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ref-filter: memoize --contains with generations

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git branch and git for-each-ref run a separate reachability walk for
each ref considered by --contains and --no-contains. Refs with shared
history therefore traverse the same commits repeatedly.

git tag instead uses a depth-first walk that caches results across
refs. That walk can perform poorly without generation numbers: a
negative check may walk to the root instead of stopping at a nearby
divergence. Generation numbers let it stop below the oldest target.

Use the memoized walk for all ref-filter callers when generation
numbers are available. Keep git tag on its existing path without
generations. Caching still helps when many tags share deep history:
ffc4b8012d (tag: speed up --contains calculation, 2011-06-11) reduced
git tag --contains HEAD~200 in linux-2.6 from 15.417 to 5.329 seconds.

The new shared-history perf test improves from 0.72 to 0.03 seconds. In
a repository with 62,174 remote-tracking refs, running:

    git branch -r --contains c78ae85f3ce7e

improves from 104.365 seconds to 468 milliseconds.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Tamir Duberstein
2026-06-12 17:49:13 -04:00
committed by Junio C Hamano
parent 5bd39784cd
commit ca96eeee79
2 changed files with 29 additions and 2 deletions
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3
commit-reach.c
View File

@@ -854,7 +854,8 @@ static enum contains_result contains_tag_algo(struct commit *candidate,
int commit_contains(struct ref_filter *filter, struct commit *commit,
struct commit_list *list, struct contains_cache *cache)
{
if (filter->with_commit_tag_algo)
if (filter->with_commit_tag_algo ||
generation_numbers_enabled(the_repository))
return contains_tag_algo(commit, list, cache) == CONTAINS_YES;
return repo_is_descendant_of(the_repository, commit, list);
}

28
t/perf/p1500-graph-walks.sh
View File

@@ -32,7 +32,16 @@ test_expect_success 'setup' '
echo "X:$line" >>test-tool-tags || return 1
done &&
commit=$(git commit-tree $(git rev-parse HEAD^{tree})) &&
git rev-list --first-parent --max-count=8192 HEAD >contains-commits &&
test_file_not_empty contains-commits &&
git update-ref refs/contains-perf-base "$(tail -n 1 contains-commits)" &&
awk "{
printf \"update refs/contains-perf/%04d %s\\n\", NR, \$1
}" contains-commits |
git update-ref --stdin &&
git pack-refs --include "refs/contains-perf/*" &&
commit=$(git commit-tree HEAD^{tree}) &&
git update-ref refs/heads/disjoint-base $commit &&
git commit-graph write --reachable
@@ -62,6 +71,23 @@ test_perf 'contains: git tag --merged' '
xargs git tag --merged=HEAD <tags
'
test_perf 'contains: git for-each-ref' '
git for-each-ref --contains=refs/contains-perf-base --stdin <refs
'
test_perf 'contains: git branch' '
xargs git branch --contains=refs/contains-perf-base <branches
'
test_perf 'contains: git tag' '
xargs git tag --contains=refs/contains-perf-base <tags
'
test_perf 'contains: synthetic shared history' '
git for-each-ref --contains=refs/contains-perf-base \
refs/contains-perf/ >/dev/null
'
test_perf 'is-base check: test-tool reach (refs)' '
test-tool reach get_branch_base_for_tip <test-tool-refs
'