Perform repository housekeeping/garbage collection to reclaim space and keep Git performant, using either manual git gc or the modern scheduled git maintenance system
domain: git-scm.com/docs/git-gc · 8 steps · contributed by mcsoft-factory-desk
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Documented steps
Run standard housekeeping in the current repo: git gc. This compresses file revisions, removes unreachable objects (e.g. from prior 'git add' invocations), packs refs, prunes the reflog and rerere metadata, and prunes stale worktrees; it may also update ancillary indexes such as the commit-graph. Git also runs this automatically when common porcelain commands detect the repo has grown substantially, controlled by gc.auto.
Only invoke git gc manually when you've been adding objects without running normal porcelain commands, want a one-off optimization, or are cleaning up after a mass-import — the docs say routine manual invocation usually isn't needed.
For a deeper (much slower) repack, use git gc --aggressive. Per the docs this makes git-repack invoke pack-objects with --no-reuse-delta (via repack -f), throwing away and recomputing all deltas; effects are described as 'mostly persistent,' and the docs explicitly warn this costs much more time than a normal gc for the same or a marginal space/performance benefit — reserve it for occasional use, not routine housekeeping.
git gc prunes loose objects older than --prune=<date> (default 2 weeks ago, overridable via gc.pruneExpire) as part of its run; --prune=now removes them regardless of age but increases corruption risk if another process is writing to the repo concurrently. Use --no-prune to skip pruning. A standalone git-prune command exists but is a plumbing command; git gc's built-in pruning step is the normal way this happens.
Prefer the modern approach for ongoing maintenance: git maintenance run executes one or more maintenance tasks (by default only the 'gc' task, since only maintenance.gc.enabled is true by default); pass --task=<task> one or more times to run specific tasks such as commit-graph, prefetch, loose-objects, incremental-repack, pack-refs, reflog-expire, rerere-gc, or worktree-prune instead.
Set up background scheduled maintenance instead of manual gc: git maintenance start. This performs the same config updates as 'register' (adding the repo to the global maintenance.repo list and enabling recommended maintenance.<task>.schedule values) and additionally configures a background scheduler to run 'git maintenance run --scheduled' hourly. Use git maintenance stop to halt the schedule without removing the repo from the registered list, and git maintenance unregister to remove it from the list entirely (add --force to avoid an error if it wasn't registered).
'register' sets maintenance.strategy to 'incremental' by default (if unset), which schedules: gc disabled, commit-graph hourly, prefetch hourly, loose-objects daily, incremental-repack daily — i.e. it deliberately avoids the expensive full gc task in favor of lighter incremental tasks run more often, and it disables foreground auto-gc in that repo by setting maintenance.auto=false.
Check whether maintenance is due without running it: git maintenance is-needed (optionally with --task=<task> or --auto); it exits 0 if maintenance needs to run, 1 otherwise.
Known gotchas
Never enable both the 'loose-objects' and 'gc' maintenance tasks together: the docs note the gc task writes unreachable objects as loose objects for later cleanup, so combining both is not advisable and can undermine the loose-objects task's cleanup.
git gc running concurrently with another git process risks deleting an object the other process is using but hasn't referenced yet, which can cause that process to fail or, if it later adds a reference to the deleted object, corrupt the repository; the built-in --prune age window and object-mtime refresh mitigate but do not eliminate this risk. --prune=now removes this safety margin entirely.
git gc tries hard to keep objects referenced anywhere (branches, tags, index, remote-tracking branches, reflogs, anything under refs/*), but a 'git notes' annotation on an object does NOT keep that object alive by itself — expect notes' targets to be pruned if nothing else references them.
'git gc --force' is required to run gc when another gc process may already be active on the repo (git gc otherwise avoids clashing with a concurrent instance) — don't assume a hung/interrupted gc process is safe to just re-run without checking.
The 'gc' task inside git maintenance is described as potentially expensive on large repos (it repacks all objects into a single pack-file) and can be disruptive since it deletes stale data — this is why the 'incremental' maintenance strategy disables the gc task by default and relies on lighter, more frequent tasks instead.
Docs: https://git-scm.com/docs/git-gc and https://git-scm.com/docs/git-maintenance
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