Re: git slow unless piped to cat

From: Jeff King <peff@peff.net>
Date: Aug 27, 2019, 18:59 UTC
Message-ID: <20190827185929.GA3150@sigill.intra.peff.net>
In-Reply-To: <20190827100427.u3a5uvmylm5vddn2@pengutronix.de>

On Tue, Aug 27, 2019 at 12:04:27PM +0200, Uwe Kleine-König wrote:

Show 11 quoted lines

> 	$ sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"; time env GIT_CONFIG_NOSYSTEM=1 HOME=/nonexistant XDG_CONFIG_HOME=/nonexistant git --no-pager show --no-color --no-decorate v5.2
> 	...
> 
> 	real	0m1.041s
> 	user	0m0.000s
> 	sys	0m0.021s
> 
> 	$ git for-each-ref |wc -l
> 	10013
> 
> So this is indeed the problem.

That's not that many refs. Are they mostly unpacked? Loose refs are awful on a cold cache, since it's one inode per ref (or worse, since it has walk the directories, too).

Try:

  find .git/refs -type f | wc -l

to see the loose ones. If there are a lot, try:

  git pack-refs --prune --all

(or just "git gc", which does this).

Modern versions of Git should delete any leftover empty directories after pruning the loose variants, but I think won't go out of their way to remove ones they didn't delete from. And those are still expensive to walk on a cold cache. If it's still slow, try:

  find .git/refs/* -type d | xargs rmdir -v

-Peff