[PATCH 0/7] Maintenance III: Background maintenance

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

This is based on ds/maintenance-part-2 and replaces the RFC from [1].

[1] 
https://lore.kernel.org/git/pull.680.v3.git.1598629517.gitgitgadget@gmail.com/

This series introduces background maintenance to Git, through an integration
with cron and crontab.

Some preliminary work is done to allow a new --schedule option that tells
the command which tasks to run based on a maintenance.<task>.schedule config
option. The timing is not enforced by Git, but instead is expected to be
provided as a hint from a cron schedule. The options are "hourly", "daily",
and "weekly".

A new for-each-repo builtin runs Git commands on every repo in a given list.
Currently, the list is stored as a config setting, allowing a new 
maintenance.repos config list to store the repositories registered for
background maintenance. Others may want to add a --file=<file> option for
their own workflows, but I focused on making this as simple as possible for
now.

The updates to the git maintenance builtin include new register/unregister 
subcommands and start/stop subcommands. The register subcommand initializes
the config while the start subcommand does everything register does plus 
update the cron table. The unregister and stop commands reverse this
process.

A troubleshooting guide is added to Documentation/git-maintenance.txt to
advise expert users who choose to create custom cron schedules.

The very last patch is entirely optional. It sets a recommended schedule
based on my own experience with very large repositories. I'm open to other
suggestions, but these are ones that I think work well and don't cause a
"rewrite the world" scenario like running nightly 'gc' would do.

I've been testing this scenario on my macOS laptop and Linux desktop. I have
modified my cron task to provide logging via trace2 so I can see what's
happening. A future direction here would be to add some maintenance logs to
the repository so we can track what is happening and diagnose whether the
maintenance strategy is working on real repos.

Note: git maintenance (start|stop) only works on machines with cron by
design. The proper thing to do on Windows will come later. Perhaps this
command should be marked as unavailable on Windows somehow, or at least a
better error than "cron may not be available on your system". I did find
that that message is helpful sometimes: macOS worker agents for CI builds
typically do not have cron available.

Derrick Stolee (7):
  maintenance: optionally skip --auto process
  maintenance: add --schedule option and config
  for-each-repo: run subcommands on configured repos
  maintenance: add [un]register subcommands
  maintenance: add start/stop subcommands
  maintenance: recommended schedule in register/start
  maintenance: add troubleshooting guide to docs

 .gitignore                           |   1 +
 Documentation/config/maintenance.txt |  10 +
 Documentation/git-for-each-repo.txt  |  59 ++++++
 Documentation/git-maintenance.txt    |  88 +++++++-
 Makefile                             |   2 +
 builtin.h                            |   1 +
 builtin/for-each-repo.c              |  58 ++++++
 builtin/gc.c                         | 292 ++++++++++++++++++++++++++-
 command-list.txt                     |   1 +
 git.c                                |   1 +
 run-command.c                        |   6 +
 t/helper/test-crontab.c              |  35 ++++
 t/helper/test-tool.c                 |   1 +
 t/helper/test-tool.h                 |   1 +
 t/t0068-for-each-repo.sh             |  30 +++
 t/t7900-maintenance.sh               | 114 ++++++++++-
 t/test-lib.sh                        |   6 +
 17 files changed, 698 insertions(+), 8 deletions(-)
 create mode 100644 Documentation/git-for-each-repo.txt
 create mode 100644 builtin/for-each-repo.c
 create mode 100644 t/helper/test-crontab.c
 create mode 100755 t/t0068-for-each-repo.sh


base-commit: e576ac2c7c7f6c7aa5ac08a516baeb61bf723596
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-724%2Fderrickstolee%2Fmaintenance%2Fscheduled-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-724/derrickstolee/maintenance/scheduled-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/724
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