[PATCH] packfile: skip decompressing and hashing blobs in add_promisor_object()

From: Aaron Plattner <aplattner@nvidia.com>
Date: Dec 4, 2025, 17:21 UTC
Message-ID: <20251204172132.319360-1-aplattner@nvidia.com>

When is_promisor_object() is called for the first time, it lazily initializes a set of all promisor objects by iterating through all objects in promisor packs. For each object, add_promisor_object() calls parse_object(), which decompresses and hashes the entire object.

For repositories with large pack files, this can take an extremely long time. For example, on a production repository with a 176 GB promisor pack:

 $ time ~/git/git/git-rev-list --objects --all --exclude-promisor-objects --quiet
 ________________________________________________________
 Executed in   76.10 mins    fish           external
    usr time   72.10 mins    1.83 millis   72.10 mins
    sys time    3.56 mins    0.17 millis    3.56 mins

add_promisor_object() needs the full object for trees, commits, and tags. But blobs contain no references to other objects, so the function can just insert their oids into the set and move on.

For objects that weren't already parsed, use odb_read_object_info() to query the object type. If it's a blob, just insert it into the oidset without parsing it. This improves performance for very large pack files significantly:

 $ time ~/git/git/git-rev-list --objects --all --exclude-promisor-objects --quiet
 ________________________________________________________
 Executed in  118.76 secs    fish           external
    usr time   50.88 secs   11.02 millis   50.87 secs
    sys time   36.31 secs    0.08 millis   36.31 secs

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
---
 packfile.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/packfile.c b/packfile.c
index 9cc11b6dc5..563fd14f0e 100644
--- a/packfile.c
+++ b/packfile.c
@@ -2309,6 +2309,17 @@ static int add_promisor_object(const struct object_id *oid,
 	if (obj && obj->parsed) {
 		we_parsed_object = 0;
 	} else {
+		/*
+		 * Blobs don't reference other objects, so skip parsing them
+		 * to save time.
+		 */
+		enum object_type type;
+		type = odb_read_object_info(pack->repo->objects, oid, NULL);
+		if (type == OBJ_BLOB) {
+			oidset_insert(set, oid);
+			return 0;
+		}
+
 		we_parsed_object = 1;
 		obj = parse_object(pack->repo, oid);
 	}

-- 
2.52.0