[PATCH v4 6/6] revision: avoid hitting packfiles when commits are in commit-graph

From

Patrick Steinhardt <ps@pks.im>

Date

Aug 5, 2021, 11:25 UTC

Message-ID

<900c5a9c60282e0fb57840305cbab013ffa398f1.1628162156.git.ps@pks.im>

In-Reply-To

<cover.1628162156.git.ps@pks.im>

    Benchmark #1: HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $newrev
      Time (mean ± σ):      4.508 s ±  0.039 s    [User: 4.131 s, System: 0.377 s]
      Range (min … max):    4.455 s …  4.576 s    10 runs

    Benchmark #2: HEAD: rev-list --unsorted-input --objects --quiet --not --all --not $newrev
      Time (mean ± σ):      3.072 s ±  0.031 s    [User: 2.707 s, System: 0.365 s]
      Range (min … max):    3.040 s …  3.144 s    10 runs

    Summary
      'HEAD: rev-list --unsorted-input --objects --quiet --not --all --not $newrev' ran
        1.47 ± 0.02 times faster than 'HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $newrev'

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 commit-graph.c | 26 ++++++++++++++++++++++++++
 commit-graph.h |  7 +++++++
 revision.c     | 17 +++++++++++++++--
 3 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/commit-graph.c b/commit-graph.c
index 8c4c7262c8..cc7136243d 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -891,6 +891,32 @@ static int find_commit_pos_in_graph(struct commit *item, struct commit_graph *g,
 	}
 }
 
+int parse_commit_in_graph_gently(struct repository *repo, struct object *object)
+{
+	struct commit *commit;
+	uint32_t pos;
+
+	if (object->parsed) {
+		if (object->type != OBJ_COMMIT)
+			return -1;
+		return 0;
+	}
+
+	if (!repo->objects->commit_graph)
+		return -1;
+
+	if (!search_commit_pos_in_graph(&object->oid, repo->objects->commit_graph, &pos))
+		return -1;
+
+	commit = object_as_type(object, OBJ_COMMIT, 1);
+	if (!commit)
+		return -1;
+	if (!fill_commit_in_graph(repo, commit, repo->objects->commit_graph, pos))
+		return -1;
+
+	return 0;
+}
+
 static int parse_commit_in_graph_one(struct repository *r,
 				     struct commit_graph *g,
 				     struct commit *item)
diff --git a/commit-graph.h b/commit-graph.h
index 96c24fb577..e2e93b0ee1 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -40,6 +40,13 @@ int open_commit_graph(const char *graph_file, int *fd, struct stat *st);
  */
 int parse_commit_in_graph(struct repository *r, struct commit *item);
 
+/*
+ * Given an object of unknown type, try to fill in the object in case it is a
+ * commit part of the commit-graph. Returns 0 if the object is a parsed commit
+ * or if it could be filled in via the commit graph, otherwise it returns -1.
+ */
+int parse_commit_in_graph_gently(struct repository *repo, struct object *object);
+
 /*
  * It is possible that we loaded commit contents from the commit buffer,
  * but we also want to ensure the commit-graph content is correctly
diff --git a/revision.c b/revision.c
index 25f4784fdd..318b43026e 100644
--- a/revision.c
+++ b/revision.c
@@ -362,8 +362,21 @@ static struct object *get_reference(struct rev_info *revs, const char *name,
 	struct object *object = lookup_unknown_object(revs->repo, oid);
 
 	if (object->type == OBJ_NONE) {
-		int type = oid_object_info(revs->repo, oid, NULL);
-		if (type < 0 || !object_as_type(object, type, 1)) {
+		/*
+		 * It's likely that the reference points to a commit, so we
+		 * first try to look it up via the commit-graph. If successful,
+		 * then we know it's a commit and don't have to unpack the
+		 * object header. We still need to assert that the object
+		 * exists, but given that we don't request any info about the
+		 * object this is a lot faster than `oid_object_info()`.
+		 */
+		if (parse_commit_in_graph_gently(revs->repo, object) < 0) {
+			int type = oid_object_info(revs->repo, oid, NULL);
+			if (type < 0 || !object_as_type(object, type, 1)) {
+				object = NULL;
+				goto out;
+			}
+		} else if (!repo_has_object_file(revs->repo, oid)) {
 			object = NULL;
 			goto out;
 		}

-- 
2.32.0