On Fri, Aug 20, 2021 at 10:18:22AM -0700, Junio C Hamano wrote:
> Derrick Stolee <stolee@xxxxxxxxx> writes:
>
> > I do worry about the case where annotated tags greatly outnumber
> > branches, so this binary search is extra overhead and the performance
> > may degrade. Would it be worth checking the ref to see if it lies
> > within "refs/heads/" (or even _not_ in "refs/tags/") before doing
> > this commit-graph check?
>
> Ah, clever.
Good idea. Benchmarks for my test repository (which definitely isn't
representative, but it's at least some numbers) show that restricting to
"refs/heads/" diminishes almost all the gains, while restricting to
everything but "refs/tags/" performs almost the same (it's a tiny bit
slower, probably because of the added string comparisons):
Benchmark #1: all refs: git-fetch
Time (mean ± σ): 32.959 s ± 0.282 s [User: 29.801 s, System: 5.137 s]
Range (min … max): 32.760 s … 33.158 s 2 runs
Benchmark #2: refs/heads: git-fetch
Time (mean ± σ): 56.955 s ± 0.002 s [User: 53.447 s, System: 5.362 s]
Range (min … max): 56.953 s … 56.957 s 2 runs
Benchmark #3: !refs/tags: git-fetch
Time (mean ± σ): 33.447 s ± 0.003 s [User: 30.160 s, System: 5.027 s]
Range (min … max): 33.444 s … 33.449 s 2 runs
Summary
'all refs: git-fetch' ran
1.01 ± 0.01 times faster than '!refs/tags: git-fetch'
1.73 ± 0.01 times faster than 'refs/heads: git-fetch'
This is easily explained by the fact that the test repo has most of its
refs neither in "refs/tags/" nor in "refs/heads/", but rather in special
namespaces like "refs/merge-requests/", "refs/environments/" or
"refs/keep-around/".
I like the idea of excluding "refs/tags/" though: as you point out,
chances are high that these don't point to commits but to annotated tags
instead. So I'll go with that, thanks!
Patrick
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