[PATCH v3 1/7] fetch: speed up lookup of want refs via commit-graph
- From
Patrick Steinhardt <ps@pks.im>
- Date
- Sep 1, 2021, 13:09 UTC
- Message-ID
- <8214f04971c4ea628f23d2e9ea143d87570c29d2.1630501732.git.ps@pks.im>
- In-Reply-To
- <cover.1630501732.git.ps@pks.im>
When updating our local refs based on the refs fetched from the remote, we need to iterate through all requested refs and load their respective commits such that we can determine whether they need to be appended to FETCH_HEAD or not. In cases where we're fetching from a remote with exceedingly many refs, resolving these refs can be quite expensive given that we repeatedly need to unpack object headers for each of the referenced objects.
Speed this up by opportunistically trying to resolve object IDs via the commit graph. We only do so for any refs which are not in "refs/tags": more likely than not, these are going to be a commit anyway, and this lets us avoid having to unpack object headers completely in case the object is a commit that is part of the commit-graph. This significantly speeds up mirror-fetches in a real-world repository with 2.3M refs:
Benchmark #1: HEAD~: git-fetch
Time (mean ± σ): 56.482 s ± 0.384 s [User: 53.340 s, System: 5.365 s]
Range (min … max): 56.050 s … 57.045 s 5 runs Benchmark #2: HEAD: git-fetch
Time (mean ± σ): 33.727 s ± 0.170 s [User: 30.252 s, System: 5.194 s]
Range (min … max): 33.452 s … 33.871 s 5 runs Summary
'HEAD: git-fetch' ran
1.67 ± 0.01 times faster than 'HEAD~: git-fetch'Signed-off-by: Patrick Steinhardt <ps@pks.im> --- builtin/fetch.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/builtin/fetch.c b/builtin/fetch.c index 25740c13df..bd7c0da232 100644 --- a/builtin/fetch.c +++ b/builtin/fetch.c @@ -1074,7 +1074,6 @@ static int store_updated_refs(const char *raw_url, const char *remote_name, int connectivity_checked, struct ref *ref_map) { struct fetch_head fetch_head; - struct commit *commit; int url_len, i, rc = 0; struct strbuf note = STRBUF_INIT, err = STRBUF_INIT; struct ref_transaction *transaction = NULL; @@ -1122,6 +1121,7 @@ static int store_updated_refs(const char *raw_url, const char *remote_name, want_status <= FETCH_HEAD_IGNORE; want_status++) { for (rm = ref_map; rm; rm = rm->next) { + struct commit *commit = NULL; struct ref *ref = NULL; if (rm->status == REF_STATUS_REJECT_SHALLOW) { @@ -1131,11 +1131,23 @@ static int store_updated_refs(const char *raw_url, const char *remote_name, continue; } - commit = lookup_commit_reference_gently(the_repository, - &rm->old_oid, - 1); - if (!commit) - rm->fetch_head_status = FETCH_HEAD_NOT_FOR_MERGE; + /* + * References in "refs/tags/" are often going to point + * to annotated tags, which are not part of the + * commit-graph. We thus only try to look up refs in + * the graph which are not in that namespace to not + * regress performance in repositories with many + * annotated tags. + */ + if (!starts_with(rm->name, "refs/tags/")) + commit = lookup_commit_in_graph(the_repository, &rm->old_oid); + if (!commit) { + commit = lookup_commit_reference_gently(the_repository, + &rm->old_oid, + 1); + if (!commit) + rm->fetch_head_status = FETCH_HEAD_NOT_FOR_MERGE; + } if (rm->fetch_head_status != want_status) continue;
-- 2.33.0