From f45022dc2fd692fd024f2eb41a86a66f19013d43 Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Mon, 9 Aug 2021 10:11:50 +0200 Subject: connected: do not sort input revisions MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In order to compute whether objects reachable from a set of tips are all connected, we do a revision walk with these tips as positive references and `--not --all`. `--not --all` will cause the revision walk to load all preexisting references as uninteresting, which can be very expensive in repositories with many references. Benchmarking the git-rev-list(1) command highlights that by far the most expensive single phase is initial sorting of the input revisions: after all references have been loaded, we first sort commits by author date. In a real-world repository with about 2.2 million references, it makes up about 40% of the total runtime of git-rev-list(1). Ultimately, the connectivity check shouldn't really bother about the order of input revisions at all. We only care whether we can actually walk all objects until we hit the cut-off point. So sorting the input is a complete waste of time. Introduce a new "--unsorted-input" flag to git-rev-list(1) which will cause it to not sort the commits and adjust the connectivity check to always pass the flag. This results in the following speedups, executed in a clone of gitlab-org/gitlab [1]: Benchmark #1: git rev-list --objects --quiet --not --all --not $(cat newrev) Time (mean ± σ): 7.639 s ± 0.065 s [User: 7.304 s, System: 0.335 s] Range (min … max): 7.543 s … 7.742 s 10 runs Benchmark #2: git rev-list --unsorted-input --objects --quiet --not --all --not $newrev Time (mean ± σ): 4.995 s ± 0.044 s [User: 4.657 s, System: 0.337 s] Range (min … max): 4.909 s … 5.048 s 10 runs Summary 'git rev-list --unsorted-input --objects --quiet --not --all --not $(cat newrev)' ran 1.53 ± 0.02 times faster than 'git rev-list --objects --quiet --not --all --not $newrev' [1]: https://gitlab.com/gitlab-org/gitlab.git. Note that not all refs are visible to clients. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- connected.c | 1 + 1 file changed, 1 insertion(+) (limited to 'connected.c') diff --git a/connected.c b/connected.c index b18299fdf0..b5f9523a5f 100644 --- a/connected.c +++ b/connected.c @@ -106,6 +106,7 @@ no_promisor_pack_found: if (opt->progress) strvec_pushf(&rev_list.args, "--progress=%s", _("Checking connectivity")); + strvec_push(&rev_list.args, "--unsorted-input"); rev_list.git_cmd = 1; rev_list.env = opt->env; -- cgit v1.3