pack-objects: support reuse with `--no-ref-delta`
The previous commit disables delta- and bitmap-reuse entirely whenever pack-objects is given '--no-ref-delta' for the sake of simplicity. This is overly pessimistic. When '--delta-base-offset' is also given, delta reuse can remain enabled. A reused delta whose base is written earlier in the output can be encoded as an `OFS_DELTA`, even when its source copy was encoded as a `REF_DELTA`. Preferred bases and external thin-pack bases are different: neither appears in the output, so deltas against either still require encoding the object as a `REF_DELTA`, and thus cannot be reused. Without '--delta-base-offset', delta reuse remains disabled, since no delta representation remains. Bitmap reuse follows a different path, since selected entries may be copied without passing through the code which chooses a delta representation. When given '--no-ref-delta', we must inspect candidate objects individually, and leave `REF_DELTA` entries to the normal object path outside of pack-reuse. We must likewise avoid the special-case for reusing either the single or preferred pack corresponding to the bitmap by whole `eword_t`'s at a time. Signed-off-by: Taylor Blau <ttaylorr@openai.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Taylor Blau committed
Jul 12, 2026 at 18:12 UTC
aca978d38668f74766e14cd75b4461ae356e47bb
5 files changed
+71
-16
builtin/pack-objects.c
+13
-4
index c3574fcb8a..43cd4be2e5 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2207,6 +2207,13 @@ static int can_reuse_delta(const struct object_id *base_oid,
*/
base = packlist_find(&to_pack, base_oid);
if (base) {
+ /*
+ * A preferred base is omitted from the resulting pack, so it
+ * can only be referenced by object ID.
+ */
+ if (base->preferred_base && !allow_ref_delta)
+ return 0;
+
if (!in_same_island(&delta->idx.oid, &base->idx.oid))
return 0;
*base_out = base;
@@ -2218,7 +2225,8 @@ static int can_reuse_delta(const struct object_id *base_oid,
* even if it was buried too deep in history to make it into the
* packing list.
*/
- if (thin && bitmap_has_oid_in_uninteresting(bitmap_git, base_oid)) {
+ if (allow_ref_delta && thin &&
+ bitmap_has_oid_in_uninteresting(bitmap_git, base_oid)) {
if (use_delta_islands) {
if (!in_same_island(&delta->idx.oid, base_oid))
return 0;
@@ -4668,7 +4676,7 @@ static int pack_options_allow_reuse(void)
!ignore_packed_keep_on_disk &&
!ignore_packed_keep_in_core &&
(!local || !have_non_local_packs) &&
- !incremental && allow_ref_delta;
+ !incremental && (allow_ref_delta || allow_ofs_delta);
}
static int get_object_list_from_bitmap(struct rev_info *revs)
@@ -4690,7 +4698,8 @@ static int get_object_list_from_bitmap(struct rev_info *revs)
&reuse_packfiles,
&reuse_packfiles_nr,
&reuse_packfile_bitmap,
- allow_pack_reuse == MULTI_PACK_REUSE);
+ allow_pack_reuse == MULTI_PACK_REUSE,
+ allow_ref_delta);
if (reuse_packfiles) {
reuse_packfile_objects = bitmap_popcount(reuse_packfile_bitmap);
@@ -5317,7 +5326,7 @@ int cmd_pack_objects(int argc,
if (unpack_unreachable || keep_unreachable || pack_loose_unreachable)
use_internal_rev_list = 1;
- if (!reuse_object || !allow_ref_delta)
+ if (!reuse_object || (!allow_ref_delta && !allow_ofs_delta))
reuse_delta = 0;
if (cfg->pack_compression_level == -1)
cfg->pack_compression_level = Z_DEFAULT_COMPRESSION;
pack-bitmap.c
+20
-10
index 83eb47a28b..36cb02e374 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -2267,7 +2267,8 @@ static int try_partial_reuse(struct bitmap_index *bitmap_git,
uint32_t pack_pos,
off_t offset,
struct bitmap *reuse,
- struct pack_window **w_curs)
+ struct pack_window **w_curs,
+ int allow_ref_delta)
{
off_t delta_obj_offset;
enum object_type type;
@@ -2286,6 +2287,9 @@ static int try_partial_reuse(struct bitmap_index *bitmap_git,
uint32_t base_pos;
uint32_t base_bitmap_pos;
+ if (type == OBJ_REF_DELTA && !allow_ref_delta)
+ return 0;
+
/*
* Find the position of the base object so we can look it up
* in our bitmaps. If we can't come up with an offset, or if
@@ -2358,20 +2362,19 @@ static int try_partial_reuse(struct bitmap_index *bitmap_git,
static void reuse_partial_packfile_from_bitmap_1(struct bitmap_index *bitmap_git,
struct bitmapped_pack *pack,
- struct bitmap *reuse)
+ struct bitmap *reuse,
+ int allow_ref_delta)
{
struct bitmap *result = bitmap_git->result;
struct pack_window *w_curs = NULL;
size_t pos = pack->bitmap_pos / BITS_IN_EWORD;
- if (!pack->bitmap_pos) {
+ if (allow_ref_delta && !pack->bitmap_pos) {
/*
* If we're processing the first (in the case of a MIDX, the
* preferred pack) or the only (in the case of single-pack
- * bitmaps) pack, then we can reuse whole words at a time.
- *
- * This is because we know that any deltas in this range *must*
- * have their bases chosen from the same pack, since:
+ * bitmaps) pack, then any delta in this range must have its
+ * base chosen from the same pack:
*
* - In the single pack case, there is no other pack to choose
* them from.
