Skip to content

Files

Latest commit

 

History

History
185 lines (148 loc) · 6.57 KB

git-gc.adoc

File metadata and controls

185 lines (148 loc) · 6.57 KB

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 linkgit: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 linkgit:git-repack[1] for more.

--expire-to=<dir>

When packing unreachable objects into a cruft pack, write a cruft pack containing pruned objects (if any) to the directory <dir>. This option only has an effect when used together with --cruft. See the --expire-to option of linkgit:git-repack[1] for more information.

--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, linkgit:git-repack[1] will be invoked with the -f flag, which in turn will pass --no-reuse-delta to linkgit: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 linkgit: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

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 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