Re: Possible performance regression in for-each-ref in git 2.40.0
On Wed, Jun 25, 2025, at 13:28, Andrzej Dębski wrote:
Show 43 quoted lines
> One of Dropbox SWEs observed that a specific git command in Go
> language tooling
> https://github.com/golang/go/blob/e515ef8bc271f632bb2ebb94e8e700ab67274268/src/cmd/go/internal/modfetch/codehost/git.go#L758
> took over 20 seconds. Internally we distribute git 2.46.0 right now
> but the SWE had an older version of git around (2.39.5) and observed a
> performance regression between those 2 versions.
>
> We've did some performance measurements and the command like "git
> for-each-ref --format="%(refname)" refs/tags --merged HEAD >
> /dev/null"
> spent majority of time in function "tips_reachable_from_bases"
> introduced in git 2.40.0:
> https://github.com/git/git/commit/cbfe360b140fe92d9c4a763bf630c3b8ba431522
>
> Similar performance degradation can be observed in git 2.50
>
> Given that the command references tags I've experimented and observed
> that the command execution time decreased with the amount of tags I've
> removed from the local copy of the repo.
>
> Context: in Dropbox we operate a large monorepo with around 65K tags
> right now and growing every day.
>
> The question is, given the same command used to be much faster in
> older versions of git is this considered a regression and can be fixed
> in future releases of git?
>
>
> [System Info]
> git version: 2.46.0
> cpu: bazel
> built from commit: bazel
> sizeof-long: 8
> sizeof-size_t: 8
> shell-path: /bin/sh
> libcurl: 7.82.0
> OpenSSL: OpenSSL 1.1.1w 11 Sep 2023
> zlib: 1.2.13
> uname: Linux 6.8.0-1029-aws #31~22.04.1-Ubuntu SMP Thu Apr 24 21:16:18
> UTC 2025 x86_64
> compiler info: gnuc: 11.2
> libc info: glibc: 2.35
> $SHELL (typically, interactive shell): /bin/bash
--
Kristoffer Haugsbakk