How Does Git GC Work?

When you run git gc, Git performs several tasks:

1. Pruning: Git removes loose objects that are no longer reachable from any commit or reference. These objects can include commits, trees, and blobs.
2. Repacking: Git repacks all reachable objects into a pack file, which is a compressed file format that stores multiple objects together. This helps in reducing the disk space usage.
3. Removing Old Data: Git deletes old and unnecessary pack files, logs, and other temporary files.

Git gc checks numerous git config settings before running. These values will aid in the understanding of the rest of git gc’s responsibilities.

Git gc config:

gc.reflogExpire

This is an optional variable with a default value of 90 days. It is used to specify the length of time records in a branch’s reflog should be kept.

gc.reflogExpireUnreachable

This is an optional variable with a default value of 30 days. It is used to specify the length of time inaccessible reflog records should be kept.

gc.aggressiveWindow

This is an optional variable with a default value of 250. When git gc is run with the —aggressive option, it determines how much time is spent in the delta compression phase of object packing. Because this can take longer than expected, the impacts of assertive command are typically long-lasting.

gc.aggressiveDepth

Optional variable with a value of 50 by default. It specifies the compression depth used by git-repack during a git gc —aggressive command.

gc.pruneExpire

This setting is optional and defaults to “2 weeks ago.” It determines how long an inaccessible item will be kept before being pruned.

gc.worktreePruneExpire

This setting is optional and defaults to “3 months ago.” It specifies the amount of time a stale functioning tree will be kept before being removed.

git gc exec:

Git gc really runs a bunch of different private subcommands like git prune, git repack, git pack, and git reference behind the scenes. These commands’ increased responsibility is to find any Git items which are outside of the git gc configuration’s standard limits. These items are then compressed or trimmed as needed once they have been located.

Git is a distributed version control system that efficiently handles projects of all sizes. However, over time, a Git repository can accumulate a lot of unnecessary data such as loose objects, unreachable commits, and more. To manage this data, Git employs a garbage collection mechanism, git gc, which cleans up and optimizes the repository. This article explores what Git garbage collection is, how it works, and how to use it effectively.