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commit-reach: early exit paint_down_to_common for single merge-base

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Commits not in the commit-graph get GENERATION_NUMBER_INFINITY and
sort to the top of the priority queue.  After those, commits with
finite generation numbers are popped in non-increasing order.
When MERGE_BASE_FIND_ALL is not set the first doubly-painted commit
with a finite generation is therefore a best merge-base: no commit
still in the queue can be a descendant of it.  Skip the expensive
STALE drain in this case.

Add MERGE_BASE_FIND_ALL to the merge_base_flags enum.  Callers that
need every merge-base (repo_get_merge_bases_many, repo_get_merge_bases,
repo_in_merge_bases_many, remove_redundant_no_gen) pass the flag to
preserve existing behavior.  git merge-base (without --all) passes 0,
triggering the early exit.

On a 2.2M-commit merge-heavy monorepo with commit-graph:

  HEAD vs ~500:   5,229ms -> 24ms
  HEAD vs ~1000:  4,214ms -> 39ms
  HEAD vs ~5000:  3,799ms -> 46ms
  HEAD vs ~10000: 3,827ms -> 61ms

Signed-off-by: Kristofer Karlsson <krka@spotify.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Kristofer Karlsson
2026-05-11 12:59:12 +00:00
committed by Junio C Hamano
parent 53f9561055
commit 93e5b1680e
4 changed files with 63 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files
builtin/merge-base.c
+2 -1
View File
@@ -11,11 +11,12 @@
static int show_merge_base(struct commit **rev, size_t rev_nr, int show_all)
{
enum merge_base_flags flags = show_all ? MERGE_BASE_FIND_ALL : 0;
struct commit_list *result = NULL, *r;
if (repo_get_merge_bases_many_dirty(the_repository, rev[0],
rev_nr - 1, rev + 1,
0, &result) < 0) {
flags, &result) < 0) {
commit_list_free(result);
return -1;
}
commit-reach.c
+15 -4
View File
@@ -97,6 +97,14 @@ static int paint_down_to_common(struct repository *r,
if (!(commit->object.flags & RESULT)) {
commit->object.flags |= RESULT;
tail = commit_list_append(commit, tail);
/*
* The queue is generation-ordered; no
* remaining common ancestor can be a
* descendant of this one.
*/
if (!(mb_flags & MERGE_BASE_FIND_ALL) &&
generation < GENERATION_NUMBER_INFINITY)
break;
}
/* Mark parents of a found merge stale */
flags |= STALE;
@@ -247,7 +255,8 @@ static int remove_redundant_no_gen(struct repository *r,
min_generation = curr_generation;
}
if (paint_down_to_common(r, array[i], filled,
work, min_generation, 0, &common)) {
work, min_generation,
MERGE_BASE_FIND_ALL, &common)) {
clear_commit_marks(array[i], all_flags);
clear_commit_marks_many(filled, work, all_flags);
commit_list_free(common);
@@ -477,7 +486,8 @@ int repo_get_merge_bases_many(struct repository *r,
struct commit **twos,
struct commit_list **result)
{
return get_merge_bases_many_0(r, one, n, twos, 1, 0, result);
return get_merge_bases_many_0(r, one, n, twos, 1,
MERGE_BASE_FIND_ALL, result);
}
int repo_get_merge_bases_many_dirty(struct repository *r,
@@ -495,7 +505,8 @@ int repo_get_merge_bases(struct repository *r,
struct commit *two,
struct commit_list **result)
{
return get_merge_bases_many_0(r, one, 1, &two, 1, 0, result);
return get_merge_bases_many_0(r, one, 1, &two, 1,
MERGE_BASE_FIND_ALL, result);
}
/*
@@ -540,7 +551,7 @@ int repo_in_merge_bases_many(struct repository *r, struct commit *commit,
struct commit_list *bases = NULL;
int ret = 0, i;
timestamp_t generation, max_generation = GENERATION_NUMBER_ZERO;
enum merge_base_flags mb_flags = 0;
enum merge_base_flags mb_flags = MERGE_BASE_FIND_ALL;
if (ignore_missing_commits)
mb_flags |= MERGE_BASE_IGNORE_MISSING_COMMITS;
commit-reach.h
+6 -1
View File
@@ -19,9 +19,14 @@ int repo_get_merge_bases_many(struct repository *r,
struct commit_list **result);
enum merge_base_flags {
MERGE_BASE_IGNORE_MISSING_COMMITS = (1 << 0),
MERGE_BASE_FIND_ALL = (1 << 1),
};
/* To be used only when object flags after this call no longer matter */
/*
* To be used only when object flags after this call no longer matter.
* Without MERGE_BASE_FIND_ALL and with generation numbers available,
* returns after finding the first merge-base, skipping the STALE drain.
*/
int repo_get_merge_bases_many_dirty(struct repository *r,
struct commit *one, size_t n,
struct commit **twos,
t/t6600-test-reach.sh
+40
View File
@@ -882,4 +882,44 @@ test_expect_success 'rev-list --maximal-only matches merge-base --independent' '
test_cmp expect.sorted actual.sorted
'
# The following tests verify the early-exit optimisation in
# paint_down_to_common when merge-base is invoked without --all.
# Each test checks all four commit-graph configurations.
merge_base_all_modes () {
test_when_finished rm -rf .git/objects/info/commit-graph &&
git merge-base "$@" >actual &&
test_cmp expect actual &&
cp commit-graph-full .git/objects/info/commit-graph &&
git merge-base "$@" >actual &&
test_cmp expect actual &&
cp commit-graph-half .git/objects/info/commit-graph &&
git merge-base "$@" >actual &&
test_cmp expect actual &&
cp commit-graph-no-gdat .git/objects/info/commit-graph &&
git merge-base "$@" >actual &&
test_cmp expect actual
}
test_expect_success 'merge-base without --all (unique base)' '
git rev-parse commit-5-3 >expect &&
merge_base_all_modes commit-5-7 commit-8-3
'
test_expect_success 'merge-base without --all is one of --all results' '
test_when_finished rm -rf .git/objects/info/commit-graph &&
cp commit-graph-full .git/objects/info/commit-graph &&
git merge-base --all commit-5-7 commit-4-8 commit-6-6 commit-8-3 >all &&
git merge-base commit-5-7 commit-4-8 commit-6-6 commit-8-3 >single &&
test_line_count = 1 single &&
grep -F -f single all &&
cp commit-graph-half .git/objects/info/commit-graph &&
git merge-base --all commit-5-7 commit-4-8 commit-6-6 commit-8-3 >all &&
git merge-base commit-5-7 commit-4-8 commit-6-6 commit-8-3 >single &&
test_line_count = 1 single &&
grep -F -f single all
'
test_done