Re: Performance regression in "update" hooks

From: Adrian Ratiu <adrian.ratiu@collabora.com>
Date: Mar 2, 2026, 13:37 UTC
Message-ID: <87bjh673o0.fsf@gentoo.mail-host-address-is-not-set>
In-Reply-To: <aaU5lZwEuR4OrxCl@pks.im>

On Mon, 02 Mar 2026, Patrick Steinhardt <ps@pks.im> wrote:

Show 28 quoted lines

> Hi,
>
> Bencher has alerted me that there's been two performance regressions in
> git-receive-pack(1) [1] and git-fetch(1) [2].
>
> The first one is quite easy to reproduce with the benchmarks at [3] and
> bisects to fc148b146a (receive-pack: convert update hooks to new API,
> 2026-01-28):
>
>   $ cd receive-refs
>   $ ./run --revisions /path/to/your/git/repo \
>       fc148b146ad41be71a7852c4867f0773cbfe1ff9~,fc148b146ad41be71a7852c4867f0773cbfe1ff9 \
>       --parameter-list refformat reftable \
>       --parameter-list refcount 10000
>
>   Benchmark 1: receive: many refs (refformat = reftable, refcount = 10000, revision = fc148b146ad41be71a7852c4867f0773cbfe1ff9~)
>     Time (mean ± σ):     182.0 ms ±   2.7 ms    [User: 91.5 ms, System: 89.3 ms]
>     Range (min … max):   175.8 ms … 185.0 ms    15 runs
>
>   Benchmark 2: receive: many refs (refformat = reftable, refcount = 10000, revision = fc148b146ad41be71a7852c4867f0773cbfe1ff9)
>     Time (mean ± σ):     484.6 ms ±  27.6 ms    [User: 176.2 ms, System: 376.1 ms]
>     Range (min … max):   406.2 ms … 495.1 ms    10 runs
>
>   Summary
>     receive: many refs (refformat = reftable, refcount = 10000, revision = fc148b146ad41be71a7852c4867f0773cbfe1ff9~) ran
>       2.66 ± 0.16 times faster than receive: many refs (refformat = reftable, refcount = 10000, revision = fc148b146ad41be71a7852c4867f0773cbfe1ff9)
>
> I've Cc'd Adrian.

Hi Patrick,

I looked at the commits before and after the many-refs test regression and it appears the regressions started after Junio landed v2 of the config series in next [1], which might cause it.

v2 was not ready to land. I sent v3 yesterday addressing all the feedback, didn't even realize v2 landed. :)

Does the regression go away if you revert [1] ?

I don't have the benchmark setup and it might be easier for you to confirm?

Many thanks!

1:

commit 6a04cca28e210f0c51cfefcb52475c7ede6e99fb
Merge: d6ebc97cb1 4b12cd3ae3
Author:     Junio C Hamano <gitster@pobox.com>
AuthorDate: Fri Feb 27 15:16:30 2026 -0800
Commit:     Junio C Hamano <gitster@pobox.com>
CommitDate: Fri Feb 27 15:16:30 2026 -0800

    Merge branch 'ar/config-hooks' into next
    
    Allow hook commands to be defined (possibly centrally) in the
    configuration files, and run multiple of them for the same hook
    event.
    
    * ar/config-hooks:
      hook: add -z option to "git hook list"
      hook: allow out-of-repo 'git hook' invocations
      hook: allow event = "" to overwrite previous values
      hook: allow disabling config hooks
      hook: include hooks from the config
      hook: add "git hook list" command
      hook: run a list of hooks to prepare for multihook support
      hook: add internal state alloc/free callbacks