From: Tamir Duberstein Date: Tue, 09 Jun 2026 02:34:57 GMT Subject: [PATCH v2] ref-filter: restore prefix-scoped iteration Message-ID: <20260608-fix-git-branch-regression-v2-1-fd82075a8520@gmail.com> Commit dabecb9db2 (for-each-ref: introduce a '--start-after' option, 2025-07-15) changed single-kind branch, remote-tracking branch, and tag enumeration in do_filter_refs() from constructing an iterator with the namespace prefix to constructing an unscoped iterator and applying the prefix with ref_iterator_seek(). Before that change, refs_for_each_fullref_in() passed the namespace prefix during iterator construction. That helper has since been replaced by refs_for_each_ref_ext(). The files backend primes its loose-ref cache for the construction prefix before it opens packed refs. An empty construction prefix therefore reads every loose ref, and a later seek cannot undo that I/O. Consequently, git branch, git branch --remotes, and git tag scale with unrelated loose refs. Patrick Steinhardt observed during review that iterator construction and seeking accepted similar strings but assigned them different state semantics. Junio C Hamano then pointed out that no current command can combine start_after with this single-kind path, but future branch or tag support would need to keep the namespace while moving the cursor. Keep the existing start_after path unchanged. The iterator API cannot currently seek to one string while retaining another as its prefix: an unflagged seek clears the prefix, while REF_ITERATOR_SEEK_SET_PREFIX replaces it with the seek string. For the commands affected by this regression, which do not set start_after, pass the namespace prefix during iterator construction so that loose refs are scoped before the packed-refs snapshot is opened. This fixes the current regression without deleting the ref-filter state discussed during review or changing its dormant behavior. Add REFFILES-gated performance cases with one branch, one remote-tracking branch, one tag, and 10,000 unrelated loose refs. The benchmarks were run with: GIT_PERF_REPEAT_COUNT=5 GIT_PERF_MAKE_OPTS=-j8 \ t/perf/run a89346e34a . -- p6300-for-each-ref.sh The following are the best of five runs, with each run invoking the command ten times. Times are elapsed seconds with user and system CPU seconds in parentheses: a89346e34a this commit branch 2.74(0.13+2.56) 0.11(0.04+0.04) branch --remotes 2.81(0.13+2.62) 0.12(0.04+0.04) tag 3.01(0.14+2.82) 0.11(0.04+0.04) Both revisions used the default -O2 build flags and a config.mak containing only "NO_REGEX = NeedsStartEnd". They were built with Apple clang 21.0.0 on macOS 26.5. The machine was a MacBook Pro (Mac16,6) with a 16-core Apple M4 Max (12 performance and four efficiency cores) and 128 GB RAM. Link: https://lore.kernel.org/git/aGZidwwlToWThkn8@pks.im/ Link: https://lore.kernel.org/git/xmqqikjq7s16.fsf@gitster.g/ Fixes: dabecb9db2b2 ("for-each-ref: introduce a '--start-after' option") Assisted-by: Codex gpt-5.5 Signed-off-by: Tamir Duberstein --- The series is based on a89346e34a (maint) because the regression has been present in released versions since Git 2.51.0. --- Changes in v2: - Extract local variable `store`. - Link to v1: https://patch.msgid.link/20260605-fix-git-branch-regression-v1-1-02f40ad40929@gmail.com --- ref-filter.c | 28 +++++++++++++++++++--------- t/perf/p6300-for-each-ref.sh | 39 ++++++++++++++++++++++++++++++++++++++- 2 files changed, 57 insertions(+), 10 deletions(-) diff --git a/ref-filter.c b/ref-filter.c index 1da4c0e60d..5cbc007d64 100644 --- a/ref-filter.c +++ b/ref-filter.c @@ -3315,19 +3315,29 @@ static int do_filter_refs(struct ref_filter *filter, unsigned int type, refs_for prefix = "refs/tags/"; if (prefix) { - struct ref_iterator *iter; + struct ref_store *store = get_main_ref_store(the_repository); - iter = refs_ref_iterator_begin(get_main_ref_store(the_repository), - "", NULL, 0, 0); + if (filter->start_after) { + struct ref_iterator *iter; + + iter = refs_ref_iterator_begin(store, "", NULL, 0, 0); - if (filter->start_after) ret = start_ref_iterator_after(iter, filter->start_after); - else - ret = ref_iterator_seek(iter, prefix, - REF_ITERATOR_SEEK_SET_PREFIX); + if (!ret) + ret = do_for_each_ref_iterator(iter, fn, + cb_data); + } else { + /* + * Pass the prefix during construction because the files + * backend primes loose refs before a later seek can + * narrow the iterator. + */ + struct refs_for_each_ref_options opts = { + .prefix = prefix, + }; - if (!ret) - ret = do_for_each_ref_iterator(iter, fn, cb_data); + ret = refs_for_each_ref_ext(store, fn, cb_data, &opts); + } } else if (filter->kind & FILTER_REFS_REGULAR) { ret = for_each_fullref_in_pattern(filter, fn, cb_data); } diff --git a/t/perf/p6300-for-each-ref.sh b/t/perf/p6300-for-each-ref.sh index fa7289c752..ed9c1c6a19 100755 --- a/t/perf/p6300-for-each-ref.sh +++ b/t/perf/p6300-for-each-ref.sh @@ -1,6 +1,6 @@ #!/bin/sh -test_description='performance of for-each-ref' +test_description='performance of ref-filter users' . ./perf-lib.sh test_perf_fresh_repo @@ -84,4 +84,41 @@ test_expect_success 'pack refs' ' ' run_tests "packed" +test_expect_success REFFILES 'setup many unrelated loose refs' ' + git init scoped && + test_commit -C scoped --no-tag base && + test_seq $ref_count_per_type | + sed "s,.*,update refs/custom/unrelated_& HEAD," | + git -C scoped update-ref --stdin && + git -C scoped update-ref refs/remotes/origin/main HEAD && + git -C scoped update-ref refs/tags/only HEAD +' + +test_perf "branch (many unrelated loose refs)" --prereq REFFILES " + ( + cd scoped && + for i in \$(test_seq $test_iteration_count); do + git branch --format='%(refname)' >/dev/null + done + ) +" + +test_perf "branch --remotes (many unrelated loose refs)" --prereq REFFILES " + ( + cd scoped && + for i in \$(test_seq $test_iteration_count); do + git branch --remotes --format='%(refname)' >/dev/null + done + ) +" + +test_perf "tag (many unrelated loose refs)" --prereq REFFILES " + ( + cd scoped && + for i in \$(test_seq $test_iteration_count); do + git tag --format='%(refname)' >/dev/null + done + ) +" + test_done --- base-commit: a89346e34a937f001e5d397ee62224e3e9852040 change-id: 20260605-fix-git-branch-regression-9e4236f18091 Best regards, -- Tamir Duberstein