GIT-GC(1) Git Manual GIT-GC(1)

NAME

git-gc - Cleanup unnecessary files and optimize the local repository

SYNOPSIS

git gc [--aggressive] [--auto] [--[no-]detach] [--quiet] [--prune=<date> | --no-prune] [--force] [--keep-largest-pack]

DESCRIPTION

Runs a number of housekeeping tasks within the current repository,
such as compressing file revisions (to reduce disk space and increase
performance), removing unreachable objects which may have been
created from prior invocations of git add, packing refs, pruning
reflog, rerere metadata or stale working trees. May also update
ancillary indexes such as the commit-graph.

When common porcelain operations that create objects are run, they
will check whether the repository has grown substantially since the
last maintenance, and if so run git gc automatically. See gc.auto
below for how to disable this behavior.

Running git gc manually should only be needed when adding objects to
a repository without regularly running such porcelain commands, to do
a one-off repository optimization, or e.g. to clean up a suboptimal
mass-import. See the "PACKFILE OPTIMIZATION" section in git-fast-
import(1) for more details on the import case.

OPTIONS

--aggressive
Usually git gc runs very quickly while providing good disk space
utilization and performance. This option will cause git gc to
more aggressively optimize the repository at the expense of
taking much more time. The effects of this optimization are
mostly persistent. See the "AGGRESSIVE" section below for
details.

--auto
With this option, git gc checks whether any housekeeping is
required; if not, it exits without performing any work.

See the gc.auto option in the "CONFIGURATION" section below for
how this heuristic works.

Once housekeeping is triggered by exceeding the limits of
configuration options such as gc.auto and gc.autoPackLimit, all
other housekeeping tasks (e.g. rerere, working trees, reflog...)
will be performed as well.

--[no-]detach
Run in the background if the system supports it. This option
overrides the gc.autoDetach config.

--[no-]cruft
When expiring unreachable objects, pack them separately into a
cruft pack instead of storing them as loose objects. --cruft is
on by default.

--max-cruft-size=<n>
When packing unreachable objects into a cruft pack, limit the
size of new cruft packs to be at most <n> bytes. Overrides any
value specified via the gc.maxCruftSize configuration. See the
--max-cruft-size option of git-repack(1) for more.

--prune=<date>
Prune loose objects older than date (default is 2 weeks ago,
overridable by the config variable gc.pruneExpire). --prune=now
prunes loose objects regardless of their age and increases the
risk of corruption if another process is writing to the
repository concurrently; see "NOTES" below. --prune is on by
default.

--no-prune
Do not prune any loose objects.

--quiet
Suppress all progress reports.

--force
Force git gc to run even if there may be another git gc instance
running on this repository.

--keep-largest-pack
All packs except the largest non-cruft pack, any packs marked
with a .keep file, and any cruft pack(s) are consolidated into a
single pack. When this option is used, gc.bigPackThreshold is
ignored.

AGGRESSIVE

When the --aggressive option is supplied, git-repack(1) will be
invoked with the -f flag, which in turn will pass --no-reuse-delta to
git-pack-objects(1). This will throw away any existing deltas and
re-compute them, at the expense of spending much more time on the
repacking.

The effects of this are mostly persistent, e.g. when packs and loose
objects are coalesced into one another pack the existing deltas in
that pack might get re-used, but there are also various cases where
we might pick a sub-optimal delta from a newer pack instead.

Furthermore, supplying --aggressive will tweak the --depth and
--window options passed to git-repack(1). See the gc.aggressiveDepth
and gc.aggressiveWindow settings below. By using a larger window size
we're more likely to find more optimal deltas.

It's probably not worth it to use this option on a given repository
without running tailored performance benchmarks on it. It takes a lot
more time, and the resulting space/delta optimization may or may not
be worth it. Not using this at all is the right trade-off for most
users and their repositories.

