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List: git
Subject: Re: [PATCH 08/10] t5401: speed up creation of many branches
From: Taylor Blau <me () ttaylorr ! com>
Date: 2023-11-29 22:25:24
Message-ID: ZWe6VDZqW8zCzMNJ () nand ! local
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On Wed, Nov 29, 2023 at 08:25:09AM +0100, Patrick Steinhardt wrote:
> One of the tests in t5401 creates a bunch of branches by calling
> git-branch(1) for every one of them. This is quite inefficient and takes
> a comparatively long time even on Unix systems where spawning processes
> is comparatively fast. Refactor it to instead use git-update-ref(1),
> which leads to an almost 10-fold speedup:
>
> ```
> Benchmark 1: ./t5401-update-hooks.sh (rev = HEAD)
> Time (mean ± σ): 983.2 ms ± 97.6 ms [User: 328.8 ms, System: 679.2 ms]
> Range (min … max): 882.9 ms … 1078.0 ms 3 runs
>
> Benchmark 2: ./t5401-update-hooks.sh (rev = HEAD~)
> Time (mean ± σ): 9.312 s ± 0.398 s [User: 2.766 s, System: 6.617 s]
> Range (min … max): 8.885 s … 9.674 s 3 runs
>
> Summary
> ./t5401-update-hooks.sh (rev = HEAD) ran
> 9.47 ± 1.02 times faster than ./t5401-update-hooks.sh (rev = HEAD~)
Very nice ;-).
> diff --git a/t/t5401-update-hooks.sh b/t/t5401-update-hooks.sh
> index 001b7a17ad..8b8bc47dc0 100755
> --- a/t/t5401-update-hooks.sh
> +++ b/t/t5401-update-hooks.sh
> @@ -133,10 +133,8 @@ test_expect_success 'pre-receive hook that forgets to read its input' '
> EOF
> rm -f victim.git/hooks/update victim.git/hooks/post-update &&
>
> - for v in $(test_seq 100 999)
> - do
> - git branch branch_$v main || return
> - done &&
> + printf "create refs/heads/branch_%d main\n" $(test_seq 100 999) >input &&
> + git update-ref --stdin <input &&
Not that it really matters here, but you could pipe the output of your
printf directly into git update-ref. I don't think we rely on the value
of "input" after this point, and git is on the right-hand side of the
pipe, so this is safe to do.
But it doesn't matter much either way, just something I noticed while
reading.
Thanks,
Taylor
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