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-]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.
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 migh 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).
