git repack

Loose objects in, packfiles out.

🎯 What & why

git repack consolidates loose objects and existing packfiles into fewer, denser packs. It's the heavy lifter that git gc calls under the hood.

🧠 Mental model

Loose objects are one file per object — fast to write, slow to read at scale. Packs are delta-compressed archives with an index. Repack trades CPU now for I/O savings forever.

🛠️ Synopsis

git repack [-a] [-A] [-d] [-l] [-f]
          [--max-pack-size=<n>] [--depth=<n>] [--window=<n>]
          [--keep-pack=<name>] [--write-bitmap-index]

🎚️ Switches & options

Flag	What it does
`-a`	Pack all reachable objects into a single new pack. Without this, you only repack loose objects.
`-A`	Like `-a` but unreachable objects are exploded back to loose instead of dropped — gives `gc` a chance to expire them.
`-d`	Delete redundant packs after repacking. Without `-d` you accumulate cruft.
`-l`	Use only local packs; skip alternates. Important when working with shared object stores.
`--max-pack-size=<n>`	Cap pack file size (e.g. `2g`). Useful for filesystems that hate huge files.
`--depth=<n>`	Max delta chain length. Default 50; larger = smaller packs, slower reads.
`--window=<n>`	How many neighboring objects to consider for delta candidates. Default 10; larger = better compression, slower repack.
`--write-bitmap-index`	Generate a `.bitmap` file. Massive speedup for `clone` and `fetch` on the server side.
`-f`	⚠️ Force re-deltification of all objects. Throws away existing deltas — only use after changing `--depth`/`--window`.

💡 Use cases

Server-side maintenance: nightly repack -adf --write-bitmap-index for clone performance.
Reclaiming disk after a big history rewrite or filter-repo.
Recovering a repo where .git/objects/ has thousands of loose files slowing every command.
Tuning pack size for storage backends that have file-size limits.

🧪 Examples

The standard incantation

git repack -ad

Server-grade repack with bitmaps

git repack -adf --write-bitmap-index --depth=50 --window=250

Local-only, ignore alternates

git repack -adl

Cap pack size at 2GB

git repack -ad --max-pack-size=2g

🎓 Recommendations

-ad is the everyday shortcut: pack everything, drop redundant packs. Memorize it.
On any repo serving clones, --write-bitmap-index is non-negotiable — it can cut clone time by 10x.
Don't run repack while another writer is active; you can race against pushes and end up with dangling refs to repacked objects.

🪤 Common pitfalls

Without -d, your old packs stay around as cruft. Disk usage grows, doesn't shrink.
-A (capital) keeps unreachable objects as loose so gc can expire them; -a (lower) just packs what's reachable. They're not interchangeable.
Cranking --window and --depth for tighter packs costs CPU every read, not just at repack time.

🔗 Related modules

📝 Quiz

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