git gc Command: Repack Repos in CI

git gc packs loose objects and prunes unreachable ones to reduce repo size and speed up operations.

On runners that cache a clone across many builds, the .git directory accumulates loose objects. Running gc periodically keeps the cached repo lean and fast to fetch.

Common flags

• --auto - run gc only if the repo has crossed internal thresholds (cheap to call)
• --prune=<date> - prune unreachable objects older than the given date (e.g. now)
• --aggressive - repack more thoroughly at higher CPU cost
• --no-cruft - write pruned objects loose instead of in a cruft pack
• --quiet / -q - suppress progress output

Example

# Keep a cached CI checkout compact between builds
git gc --auto --prune=now

In CI

Use git gc --auto in cache-restore steps: it is nearly free when nothing is needed and only repacks when the repo has grown. Avoid --aggressive in CI unless disk size is critical, since it is CPU-heavy. Ephemeral runners rarely need gc at all.

Key takeaways

• git gc --auto is a cheap no-op unless the repo actually needs repacking.
• --prune=now reclaims space from unreachable objects in cached checkouts.
• Skip --aggressive in CI; its CPU cost rarely pays off on disposable runners.

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