNOEkC MNXA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:in-reply-to:references:from:date :subject:fcc:content-transfer-encoding:mime-version:to:cc; bh=4V4l1GzGZeC37+TbBBvEXaX6tBlf7EXxL2Zke8V3noE=; b=NAh8s46WfHXm80f4/Ys4msZZVOsofeUIUNDdrd8eRTJKZHOOXvwg/awYNBZXHWSO/9 JP8C+anlrUrpHRood53A7dQMc4yVf3LjzyvtoYQ5Cl/pT1wguqWduR9KGyhUzn/RRVUq 5JnKy9/ONK/ApWi3QuogLUgTcXBSMmlzunPIQ5N7VjV4N38jm6vRXM3AdzfoVmSKTra/ PqZsjtfe3dbPuzGATui+xEvf/GhzsZlqSgEznknyCNFDsfUFcCOMAtuo3iHVl9C0ZD1b oViC3ozLcWl6KKkfFRQkB2JAYuJ8yVcppWTHNQVe8I5xFGRUzYwCvutKznkn08jlVjuQ 8S3w== X-Gm-Message-State: AOAM531zogdeJnKbVzpmQEnOqIRuID60RxvB2gw4ke6lOqgIqihMqG0W 3rFNt72rc4oZl3gZg8e1Vja6O9zJ X-Google-Smtp-Source: ABdhPJzeuJTtXK/wpiWmB43tDHuQHIkJX+YEBO+FuIl8s2acb1wR5BWW0nZA1jdbu1GAM0HHCSztjQ== X-Received: by 2002:adf:8024:: with SMTP id 33mr5472585wrk.117.1595527011708; Thu, 23 Jul 2020 10:56:51 -0700 (PDT) Received: from [127.0.0.1] ([13.74.141.28]) by smtp.gmail.com with ESMTPSA id e5sm5044835wrc.37.2020.07.23.10.56.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jul 2020 10:56:51 -0700 (PDT) Message-Id: In-Reply-To: References: From: "Derrick Stolee via GitGitGadget" Date: Thu, 23 Jul 2020 17:56:32 +0000 Subject: [PATCH v2 10/18] maintenance: add incremental-repack task Fcc: Sent Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit MIME-Version: 1.0 To: git@vger.kernel.org Cc: Johannes.Schindelin@gmx.de, sandals@crustytoothpaste.net, steadmon@google.com, jrnieder@gmail.com, peff@peff.net, congdanhqx@gmail.com, phillip.wood123@gmail.com, emilyshaffer@google.com, sluongng@gmail.com, jonathantanmy@google.com, Derrick Stolee , Derrick Stolee Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org From: Derrick Stolee 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=' 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 approximats 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 --- Documentation/git-maintenance.txt | 15 ++++ builtin/gc.c | 121 +++++++++++++++++++++++++++++- midx.c | 2 +- midx.h | 1 + t/t7900-maintenance.sh | 37 +++++++++ 5 files changed, 174 insertions(+), 2 deletions(-) diff --git a/Documentation/git-maintenance.txt b/Documentation/git-maintenance.txt index 557915a653..bda8df4aaa 100644 --- a/Documentation/git-maintenance.txt +++ b/Documentation/git-maintenance.txt @@ -84,6 +84,21 @@ 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 fa65304580..eb4b01c104 100644 --- a/builtin/gc.c +++ b/builtin/gc.c @@ -29,6 +29,7 @@ #include "tree.h" #include "promisor-remote.h" #include "remote.h" +#include "midx.h" #define FAILED_RUN "failed to run %s" @@ -701,7 +702,7 @@ int cmd_gc(int argc, const char **argv, const char *prefix) return 0; } -#define MAX_NUM_TASKS 4 +#define MAX_NUM_TASKS 5 static const char * const builtin_maintenance_usage[] = { N_("git maintenance run []"), @@ -958,6 +959,120 @@ static int maintenance_task_loose_objects(void) return prune_packed() || pack_loose(); } +static int multi_pack_index_write(void) +{ + int result; + struct argv_array cmd = ARGV_ARRAY_INIT; + argv_array_pushl(&cmd, "multi-pack-index", "write", NULL); + + if (opts.quiet) + argv_array_push(&cmd, "--no-progress"); + + result = run_command_v_opt(cmd.argv, RUN_GIT_CMD); + argv_array_clear(&cmd); + + return result; +} + +static int rewrite_multi_pack_index(void) +{ + struct repository *r = the_repository; + char *midx_name = get_midx_filename(r->objects->odb->path); + + unlink(midx_name); + free(midx_name); + + if (multi_pack_index_write()) { + error(_("failed to rewrite multi-pack-index")); + return 1; + } + + return 0; +} + +static int multi_pack_index_verify(void) +{ + int result; + struct argv_array cmd = ARGV_ARRAY_INIT; + argv_array_pushl(&cmd, "multi-pack-index", "verify", NULL); + + if (opts.quiet) + argv_array_push(&cmd, "--no-progress"); + + result = run_command_v_opt(cmd.argv, RUN_GIT_CMD); + argv_array_clear(&cmd); + + return result; +} + +static int multi_pack_index_expire(void) +{ + int result; + struct argv_array cmd = ARGV_ARRAY_INIT; + argv_array_pushl(&cmd, "multi-pack-index", "expire", NULL); + + if (opts.quiet) + argv_array_push(&cmd, "--no-progress"); + + close_object_store(the_repository->objects); + result = run_command_v_opt(cmd.argv, RUN_GIT_CMD); + argv_array_clear(&cmd); + + return result; +} + +static int multi_pack_index_repack(void) +{ + int result; + struct argv_array cmd = ARGV_ARRAY_INIT; + argv_array_pushl(&cmd, "multi-pack-index", "repack", NULL); + + if (opts.quiet) + argv_array_push(&cmd, "--no-progress"); + + argv_array_push(&cmd, "--batch-size=0"); + + close_object_store(the_repository->objects); + result = run_command_v_opt(cmd.argv, RUN_GIT_CMD); + + if (result && multi_pack_index_verify()) { + warning(_("multi-pack-index verify failed after repack")); + result = rewrite_multi_pack_index(); + } + + return result; +} + +static int maintenance_task_incremental_repack(void) +{ + if (multi_pack_index_write()) { + error(_("failed to write multi-pack-index")); + return 1; + } + + if (multi_pack_index_verify()) { + warning(_("multi-pack-index verify failed after initial write")); + return rewrite_multi_pack_index(); + } + + if (multi_pack_index_expire()) { + error(_("multi-pack-index expire failed")); + return 1; + } + + if (multi_pack_index_verify()) { + warning(_("multi-pack-index verify failed after expire")); + return rewrite_multi_pack_index(); + } + + if (multi_pack_index_repack()) { + error(_("multi-pack-index repack failed")); + return 1; + } + + return 0; +} + typedef int maintenance_task_fn(void); struct maintenance_task { @@ -1037,6 +1152,10 @@ static void initialize_tasks(void) tasks[num_tasks]->fn = maintenance_task_loose_objects; num_tasks++; + tasks[num_tasks]->name = "incremental-repack"; + tasks[num_tasks]->fn = maintenance_task_incremental_repack; + num_tasks++; + tasks[num_tasks]->name = "gc"; tasks[num_tasks]->fn = maintenance_task_gc; tasks[num_tasks]->enabled = 1; diff --git a/midx.c b/midx.c index 6d1584ca51..57a8a00082 100644 --- a/midx.c +++ b/midx.c @@ -36,7 +36,7 @@ #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/t7900-maintenance.sh b/t/t7900-maintenance.sh index 94bb493733..3ec813979a 100755 --- a/t/t7900-maintenance.sh +++ b/t/t7900-maintenance.sh @@ -103,4 +103,41 @@ test_expect_success 'loose-objects task' ' test_cmp packs-between packs-after ' +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