gc: handle a corner case in gc.bigPackThreshold

[thirdparty/git.git] / Documentation / git-gc.txt

git-gc(1)
=========

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


SYNOPSIS
--------
[verse]
'git gc' [--aggressive] [--auto] [--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.

Users are encouraged to run this task on a regular basis within
each repository to maintain good disk space utilization and good
operating performance.

Some git commands may automatically run 'git gc'; see the `--auto` flag
below for details. If you know what you're doing and all you want is to
disable this behavior permanently without further considerations, just do:

----------------------
$ git config --global gc.auto 0
----------------------

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
	persistent, so this option only needs to be used occasionally; every
	few hundred changesets or so.

--auto::
	With this option, 'git gc' checks whether any housekeeping is
	required; if not, it exits without performing any work.
	Some git commands run `git gc --auto` after performing
	operations that could create many loose objects. Housekeeping
	is required if there are too many loose objects or too many
	packs in the repository.
+
If the number of loose objects exceeds the value of the `gc.auto`
configuration variable, then all loose objects are combined into a
single pack using `git repack -d -l`.  Setting the value of `gc.auto`
to 0 disables automatic packing of loose objects.
+
If the number of packs exceeds the value of `gc.autoPackLimit`,
then existing packs (except those marked with a `.keep` file
or over `gc.bigPackThreshold` limit)
are consolidated into a single pack by using the `-A` option of
'git repack'. Setting `gc.autoPackLimit` to 0 disables
automatic consolidation of packs.
+
If houskeeping is required due to many loose objects or packs, all
other housekeeping tasks (e.g. rerere, working trees, reflog...) will
be performed as well.


--prune=<date>::
	Prune loose objects older than date (default is 2 weeks ago,
	overridable by the config variable `gc.pruneExpire`).
	--prune=all 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 pack and those marked with a
	`.keep` files are consolidated into a single pack. When this
	option is used, `gc.bigPackThreshold` is ignored.

Configuration
-------------

The optional configuration variable `gc.reflogExpire` can be
set to indicate how long historical entries within each branch's
reflog should remain available in this repository.  The setting is
expressed as a length of time, for example '90 days' or '3 months'.
It defaults to '90 days'.

The optional configuration variable `gc.reflogExpireUnreachable`
can be set to indicate how long historical reflog entries which
are not part of the current branch should remain available in
this repository.  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.  This option defaults to '30 days'.

The above two configuration variables can be given to a pattern.  For
example, this sets non-default expiry values only to remote-tracking
branches:

------------
[gc "refs/remotes/*"]
	reflogExpire = never
	reflogExpireUnreachable = 3 days
------------

The optional configuration variable `gc.rerereResolved` indicates
how long records of conflicted merge you resolved earlier are
kept.  This defaults to 60 days.

The optional configuration variable `gc.rerereUnresolved` indicates
how long records of conflicted merge you have not resolved are
kept.  This defaults to 15 days.

The optional configuration variable `gc.packRefs` determines if
'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.
This defaults to true.

The optional configuration variable `gc.aggressiveWindow` controls how
much time is spent optimizing the delta compression of the objects in
the repository when the --aggressive option is specified.  The larger
the value, the more time is spent optimizing the delta compression.  See
the documentation for the --window' option in linkgit:git-repack[1] for
more details.  This defaults to 250.

Similarly, the optional configuration variable `gc.aggressiveDepth`
controls --depth option in linkgit:git-repack[1]. This defaults to 50.

The optional configuration variable `gc.pruneExpire` controls how old
the unreferenced loose objects have to be before they are pruned.  The
default is "2 weeks ago".

Optional configuration variable `gc.worktreePruneExpire` controls how
old a stale working tree should be before `git worktree prune` deletes
it. Default is "3 months ago".


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, refs saved by 'git filter-branch' in
refs/original/, or reflogs (which may reference commits in branches
that were later amended or rewound).
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:

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

. 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) unless they turn off automatic garbage
collection with 'git config gc.auto 0'.

HOOKS
-----

The 'git gc --auto' command will run the 'pre-auto-gc' hook.  See
linkgit:githooks[5] for more information.


SEE ALSO
--------
linkgit:git-prune[1]
linkgit:git-reflog[1]
linkgit:git-repack[1]
linkgit:git-rerere[1]

GIT
---
Part of the linkgit:git[1] suite