From: Patrick Steinhardt <ps@pks.im>
Date: Wed, 25 Aug 2021 14:10:25 GMT
Subject: Re: [PATCH] ls-refs: reuse buffer when sending refs
Message-ID: <YSZPUYk5J10DID+7@ncase>
In-Reply-To: <ccd03e685af0f5cf25c68272a758fc88d115e37a.1629899211.git.ps@pks.im>

On Wed, Aug 25, 2021 at 03:49:51PM +0200, Patrick Steinhardt wrote:
> In the initial reference advertisement, the Git server will first
> announce all of its references to the client. The logic is handled in
> `send_ref()`, which will allocate a new buffer for each refline it is
> about to send. This is quite wasteful: instead of allocating a new
> buffer each time, we can just reuse a buffer.
> 
> Improve this by passing in a buffer via the `ls_refs_data` struct which
> is then reused on each reference. In a repository with about 2.3M refs,
> this speeds up local mirror fetches by about 2%:
> 
>     Benchmark #1: HEAD~: git-fetch
>       Time (mean ± σ):     25.415 s ±  0.131 s    [User: 22.722 s, System: 4.740 s]
>       Range (min … max):   25.240 s … 25.543 s    5 runs
> 
>     Benchmark #2: HEAD: git-fetch
>       Time (mean ± σ):     24.922 s ±  0.110 s    [User: 22.404 s, System: 4.476 s]
>       Range (min … max):   24.825 s … 25.081 s    5 runs
> 
>     Summary
>       'HEAD: git-fetch' ran
>         1.02 ± 0.01 times faster than 'HEAD~: git-fetch'
> 
> Signed-off-by: Patrick Steinhardt <ps@kps.im>

I accidentally mis-typed my mail here. Really shows I should be using
`--signoff` instead of manually signing things. Anyway, I'll fix this in
case I'll need to re-roll.

Patrick