Git GC Configuration, Notes, and Hooks

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 ------------- include::includes/cmd-config-section-all.adoc[] include::config/gc.adoc[] 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: . 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). 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

The git-gc command has various configuration options and behaviors to manage repository optimization, including the --aggressive option and settings for delta compression. Additionally, git-gc tries to avoid deleting referenced objects and has features to mitigate concurrent process corruption risks, and it also runs hooks like 'pre-auto-gc' to allow for custom actions.