[v4,14/16] builtin/receive-pack.c: avoid enumerating hidden references

Commit Message

Taylor Blau June 20, 2023, 2:22 p.m. UTC

Now that `refs_for_each_fullref_in()` has the ability to avoid
enumerating references matching certain pattern(s), use that to avoid
visiting hidden refs when constructing the ref advertisement via
receive-pack.

Note that since this exclusion is best-effort, we still need
`show_ref_cb()` to check whether or not each reference is hidden or not
before including it in the advertisement.

As was the case when applying this same optimization to `upload-pack`,
`receive-pack`'s reference advertisement phase can proceed much quicker
by avoiding enumerating references that will not be part of the
advertisement.

(Below, we're still using linux.git with one hidden refs/pull/N ref per
commit):

    $ hyperfine -L v ,.compile 'git{v} -c transfer.hideRefs=refs/pull receive-pack --advertise-refs .git'
    Benchmark 1: git -c transfer.hideRefs=refs/pull receive-pack --advertise-refs .git
      Time (mean ± σ):      89.1 ms ±   1.7 ms    [User: 82.0 ms, System: 7.0 ms]
      Range (min … max):    87.7 ms …  95.5 ms    31 runs

    Benchmark 2: git.compile -c transfer.hideRefs=refs/pull receive-pack --advertise-refs .git
      Time (mean ± σ):       4.5 ms ±   0.2 ms    [User: 0.5 ms, System: 3.9 ms]
      Range (min … max):     4.1 ms …   5.6 ms    508 runs

    Summary
      'git.compile -c transfer.hideRefs=refs/pull receive-pack --advertise-refs .git' ran
       20.00 ± 1.05 times faster than 'git -c transfer.hideRefs=refs/pull receive-pack --advertise-refs .git'

Signed-off-by: Taylor Blau <[e-mail]>
---
 builtin/receive-pack.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Patch

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 1a8472eddc..bd5bcc375f 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -337,7 +337,8 @@  static void write_head_info(void)
 {
 	static struct oidset seen = OIDSET_INIT;
 
-	for_each_ref(show_ref_cb, &seen);
+	refs_for_each_fullref_in(get_main_ref_store(the_repository), "",
+				 hidden_refs.v, show_ref_cb, &seen);
 	for_each_alternate_ref(show_one_alternate_ref, &seen);
 	oidset_clear(&seen);
 	if (!sent_capabilities)