From 3e5e6c6e94f09973d3a72049aad09fd2131a3648 Mon Sep 17 00:00:00 2001 From: Patrick Steinhardt Date: Wed, 4 Aug 2021 15:56:11 +0200 Subject: [PATCH] fetch-pack: speed up loading of refs via commit graph MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When doing reference negotiation, git-fetch-pack(1) is loading all refs from disk in order to determine which commits it has in common with the remote repository. This can be quite expensive in repositories with many references though: in a real-world repository with around 2.2 million refs, fetching a single commit by its ID takes around 44 seconds. Dominating the loading time is decompression and parsing of the objects which are referenced by commits. Given the fact that we only care about commits (or tags which can be peeled to one) in this context, there is thus an easy performance win by switching the parsing logic to make use of the commit graph in case we have one available. Like this, we avoid hitting the object database to parse these commits but instead only load them from the commit-graph. This results in a significant performance boost when executing git-fetch in said repository with 2.2 million refs: Benchmark #1: HEAD~: git fetch $remote $commit Time (mean ± σ): 44.168 s ± 0.341 s [User: 42.985 s, System: 1.106 s] Range (min … max): 43.565 s … 44.577 s 10 runs Benchmark #2: HEAD: git fetch $remote $commit Time (mean ± σ): 19.498 s ± 0.724 s [User: 18.751 s, System: 0.690 s] Range (min … max): 18.629 s … 20.454 s 10 runs Summary 'HEAD: git fetch $remote $commit' ran 2.27 ± 0.09 times faster than 'HEAD~: git fetch $remote $commit' Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano --- fetch-pack.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/fetch-pack.c b/fetch-pack.c index c135635e34..89fdeb3497 100644 --- a/fetch-pack.c +++ b/fetch-pack.c @@ -137,8 +137,14 @@ static struct commit *deref_without_lazy_fetch(const struct object_id *oid, break; } } - if (type == OBJ_COMMIT) - return (struct commit *) parse_object(the_repository, oid); + + if (type == OBJ_COMMIT) { + struct commit *commit = lookup_commit(the_repository, oid); + if (!commit || repo_parse_commit(the_repository, commit)) + return NULL; + return commit; + } + return NULL; }