Re: [BUG] "git describe --match" performance

From: Jeff King <peff@peff.net>
Date: Oct 31, 2024, 11:47 UTC
Message-ID: <20241031114731.GA608553@coredump.intra.peff.net>
In-Reply-To: <20241030044322.b5n3ji2n6gaeo5u6@treble.attlocal.net>

On Tue, Oct 29, 2024 at 09:43:22PM -0700, Josh Poimboeuf wrote:

Show 18 quoted lines

> $ time git describe --match=v6.10-rc7 --debug
> describe HEAD
> No exact match on refs or tags, searching to describe
> finished search at d8470b7c13e11c18cf14a7e3180f0b00e715e4f0
>  annotated       1844 v6.10-rc7
> traversed 1282750 commits
> v6.10-rc7-1844-gc61e41121036
> 
> real	0m9.243s
> user	0m8.940s
> sys	0m0.268s
> 
> $ time git describe
> v6.10-rc7-1844-gc61e41121036
> 
> real	0m0.149s
> user	0m0.111s
> sys	0m0.036s

There's more discussion of the actual solution in the nearby thread from Rasmus. But I did want to note one thing here: when I initially tried to reproduce your problem, my "slow" case was a lot less bad.

The reason is that I had a commit graph file to speed up traversal. So independent of the git-describe fix, you might want to try:

  git commit-graph write --reachable

That reduces the slow case for me by a factor of 10. And likewise other traversal operations should get faster.

I think we'll build the commit graph file by default these days when you run "git gc". But we don't build it immediately after cloning. Perhaps we should change that.

-Peff