diff mbox series

[v3,1/2] fetch-pack: use commit-graph when computing cutoff

Message ID 077d06764cafde470ea0589072d387d7737bb91e.1644495978.git.ps@pks.im (mailing list archive)
State New, archived
Headers show
Series fetch: speed up mirror-fetches with many refs | expand

Commit Message

Patrick Steinhardt Feb. 10, 2022, 12:28 p.m. UTC
During packfile negotiation we iterate over all refs announced by the
remote side to check whether their IDs refer to commits already known to
us. If a commit is known to us already, then its date is a potential
cutoff point for commits we have in common with the remote side.

There is potentially a lot of commits announced by the remote depending
on how many refs there are in the remote repository, and for every one
of them we need to search for it in our object database and, if found,
parse the corresponding object to find out whether it is a candidate for
the cutoff date. This can be sped up by trying to look up commits via
the commit-graph first, which is a lot more efficient.

Benchmarks in a repository with about 2,1 million refs and an up-to-date
commit-graph show an almost 20% speedup when mirror-fetching:

    Benchmark 1: git fetch +refs/*:refs/* (v2.35.0)
      Time (mean ± σ):     115.587 s ±  2.009 s    [User: 109.874 s, System: 11.305 s]
      Range (min … max):   113.584 s … 118.820 s    5 runs

    Benchmark 2: git fetch +refs/*:refs/* (HEAD)
      Time (mean ± σ):     96.859 s ±  0.624 s    [User: 91.948 s, System: 10.980 s]
      Range (min … max):   96.180 s … 97.875 s    5 runs

    Summary
      'git fetch +refs/*:refs/* (HEAD)' ran
        1.19 ± 0.02 times faster than 'git fetch +refs/*:refs/* (v2.35.0)'

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 fetch-pack.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)
diff mbox series

Patch

diff --git a/fetch-pack.c b/fetch-pack.c
index dd6ec449f2..c5967e228e 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -696,26 +696,30 @@  static void mark_complete_and_common_ref(struct fetch_negotiator *negotiator,
 
 	trace2_region_enter("fetch-pack", "parse_remote_refs_and_find_cutoff", NULL);
 	for (ref = *refs; ref; ref = ref->next) {
-		struct object *o;
+		struct commit *commit;
 
-		if (!has_object_file_with_flags(&ref->old_oid,
+		commit = lookup_commit_in_graph(the_repository, &ref->old_oid);
+		if (!commit) {
+			struct object *o;
+
+			if (!has_object_file_with_flags(&ref->old_oid,
 						OBJECT_INFO_QUICK |
-							OBJECT_INFO_SKIP_FETCH_OBJECT))
-			continue;
-		o = parse_object(the_repository, &ref->old_oid);
-		if (!o)
-			continue;
+						OBJECT_INFO_SKIP_FETCH_OBJECT))
+				continue;
+			o = parse_object(the_repository, &ref->old_oid);
+			if (!o || o->type != OBJ_COMMIT)
+				continue;
+
+			commit = (struct commit *)o;
+		}
 
 		/*
 		 * We already have it -- which may mean that we were
 		 * in sync with the other side at some time after
 		 * that (it is OK if we guess wrong here).
 		 */
-		if (o->type == OBJ_COMMIT) {
-			struct commit *commit = (struct commit *)o;
-			if (!cutoff || cutoff < commit->date)
-				cutoff = commit->date;
-		}
+		if (!cutoff || cutoff < commit->date)
+			cutoff = commit->date;
 	}
 	trace2_region_leave("fetch-pack", "parse_remote_refs_and_find_cutoff", NULL);