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Date: Wed, 29 Nov 2023 17:25:24 -0500
From: Taylor Blau <me@ttaylorr.com>
To: Patrick Steinhardt <ps@pks.im>
Cc: git@vger.kernel.org
Subject: Re: [PATCH 08/10] t5401: speed up creation of many branches
Message-ID: <ZWe6VDZqW8zCzMNJ@nand.local>
References: <cover.1701242407.git.ps@pks.im>
 <f674119c7801e355cd08a651450abd67947d7456.1701242407.git.ps@pks.im>
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In-Reply-To: <f674119c7801e355cd08a651450abd67947d7456.1701242407.git.ps@pks.im>

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