@matheusbsbs / matheus-bagliano / commits / 16445242ed

fetch-pack: avoid quadratic list insertion in mark_complete

We insert the commit pointed to by each ref one-by-one into the "complete" commit_list using insert_by_date. Because each insertion is O(n), we end up with O(n^2) behavior. This typically doesn't matter, because the number of refs is reasonably small. And even if there are a lot of refs, they often point to a smaller set of objects (in which case the optimization in commit ea5f220 keeps our "n" small). However, in pathological repositories (hundreds of thousands of refs, each pointing to a unique commit), this quadratic behavior can make a difference. Since we do not care about the list order until we have finished building it, we can simply keep it unsorted during the insertion phase, then sort it afterwards. On a repository like the one described above, this dropped the time to do a no-op fetch from 2.0s to 1.7s. On normal repositories, it probably does not matter at all, but it does not hurt to protect ourselves from pathological cases. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Jeff King committed Jul 2, 2013 at 02:16 UTC 16445242edd7e90dc564b657043d2a5efca68cb0

1 file changed +2 -1

fetch-pack.c

+2 -1

@@ -505,7 +505,7 @@ static int mark_complete(const char *refname, const unsigned char *sha1, int fla

505 struct commit *commit = (struct commit *)o;

506 if (!(commit->object.flags & COMPLETE)) {

507 commit->object.flags |= COMPLETE;

508 - commit_list_insert_by_date(commit, &complete);

508 + commit_list_insert(commit, &complete);

509 }

510 }

511 return 0;

@@ -622,6 +622,7 @@ static int everything_local(struct fetch_pack_args *args,

622 if (!args->depth) {

623 for_each_ref(mark_complete, NULL);

624 for_each_alternate_ref(mark_alternate_complete, NULL);

625 + commit_list_sort_by_date(&complete);

626 if (cutoff)

627 mark_recent_complete_commits(args, cutoff);

628 }