git-gc - Cleanup unnecessary files and optimize the local repository
git gc [--aggressive] [--auto] [--quiet] [--prune=<date> | --no-prune] [--force] [--keep-largest-pack]
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.
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.
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.
The below documentation is the same as what’s found in git-config(1):
See the documentation for the --depth option in git-repack(1) for more details.
See the documentation for the --window option in git-repack(1) for more details.
Setting this to 0 disables not only automatic packing based on the number of loose objects, but any other heuristic git gc --auto will otherwise use to determine if there’s work to do, such as gc.autoPackLimit.
See the gc.bigPackThreshold configuration variable below. When in use, it’ll affect how the auto pack limit works.
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).
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.
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:
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).
The git gc --auto command will run the pre-auto-gc hook. See githooks(5) for more information.
Part of the git(1) suite