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![Taylor Blau](/assets/img/avatar_default.png)
Back in5b92477f89
(builtin/gc.c: conditionally avoid pruning objects via loose, 2022-05-20), `git gc` learned the `--cruft` option and `gc.cruftPacks` configuration to opt-in to writing cruft packs when collecting or pruning unreachable objects. Cruft packs were introduced with the merge ina50036da1a
(Merge branch 'tb/cruft-packs', 2022-06-03). They address the problem of "loose object explosions", where Git will write out many individual loose objects when there is a large number of unreachable objects that have not yet aged past `--prune=<date>`. Instead of keeping track of those unreachable yet recent objects via their loose object file's mtime, cruft packs collect all unreachable objects into a single pack with a corresponding `*.mtimes` file that acts as a table to store the mtimes of all unreachable objects. This prevents the need to store unreachable objects as loose as they age out of the repository, and avoids the problem of loose object explosions. Beyond avoiding loose object explosions, cruft packs also act as a more efficient mechanism to store unreachable objects as they age out of a repository. This is because pairs of similar unreachable objects serve as delta bases for one another. In5b92477f89
, the feature was introduced as experimental. Since then, GitHub has been running these patches in every repository generating hundreds of millions of cruft packs along the way. The feature is battle-tested, and avoids many pathological cases such as above. Users who either run `git gc` manually, or via `git maintenance` can benefit from having cruft packs. As such, enable cruft pack generation to take place by default (by making `gc.cruftPacks` have the default of "true" rather than "false). Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
169 lines
5.9 KiB
Plaintext
169 lines
5.9 KiB
Plaintext
git-gc(1)
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=========
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NAME
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----
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git-gc - Cleanup unnecessary files and optimize the local repository
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SYNOPSIS
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--------
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[verse]
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'git gc' [--aggressive] [--auto] [--quiet] [--prune=<date> | --no-prune] [--force] [--keep-largest-pack]
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DESCRIPTION
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-----------
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Runs a number of housekeeping tasks within the current repository,
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such as compressing file revisions (to reduce disk space and increase
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performance), removing unreachable objects which may have been
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created from prior invocations of 'git add', packing refs, pruning
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reflog, rerere metadata or stale working trees. May also update ancillary
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indexes such as the commit-graph.
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When common porcelain operations that create objects are run, they
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will check whether the repository has grown substantially since the
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last maintenance, and if so run `git gc` automatically. See `gc.auto`
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below for how to disable this behavior.
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Running `git gc` manually should only be needed when adding objects to
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a repository without regularly running such porcelain commands, to do
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a one-off repository optimization, or e.g. to clean up a suboptimal
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mass-import. See the "PACKFILE OPTIMIZATION" section in
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linkgit:git-fast-import[1] for more details on the import case.
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OPTIONS
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-------
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--aggressive::
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Usually 'git gc' runs very quickly while providing good disk
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space utilization and performance. This option will cause
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'git gc' to more aggressively optimize the repository at the expense
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of taking much more time. The effects of this optimization are
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mostly persistent. See the "AGGRESSIVE" section below for details.
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--auto::
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With this option, 'git gc' checks whether any housekeeping is
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required; if not, it exits without performing any work.
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+
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See the `gc.auto` option in the "CONFIGURATION" section below for how
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this heuristic works.
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+
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Once housekeeping is triggered by exceeding the limits of
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configuration options such as `gc.auto` and `gc.autoPackLimit`, all
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other housekeeping tasks (e.g. rerere, working trees, reflog...) will
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be performed as well.
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--[no-]cruft::
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When expiring unreachable objects, pack them separately into a
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cruft pack instead of storing them as loose objects. `--cruft`
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is on by default.
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--prune=<date>::
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Prune loose objects older than date (default is 2 weeks ago,
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overridable by the config variable `gc.pruneExpire`).
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--prune=now prunes loose objects regardless of their age and
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increases the risk of corruption if another process is writing to
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the repository concurrently; see "NOTES" below. --prune is on by
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default.
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--no-prune::
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Do not prune any loose objects.
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--quiet::
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Suppress all progress reports.
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--force::
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Force `git gc` to run even if there may be another `git gc`
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instance running on this repository.
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--keep-largest-pack::
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All packs except the largest non-cruft pack, any packs marked
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with a `.keep` file, and any cruft pack(s) are consolidated into
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a single pack. When this option is used, `gc.bigPackThreshold`
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is ignored.
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AGGRESSIVE
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----------
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When the `--aggressive` option is supplied, linkgit:git-repack[1] will
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be invoked with the `-f` flag, which in turn will pass
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`--no-reuse-delta` to linkgit:git-pack-objects[1]. This will throw
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away any existing deltas and re-compute them, at the expense of
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spending much more time on the repacking.
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The effects of this are mostly persistent, e.g. when packs and loose
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objects are coalesced into one another pack the existing deltas in
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that pack might get re-used, but there are also various cases where we
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might pick a sub-optimal delta from a newer pack instead.
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Furthermore, supplying `--aggressive` will tweak the `--depth` and
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`--window` options passed to linkgit:git-repack[1]. See the
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`gc.aggressiveDepth` and `gc.aggressiveWindow` settings below. By
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using a larger window size we're more likely to find more optimal
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deltas.
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It's probably not worth it to use this option on a given repository
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without running tailored performance benchmarks on it. It takes a lot
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more time, and the resulting space/delta optimization may or may not
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be worth it. Not using this at all is the right trade-off for most
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users and their repositories.
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CONFIGURATION
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-------------
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include::includes/cmd-config-section-all.txt[]
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include::config/gc.txt[]
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NOTES
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-----
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'git gc' tries very hard not to delete objects that are referenced
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anywhere in your repository. In particular, it will keep not only
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objects referenced by your current set of branches and tags, but also
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objects referenced by the index, remote-tracking branches, reflogs
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(which may reference commits in branches that were later amended or
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rewound), and anything else in the refs/* namespace. Note that a note
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(of the kind created by 'git notes') attached to an object does not
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contribute in keeping the object alive. If you are expecting some
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objects to be deleted and they aren't, check all of those locations
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and decide whether it makes sense in your case to remove those
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references.
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On the other hand, when 'git gc' runs concurrently with another process,
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there is a risk of it deleting an object that the other process is using
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but hasn't created a reference to. This may just cause the other process
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to fail or may corrupt the repository if the other process later adds a
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reference to the deleted object. Git has two features that significantly
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mitigate this problem:
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. Any object with modification time newer than the `--prune` date is kept,
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along with everything reachable from it.
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. Most operations that add an object to the database update the
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modification time of the object if it is already present so that #1
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applies.
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However, these features fall short of a complete solution, so users who
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run commands concurrently have to live with some risk of corruption (which
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seems to be low in practice).
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HOOKS
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-----
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The 'git gc --auto' command will run the 'pre-auto-gc' hook. See
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linkgit:githooks[5] for more information.
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SEE ALSO
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--------
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linkgit:git-prune[1]
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linkgit:git-reflog[1]
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linkgit:git-repack[1]
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linkgit:git-rerere[1]
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GIT
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---
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Part of the linkgit:git[1] suite
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