@@ -2380,6 +2383,10 @@ static void reuse_partial_packfile_from_bitmap_1(struct bitmap_index *bitmap_git
* all ties are broken in favor of that pack (i.e. the one
* we're currently processing). So any duplicate bases will be
* resolved in favor of the pack we're processing.
+ *
+ * When REF_DELTAs are allowed, we can therefore reuse whole
+ * words at a time without inspecting object headers. Otherwise,
+ * inspect each object below to avoid reusing a REF_DELTA entry.
*/
while (pos < result->word_alloc &&
pos < pack->bitmap_nr / BITS_IN_EWORD &&
@@ -2429,7 +2436,8 @@ static void reuse_partial_packfile_from_bitmap_1(struct bitmap_index *bitmap_git
}
if (try_partial_reuse(bitmap_git, pack, bit_pos,
- pack_pos, ofs, reuse, &w_curs) < 0) {
+ pack_pos, ofs, reuse, &w_curs,
+ allow_ref_delta) < 0) {
/*
* try_partial_reuse indicated we couldn't reuse
* any bits, so there is no point in trying more
@@ -2464,7 +2472,8 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
struct bitmapped_pack **packs_out,
size_t *packs_nr_out,
struct bitmap **reuse_out,
- int multi_pack_reuse)
+ int multi_pack_reuse,
+ int allow_ref_delta)
{
struct repository *r = bitmap_repo(bitmap_git);
struct bitmapped_pack *packs = NULL;
@@ -2559,7 +2568,8 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
reuse = bitmap_word_alloc(word_alloc);
for (i = 0; i < packs_nr; i++)
- reuse_partial_packfile_from_bitmap_1(bitmap_git, &packs[i], reuse);
+ reuse_partial_packfile_from_bitmap_1(bitmap_git, &packs[i], reuse,
+ allow_ref_delta);
if (bitmap_is_empty(reuse)) {
free(packs);
pack-bitmap.h
+2
-1
index 19a8655457..39b6309736 100644
--- a/pack-bitmap.h
+++ b/pack-bitmap.h
@@ -116,7 +116,8 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
struct bitmapped_pack **packs_out,
size_t *packs_nr_out,
struct bitmap **reuse_out,
- int multi_pack_reuse);
+ int multi_pack_reuse,
+ int allow_ref_delta);
int rebuild_existing_bitmaps(struct bitmap_index *, struct packing_data *mapping,
kh_oid_map_t *reused_bitmaps, int show_progress);
void free_bitmap_index(struct bitmap_index *);
t/t5300-pack-object.sh
+20
-1
index b9e36044b9..02c09e3f7d 100755
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@@ -229,6 +229,20 @@ test_expect_success 'pack without REF_DELTA with OFS_DELTA' '
test_grep ! " REF_DELTA " deltas
'
+test_expect_success 'pack without REF_DELTA reuses deltas as OFS_DELTA' '
+ # Install the REF_DELTA pack above and disable delta search, so any
+ # output delta must be a reused REF_DELTA rewritten as OFS_DELTA.
+ test_when_finished "rm -f .git/objects/pack/pack-$packname_2.*" &&
+ git index-pack --stdin <test-2-${packname_2}.pack >/dev/null &&
+
+ git pack-objects --window=0 --delta-base-offset \
+ --no-ref-delta --stdout <obj-list >reused.pack &&
+ git index-pack -o reused.idx reused.pack &&
+ test-tool pack-deltas --list-deltas reused.idx >deltas &&
+ test_grep " OFS_DELTA " deltas &&
+ test_grep ! " REF_DELTA " deltas
+'
+
test_expect_success 'pack without REF_DELTA skips excluded delta bases' '
test_when_finished "git read-tree $tree" &&
@@ -253,7 +267,12 @@ test_expect_success 'pack without REF_DELTA skips excluded delta bases' '
test_grep ! " OFS_DELTA " deltas &&
test_grep " REF_DELTA " deltas &&
- git pack-objects --thin --stdout --revs \
+ # Store the REF_DELTA entries above and disable delta search below,
+ # so any output delta would have to reuse an excluded-base
+ # REF_DELTA.
+ git index-pack --stdin <thin-fixed.pack >/dev/null &&
+
+ git pack-objects --thin --window=0 --stdout --revs \
--delta-base-offset --no-ref-delta \
<thin-revs >no-ref-thin.pack &&
git index-pack --fix-thin --stdin no-ref-thin-fixed.pack \
t/t5332-multi-pack-reuse.sh
+16
index 881ce668e1..bc479653ec 100755
--- a/t/t5332-multi-pack-reuse.sh
+++ b/t/t5332-multi-pack-reuse.sh
@@ -111,6 +111,22 @@ test_expect_success 'reuse all objects from all packs' '
test_pack_objects_reused_all 9 3
'
+test_expect_success '--no-ref-delta reuses REF_DELTA-free bitmapped packs' '
+ # Whole-word reuse is unavailable under --no-ref-delta, so reusing
+ # every object below exercises the per-object bitmap path.
+ : >trace2.txt &&
+ GIT_TRACE2_EVENT="$PWD/trace2.txt" \
+ git pack-objects --stdout --revs --all --delta-base-offset \
+ --no-ref-delta >got.pack &&
+
+ test_pack_reused 9 <trace2.txt &&
+ test_packs_reused 3 <trace2.txt &&
+
+ git index-pack --strict -o got.idx got.pack &&
+ test-tool pack-deltas --list-deltas got.idx >deltas &&
+ test_grep ! " REF_DELTA " deltas
+'
+
test_expect_success 'reuse objects from first pack with middle gap' '
for i in D E F
do