When renaming a remote we also need to rename all references
accordingly. But while we only need to rename references that are
contained in the "refs/remotes/$OLDNAME/" namespace, we end up using
`refs_for_each_rawref()` that iterates through _all_ references. We know
to exit early in the callback in case we see an irrelevant reference,
but ultimately this is still a waste of compute as we knowingly iterate
through references that we won't ever care about.
Improve this by using `refs_for_each_rawref_in()`, which knows to only
iterate through (potentially broken) references in a given prefix.
The following benchmark renames a remote with a single reference in a
repository that has 100k unrelated references. This shows a sizeable
improvement with the "files" backend:
Benchmark 1: rename remote (refformat = files, revision = HEAD~)
Time (mean ± σ): 42.6 ms ± 0.9 ms [User: 29.1 ms, System: 8.4 ms]
Range (min … max): 40.1 ms … 43.3 ms 10 runs
Benchmark 2: rename remote (refformat = files, revision = HEAD)
Time (mean ± σ): 31.7 ms ± 4.0 ms [User: 19.6 ms, System: 6.9 ms]
Range (min … max): 27.1 ms … 36.0 ms 10 runs
Summary
rename remote (refformat = files, revision = HEAD) ran
1.35 ± 0.17 times faster than rename remote (refformat = files, revision = HEAD~)
The "reftable" backend shows roughly the same absolute improvement, but
given that it's already significantly faster than the "files" backend
this translates to a much larger relative improvement:
Benchmark 1: rename remote (refformat = reftable, revision = HEAD~)
Time (mean ± σ): 18.2 ms ± 0.5 ms [User: 12.7 ms, System: 3.0 ms]
Range (min … max): 17.3 ms … 21.4 ms 110 runs
Benchmark 2: rename remote (refformat = reftable, revision = HEAD)
Time (mean ± σ): 8.8 ms ± 0.5 ms [User: 3.8 ms, System: 2.9 ms]
Range (min … max): 7.5 ms … 9.9 ms 167 runs
Summary
rename remote (refformat = reftable, revision = HEAD) ran
2.07 ± 0.12 times faster than rename remote (refformat = reftable, revision = HEAD~)
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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