Re: Performance issue of 'git branch'

[Linus Torvalds <torvalds@linux-foundation.org>]

On Wed, 22 Jul 2009, Linus Torvalds wrote:
> 
> Try this:
> 
> 	git pack-refs --all
> 
> 	rmdir .git/refs/heads
> 	rmdir .git/refs/tags
> 
> 	mkdir .git/refs/heads
> 	mkdir .git/refs/tags
> 
> and see if it magically speeds up.

In fact, you could also just try

	mv .git/refs .git/temp-refs &&
	cp -a .git/temp-refs .git/refs &&
	rm -rf .git/temp-refs

which will re-create other subdirectories too (like .git/refs/remotes 
etc).

Of course, depending on your particular filesystem, a better fix might be 
to enable filename hashing, which gets rid of the whole "look through all 
the old empty stale directory entries to see if there's a filename there" 
issue. That won't fix 'readdir()' performance, but it should fix your 
insane 4-second lstat() thing.

If you have ext3, you'd do something like

	tune2fs -O dir_index /dev/<node-of-your-filesystem-goes-here>

but as mentioned, even with directory indexing it can actually make sense 
to recreate directories that at some point _used_ to be large, but got 
shrunk down to something much smaller. It's a generic directory problem 
(not just ext3, not just unix, it's a common issue across filesystems. 
It's not _universal_ - some smarter filesystems really do shrink their 
directories - but it's certainly not unusual).

		Linus