How often should you use git-gc?

Question

How often should you use git-gc?

The manual page simply says:

Users are encouraged to run this task on a regular basis within each repository to maintain good disk space utilization and good operating performance.

Are there some commands to get some object counts to find out whether it's time to gc?

Answer 1

Note that the downside of garbage-collecting your repository is that, well, the garbage gets collected. As we all know as computer users, files we consider garbage right now might turn out to be very valuable three days in the future. The fact that git keeps most of its debris around has saved my bacon several times – by browsing all the dangling commits, I have recovered much work that I had accidentally canned.

So don’t be too much of a neat freak in your private clones. There’s little need for it.

OTOH, the value of data recoverability is questionable for repos used mainly as remotes, eg. the place all the devs push to and/or pulled from. There, it might be sensible to kick off a GC run and a repacking frequently.

Answer 2

Recent versions of git run gc automatically when required, so you shouldn't have to do anything. See the Options section of man git-gc(1): "Some git commands run git gc --auto after performing operations that could create many loose objects."

Answer 3

You can do it without any interruption, with the new (Git 2.0 Q2 2014) setting gc.autodetach.

See commit 4c4ac4d and commit 9f673f9 (Nguyễn Thái Ngọc Duy, aka pclouds):

gc --auto takes time and can block the user temporarily (but not any less annoyingly).
Make it run in background on systems that support it.
The only thing lost with running in background is printouts. But gc output is not really interesting.
You can keep it in foreground by changing gc.autodetach.

---

Since that 2.0 release, there was a bug though: git 2.7 (Q4 2015) will make sure to not lose the error message.
See commit 329e6e8 (19 Sep 2015) by Nguyễn Thái Ngọc Duy (pclouds).
^{(Merged by Junio C Hamano -- gitster -- in commit 076c827, 15 Oct 2015)}

gc: save log from daemonized gc --auto and print it next time

While commit 9f673f9 (gc: config option for running --auto in background - 2014-02-08) helps reduce some complaints about 'gc --auto' hogging the terminal, it creates another set of problems.

The latest in this set is, as the result of daemonizing, stderr is closed and all warnings are lost. This warning at the end of cmd_gc() is particularly important because it tells the user how to avoid "gc --auto" running repeatedly.
Because stderr is closed, the user does not know, naturally they complain about 'gc --auto' wasting CPU.

Daemonized gc now saves stderr to $GIT_DIR/gc.log.
Following gc --auto will not run and gc.log printed out until the user removes gc.log.