@matheusbsbs / matheus-bagliano / commits / 1343c89313

revision.c: consult Bloom filters for root commits

The commit-graph stores changed-path Bloom filters which represent the set of paths included in a tree-level diff between a commit's root tree and that of its parent. When a commit has no parents, the tree-diff is computed against that commit's root tree and the empty tree. In other words, every path in that commit's tree is stored in the Bloom filter (since they all appear in the diff). Consult these filters during pathspec-limited traversals in the function `rev_same_tree_as_empty()`. Doing so yields a performance improvement where we can avoid enumerating the full set of paths in a parentless commit's root tree when we know that the path(s) of interest were not listed in that commit's changed-path Bloom filter. Suggested-by: SZEDER Gábor <szeder.dev@gmail.com> Original-patch-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Taylor Blau committed Jun 25, 2024 at 13:39 UTC 1343c893138e63e35b38324387ea790aba77a49f
2 files changed +28 -6
revision.c
+22 -4
@@ -833,17 +833,28 @@ static int rev_compare_tree(struct rev_info *revs,
833 return tree_difference;
834 }
835
836 -static int rev_same_tree_as_empty(struct rev_info *revs, struct commit *commit)
836 +static int rev_same_tree_as_empty(struct rev_info *revs, struct commit *commit,
837 + int nth_parent)
838 {
839 struct tree *t1 = repo_get_commit_tree(the_repository, commit);
840 + int bloom_ret = -1;
841
842 if (!t1)
843 return 0;
844
845 + if (!nth_parent && revs->bloom_keys_nr) {
846 + bloom_ret = check_maybe_different_in_bloom_filter(revs, commit);
847 + if (!bloom_ret)
848 + return 1;
849 + }
850 +
851 tree_difference = REV_TREE_SAME;
852 revs->pruning.flags.has_changes = 0;
853 diff_tree_oid(NULL, &t1->object.oid, "", &revs->pruning);
854
855 + if (bloom_ret == 1 && tree_difference == REV_TREE_SAME)
856 + count_bloom_filter_false_positive++;
857 +
858 return tree_difference == REV_TREE_SAME;
859 }
860
@@ -881,7 +892,7 @@ static int compact_treesame(struct rev_info *revs, struct commit *commit, unsign
892 if (nth_parent != 0)
893 die("compact_treesame %u", nth_parent);
894 old_same = !!(commit->object.flags & TREESAME);
884 - if (rev_same_tree_as_empty(revs, commit))
895 + if (rev_same_tree_as_empty(revs, commit, nth_parent))
896 commit->object.flags |= TREESAME;
897 else
898 commit->object.flags &= ~TREESAME;
@@ -977,7 +988,14 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
988 return;
989
990 if (!commit->parents) {
980 - if (rev_same_tree_as_empty(revs, commit))
991 + /*
992 + * Pretend as if we are comparing ourselves to the
993 + * (non-existent) first parent of this commit object. Even
994 + * though no such parent exists, its changed-path Bloom filter
995 + * (if one exists) is relative to the empty tree, using Bloom
996 + * filters is allowed here.
997 + */
998 + if (rev_same_tree_as_empty(revs, commit, 0))
999 commit->object.flags |= TREESAME;
1000 return;
1001 }
@@ -1058,7 +1076,7 @@ static void try_to_simplify_commit(struct rev_info *revs, struct commit *commit)
1076
1077 case REV_TREE_NEW:
1078 if (revs->remove_empty_trees &&
1061 - rev_same_tree_as_empty(revs, p)) {
1079 + rev_same_tree_as_empty(revs, p, nth_parent)) {
1080 /* We are adding all the specified
1081 * paths from this parent, so the
1082 * history beyond this parent is not
t/t4216-log-bloom.sh
+6 -2
@@ -88,7 +88,11 @@ test_bloom_filters_not_used () {
88 # if the Bloom filter system is initialized, ensure that no
89 # filters were used
90 data="statistics:{"
91 - data="$data\"filter_not_present\":0,"
91 + # unusable filters (e.g., those computed with a
92 + # different value of commitGraph.changedPathsVersion)
93 + # are counted in the filter_not_present bucket, so any
94 + # value is OK there.
95 + data="$data\"filter_not_present\":[0-9][0-9]*,"
96 data="$data\"maybe\":0,"
97 data="$data\"definitely_not\":0,"
98 data="$data\"false_positive\":0}"
@@ -175,7 +179,7 @@ test_expect_success 'setup - add commit-graph to the chain with Bloom filters' '
179
180 test_bloom_filters_used_when_some_filters_are_missing () {
181 log_args=$1
178 - bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"maybe\":6,\"definitely_not\":9"
182 + bloom_trace_prefix="statistics:{\"filter_not_present\":3,\"maybe\":6,\"definitely_not\":10"
183 setup "$log_args" &&
184 grep -q "$bloom_trace_prefix" "$TRASH_DIRECTORY/trace.perf" &&
185 test_cmp log_wo_bloom log_w_bloom