CONFIGURATION

Everything below this line in this section is selectively included
from the git-config(1) documentation. The content is the same as
what's found there:

gc.aggressiveDepth
The depth parameter used in the delta compression algorithm used
by git gc --aggressive. This defaults to 50, which is the default
for the --depth option when --aggressive isn't in use.

See the documentation for the --depth option in git-repack(1) for
more details.

gc.aggressiveWindow
The window size parameter used in the delta compression algorithm
used by git gc --aggressive. This defaults to 250, which is a
much more aggressive window size than the default --window of 10.

See the documentation for the --window option in git-repack(1)
for more details.

gc.auto
When there are approximately more than this many loose objects in
the repository, git gc --auto will pack them. Some Porcelain
commands use this command to perform a light-weight garbage
collection from time to time. The default value is 6700.

Setting this to 0 disables not only automatic packing based on
the number of loose objects, but also any other heuristic git gc
--auto will otherwise use to determine if there's work to do,
such as gc.autoPackLimit.

gc.autoPackLimit
When there are more than this many packs that are not marked with
*.keep file in the repository, git gc --auto consolidates them
into one larger pack. The default value is 50. Setting this to 0
disables it. Setting gc.auto to 0 will also disable this.

See the gc.bigPackThreshold configuration variable below. When in
use, it'll affect how the auto pack limit works.

gc.autoDetach
Make git gc --auto return immediately and run in the background
if the system supports it. Default is true. This config variable
acts as a fallback in case maintenance.autoDetach is not set.

gc.bigPackThreshold
If non-zero, all non-cruft packs larger than this limit are kept
when git gc is run. This is very similar to --keep-largest-pack
except that all non-cruft packs that meet the threshold are kept,
not just the largest pack. Defaults to zero. Common unit suffixes
of k, m, or g are supported.

Note that if the number of kept packs is more than
gc.autoPackLimit, this configuration variable is ignored, all
packs except the base pack will be repacked. After this the
number of packs should go below gc.autoPackLimit and
gc.bigPackThreshold should be respected again.

If the amount of memory estimated for git repack to run smoothly
is not available and gc.bigPackThreshold is not set, the largest
pack will also be excluded (this is the equivalent of running git
gc with --keep-largest-pack).

gc.writeCommitGraph
If true, then gc will rewrite the commit-graph file when git-
gc(1) is run. When using git gc --auto the commit-graph will be
updated if housekeeping is required. Default is true. See git-
commit-graph(1) for details.

gc.logExpiry
If the file gc.log exists, then git gc --auto will print its
content and exit with status zero instead of running unless that
file is more than gc.logExpiry old. Default is "1.day". See
gc.pruneExpire for more ways to specify its value.

gc.packRefs
Running git pack-refs in a repository renders it unclonable by
Git versions prior to 1.5.1.2 over dumb transports such as HTTP.
This variable determines whether git gc runs git pack-refs. This
can be set to notbare to enable it within all non-bare repos or
it can be set to a boolean value. The default is true.

gc.cruftPacks
Store unreachable objects in a cruft pack (see git-repack(1))
instead of as loose objects. The default is true.

gc.maxCruftSize
Limit the size of new cruft packs when repacking. When specified
in addition to --max-cruft-size, the command line option takes
priority. See the --max-cruft-size option of git-repack(1).

gc.pruneExpire
When git gc is run, it will call prune --expire 2.weeks.ago (and
repack --cruft --cruft-expiration 2.weeks.ago if using cruft
packs via gc.cruftPacks or --cruft). Override the grace period
with this config variable. The value "now" may be used to disable
this grace period and always prune unreachable objects
immediately, or "never" may be used to suppress pruning. This
feature helps prevent corruption when git gc runs concurrently
with another process writing to the repository; see the "NOTES"
section of git-gc(1).

gc.worktreePruneExpire
When git gc is run, it calls git worktree prune --expire
3.months.ago. This config variable can be used to set a different
grace period. The value "now" may be used to disable the grace
period and prune $GIT_DIR/worktrees immediately, or "never" may
be used to suppress pruning.

