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authorLibravatar Jeff King <peff@peff.net>2018-11-20 04:50:53 -0500
committerLibravatar Junio C Hamano <gitster@pobox.com>2018-11-21 13:50:28 +0900
commit3949053617652693b659a933a1393f8be189f26a (patch)
tree274ffd2cd3a6c2514e89d9f7f1020bcc4a377633 /builtin
parentpack-objects: zero-initialize tree_depth/layer arrays (diff)
downloadtgif-3949053617652693b659a933a1393f8be189f26a.tar.xz
pack-objects: fix off-by-one in delta-island tree-depth computation
When delta-islands are in use, we need to record the deepest path at which we find each tree and blob. Our loop to do so counts slashes, so "foo" is depth 0, "foo/bar" is depth 1, and so on. However, this neglects root trees, which are represented by the empty string. Those also have depth 0, but are at a layer above "foo". Thus, "foo" should be 1, "foo/bar" at 2, and so on. We use this depth to topo-sort the trees in resolve_tree_islands(). As a result, we may fail to visit a root tree before the sub-trees it contains, and therefore not correctly pass down the island marks. That in turn could lead to missing some delta opportunities (objects are in the same island, but we didn't realize it) or creating unwanted cross-island deltas (one object is in an island another isn't, but we don't realize). In practice, it seems to have only a small effect. Some experiments on the real-world git/git fork network at GitHub showed an improvement of only 0.14% in the resulting clone size. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'builtin')
-rw-r--r--builtin/pack-objects.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index d5d91eeed5..3d70ab1f42 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2709,9 +2709,11 @@ static void show_object(struct object *obj, const char *name, void *data)
if (use_delta_islands) {
const char *p;
- unsigned depth = 0;
+ unsigned depth;
struct object_entry *ent;
+ /* the empty string is a root tree, which is depth 0 */
+ depth = *name ? 1 : 0;
for (p = strchr(name, '/'); p; p = strchr(p + 1, '/'))
depth++;