When given a length that equals the current hash algorithm's hex size,
then `repo_find_unique_abbrev_r()` exits early without trying to find an
abbreviation. This is only sensible because there is nothing to
abbreviate in the first place, so searching through objects to find a
unique prefix would be a waste of compute.
What we don't handle though is the case where the user passes a length
greater than the hash length. This is fine in practice as we still
compute the correct result. But at the very least, this is a waste of
resources as we try to abbreviate a value that cannot be abbreviated,
which causes us to hit the object database.
Start to explicitly handle values larger than hexsz to avoid this
performance penalty, which leads to a measureable speedup. The following
benchmark has been executed in linux.git:
Benchmark 1: git -c core.abbrev=9000 log --abbrev-commit (revision = HEAD~)
Time (mean ± σ): 12.812 s ± 0.040 s [User: 12.225 s, System: 0.554 s]
Range (min … max): 12.723 s … 12.857 s 10 runs
Benchmark 2: git -c core.abbrev=9000 log --abbrev-commit (revision = HEAD)
Time (mean ± σ): 11.095 s ± 0.029 s [User: 10.546 s, System: 0.521 s]
Range (min … max): 11.037 s … 11.122 s 10 runs
Summary
git -c core.abbrev=9000 log --abbrev-commit HEAD (revision = HEAD) ran
1.15 ± 0.00 times faster than git -c core.abbrev=9000 log --abbrev-commit HEAD (revision = HEAD~)
Signed-off-by: Patrick Steinhardt <ps@xxxxxx>
---
object-name.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/object-name.c b/object-name.c
index 523af6f64f..1be2ad1a16 100644
--- a/object-name.c
+++ b/object-name.c
@@ -837,7 +837,7 @@ int repo_find_unique_abbrev_r(struct repository *r, char *hex,
}
oid_to_hex_r(hex, oid);
- if (len == hexsz || !len)
+ if (len >= hexsz || !len)
return hexsz;
mad.repo = r;
--
2.45.2.457.g8d94cfb545.dirty
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