revision: avoid hitting packfiles when commits are in commit-graph
When queueing references in git-rev-list(1), we try to optimize parsing
of commits via the commit-graph. To do so, we first look up the object's
type, and if it is a commit we call `repo_parse_commit()` instead of
`parse_object()`. This is quite inefficient though given that we're
always uncompressing the object header in order to determine the type.
Instead, we can opportunistically search the commit-graph for the object
ID: in case it's found, we know it's a commit and can directly fill in
the commit object without having to uncompress the object header.
Expose a new function `lookup_commit_in_graph()`, which tries to find a
commit in the commit-graph by ID, and convert `get_reference()` to use
this function. This provides a big performance win in cases where we
load references in a repository with lots of references pointing to
commits. The following has been executed in a real-world repository with
about 2.2 million refs:
Benchmark #1: HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $newrev
Time (mean ± σ): 4.458 s ± 0.044 s [User: 4.115 s, System: 0.342 s]
Range (min … max): 4.409 s … 4.534 s 10 runs
Benchmark #2: HEAD: rev-list --unsorted-input --objects --quiet --not --all --not $newrev
Time (mean ± σ): 3.089 s ± 0.015 s [User: 2.768 s, System: 0.321 s]
Range (min … max): 3.061 s … 3.105 s 10 runs
Summary
'HEAD: rev-list --unsorted-input --objects --quiet --not --all --not $newrev' ran
1.44 ± 0.02 times faster than 'HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $newrev'
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/revision.c b/revision.c
index 80a5989..0dabb5a 100644
--- a/revision.c
+++ b/revision.c
@@ -360,20 +360,18 @@ static struct object *get_reference(struct rev_info *revs, const char *name,
unsigned int flags)
{
struct object *object;
+ struct commit *commit;
/*
- * If the repository has commit graphs, repo_parse_commit() avoids
- * reading the object buffer, so use it whenever possible.
+ * If the repository has commit graphs, we try to opportunistically
+ * look up the object ID in those graphs. Like this, we can avoid
+ * parsing commit data from disk.
*/
- if (oid_object_info(revs->repo, oid, NULL) == OBJ_COMMIT) {
- struct commit *c = lookup_commit(revs->repo, oid);
- if (!repo_parse_commit(revs->repo, c))
- object = (struct object *) c;
- else
- object = NULL;
- } else {
+ commit = lookup_commit_in_graph(revs->repo, oid);
+ if (commit)
+ object = &commit->object;
+ else
object = parse_object(revs->repo, oid);
- }
if (!object) {
if (revs->ignore_missing)
