On Wed, Feb 09, 2022 at 07:01:54PM +0100, Christian Couder wrote:
> On Mon, Feb 7, 2022 at 7:03 AM Patrick Steinhardt <ps@xxxxxx> wrote:
>
> > Benchmarks in a repository with about 2,1 million refs and an up-to-date
> > commit-graph show a 20% speedup when mirror-fetching:
> >
> > Benchmark 1: git fetch --atomic +refs/*:refs/* (v2.35.0)
> > Time (mean ± σ): 75.264 s ± 1.115 s [User: 68.199 s, System: 10.094 s]
> > Range (min … max): 74.145 s … 76.862 s 5 runs
> >
> > Benchmark 2: git fetch --atomic +refs/*:refs/* (HEAD)
> > Time (mean ± σ): 62.350 s ± 0.854 s [User: 55.412 s, System: 9.976 s]
> > Range (min … max): 61.224 s … 63.216 s 5 runs
> >
> > Summary
> > 'git fetch --atomic +refs/*:refs/* (HEAD)' ran
> > 1.21 ± 0.02 times faster than 'git fetch --atomic +refs/*:refs/* (v2.35.0)'
>
> The commit message and code make sense to me, but I wonder if there is
> a reason why --atomic is used when fetching.
The repository that I was mirror-fetching into needs to update a big
bunch of references, and doing that via `--atomic` is more efficient
than doing it without, and this shows in the benchmark. I did another
benchmarking run without `--atomic`, and it is indeed about 30 seconds
slower for both cases. But interestingly the relative performance
improvement is still roughly the same:
Benchmark 1: git fetch +refs/*:refs/* (v2.35.0)
Time (mean ± σ): 115.587 s ± 2.009 s [User: 109.874 s, System: 11.305 s]
Range (min … max): 113.584 s … 118.820 s 5 runs
Benchmark 2: git fetch +refs/*:refs/* (pks-fetch-pack-optim-v1~)
Time (mean ± σ): 96.859 s ± 0.624 s [User: 91.948 s, System: 10.980 s]
Range (min … max): 96.180 s … 97.875 s 5 runs
Summary
'git fetch +refs/*:refs/* (pks-fetch-pack-optim-v1~)' ran
1.19 ± 0.02 times faster than 'git fetch +refs/*:refs/* (v2.35.0)'
I'll update the commit message to just use this new benchmark so that
the `--atomic` flag doesn't cause any questions.
Patrick
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