git gc

Clean up dangling objects and recompress packfiles.

🎯 What & why

Garbage-collect unreachable objects, repack loose ones into packfiles, expire reflog entries, prune dangling refs. Keeps the repo small and fast.

🧠 Mental model

GC runs repack (loose → pack), then prune (drops unreachable objects older than the prune horizon), then expires the reflog. Reachability is computed by walking from every ref in refs/. Anything not reachable and older than two weeks (default) is fair game.

🛠️ Synopsis

git gc [--aggressive] [--auto] [--[no-]detach] [--quiet] [--prune=<date> | --no-prune] [--force] [--keep-largest-pack]

🎚️ Switches & options

Flag	What it does
`--auto`	Run only if needed (e.g. too many loose objects).
`--aggressive`	Spend more CPU for better packing. Rarely needed; gc is already good.
`--prune=<date>`	Prune objects older than `<date>` (default: 2 weeks).
`--force`	Run even if another gc is in progress.

💡 Use cases

Repos that have accumulated lots of loose objects.
After heavy filter-repo operations.
Periodic cleanup in long-lived clones.

🧪 Examples

Standard auto-gc.

$ git gc --auto

Aggressive pack (slow).

$ git gc --aggressive

🎓 Recommendations

Let git gc --auto handle most cases. Manual gc is rarely the right tool.
Don't reach for --aggressive reflexively. It rarely helps and takes a long time.

🪤 Common pitfalls

GC won't prune objects newer than the prune horizon (default 2 weeks). Recently 'lost' objects survive.
Reflog is gc's friend — don't disable it unless you understand the implications.

🔗 Related modules

📝 Quiz

Hit each option, then Check answers. Score is recorded; Next is always open.