gc.reflogExpire, gc.<pattern>.reflogExpire
git reflog expire removes reflog entries older than this time;
defaults to 90 days. The value "now" expires all entries
immediately, and "never" suppresses expiration altogether. With
"<pattern>" (e.g. "refs/stash") in the middle the setting applies
only to the refs that match the <pattern>.

gc.reflogExpireUnreachable, gc.<pattern>.reflogExpireUnreachable
git reflog expire removes reflog entries older than this time and
are not reachable from the current tip; defaults to 30 days. The
value "now" expires all entries immediately, and "never"
suppresses expiration altogether. With "<pattern>" (e.g.
"refs/stash") in the middle, the setting applies only to the refs
that match the <pattern>.

These types of entries are generally created as a result of using
git commit --amend or git rebase and are the commits prior to the
amend or rebase occurring. Since these changes are not part of
the current project most users will want to expire them sooner,
which is why the default is more aggressive than gc.reflogExpire.

gc.recentObjectsHook
When considering whether or not to remove an object (either when
generating a cruft pack or storing unreachable objects as loose),
use the shell to execute the specified command(s). Interpret
their output as object IDs which Git will consider as "recent",
regardless of their age. By treating their mtimes as "now", any
objects (and their descendants) mentioned in the output will be
kept regardless of their true age.

Output must contain exactly one hex object ID per line, and
nothing else. Objects which cannot be found in the repository are
ignored. Multiple hooks are supported, but all must exit
successfully, else the operation (either generating a cruft pack
or unpacking unreachable objects) will be halted.

gc.repackFilter
When repacking, use the specified filter to move certain objects
into a separate packfile. See the --filter=<filter-spec> option
of git-repack(1).

gc.repackFilterTo
When repacking and using a filter, see gc.repackFilter, the
specified location will be used to create the packfile containing
the filtered out objects. WARNING: The specified location should
be accessible, using for example the Git alternates mechanism,
otherwise the repo could be considered corrupt by Git as it might
not be able to access the objects in that packfile. See the
--filter-to=<dir> option of git-repack(1) and the
objects/info/alternates section of gitrepository-layout(5).

gc.rerereResolved
Records of conflicted merge you resolved earlier are kept for
this many days when git rerere gc is run. You can also use more
human-readable "1.month.ago", etc. The default is 60 days. See
git-rerere(1).

gc.rerereUnresolved
Records of conflicted merge you have not resolved are kept for
this many days when git rerere gc is run. You can also use more
human-readable "1.month.ago", etc. The default is 15 days. See
git-rerere(1).

NOTES

git gc tries very hard not to delete objects that are referenced
anywhere in your repository. In particular, it will keep not only
objects referenced by your current set of branches and tags, but also
objects referenced by the index, remote-tracking branches, reflogs
(which may reference commits in branches that were later amended or
rewound), and anything else in the refs/* namespace. Note that a note
(of the kind created by git notes) attached to an object does not
contribute in keeping the object alive. If you are expecting some
objects to be deleted and they aren't, check all of those locations
and decide whether it makes sense in your case to remove those
references.

On the other hand, when git gc runs concurrently with another
process, there is a risk of it deleting an object that the other
process is using but hasn't created a reference to. This may just
cause the other process to fail or may corrupt the repository if the
other process later adds a reference to the deleted object. Git has
two features that significantly mitigate this problem:

1. Any object with modification time newer than the --prune date is
kept, along with everything reachable from it.

2. Most operations that add an object to the database update the
modification time of the object if it is already present so that
#1 applies.

However, these features fall short of a complete solution, so users
who run commands concurrently have to live with some risk of
corruption (which seems to be low in practice).

HOOKS

The git gc --auto command will run the pre-auto-gc hook. See
githooks(5) for more information.

SEE ALSO

git-prune(1) git-reflog(1) git-repack(1) git-rerere(1)

GIT

Part of the git(1) suite

Git 2.48.1 2025-01-13 GIT-GC(1)