On 6/3/2022 5:55 PM, Taylor Blau wrote:
> When `show-ref` is combined with the `--heads` or `--tags` options, it
> can avoid iterating parts of a repository's references that it doesn't
> care about.
>
> But it doesn't take advantage of this potential optimization. When this
> command was introduced back in 358ddb62cf (Add "git show-ref" builtin
> command, 2006-09-15), `for_each_ref_in()` did exist. But since most
> repositories don't have many (any?) references that aren't branches or
> tags already, this makes little difference in practice.
...
> Nonetheless, in our synthetic example above, this provides a significant
> speed-up ("git" is roughly v2.36, "git.compile" is this patch):
>
> $ hyperfine -N 'git show-ref --heads' 'git.compile show-ref --heads'
> Benchmark 1: git show-ref --heads
> Time (mean ± σ): 49.9 ms ± 6.2 ms [User: 45.6 ms, System: 4.1 ms]
> Range (min … max): 46.1 ms … 73.6 ms 43 runs
>
> Benchmark 2: git.compile show-ref --heads
> Time (mean ± σ): 2.8 ms ± 0.4 ms [User: 1.4 ms, System: 1.2 ms]
> Range (min … max): 1.3 ms … 5.6 ms 957 runs
>
> Summary
> 'git.compile show-ref --heads' ran
> 18.03 ± 3.38 times faster than 'git show-ref --heads'
Excellent speedup.
> - for_each_ref(show_ref, NULL);
> + if (heads_only || tags_only) {
> + if (heads_only)
> + for_each_fullref_in("refs/heads/", show_ref, NULL);
> + if (tags_only)
> + for_each_fullref_in("refs/tags/", show_ref, NULL);
This looks a little silly if these were truly "only" (they
could not both be true), but indeed they could both be true
and the names are just slightly misleading.
Indeed, t1403-show-ref.sh tests all combinations of these
options.
> + } else {
> + for_each_ref(show_ref, NULL);
> + }
Thanks for finding this!
-Stolee
