When doing a `--geometric` repack, we make sure that the preferred pack
(if writing a MIDX) is the largest pack that we *didn't* repack. That
has the effect of keeping the preferred pack in sync with the pack
containing a majority of the repository's reachable objects.
But if the repository happens to double in size, we'll repack
everything. Here we don't specify any `--preferred-pack`, and instead
let the MIDX code choose.
In the past, that worked fine, since there would only be one pack to
choose from: the one we just wrote. But it's no longer necessarily the
case that there is one pack to choose from. It's possible that the
repository also has a cruft pack, too.
If the cruft pack happens to come earlier in lexical order (and has an
earlier mtime than any non-cruft pack), we'll pick that pack as
preferred. This makes it impossible to reuse chunks of the reachable
pack verbatim from pack-objects, so is sub-optimal.
Luckily, this is a somewhat rare circumstance to be in, since we would
have to repack the entire repository during a `--geometric` repack, and
the cruft pack would have to sort ahead of the pack we just created.
Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
---
A small re-roll of the original patch, removing a few paragraphs from
the proposed log message that are irrelevant and impossible to produce
in today's git.git.
For more details, see <ZRyNHRf+tQwV+T6P@nand.local>.
Range-diff against v1:
1: 19d9aae08e ! 1: 0353939351 builtin/repack.c: avoid making cruft packs preferred
@@ Commit message
have to repack the entire repository during a `--geometric` repack, and
the cruft pack would have to sort ahead of the pack we just created.
- Note that this behavior is usually just a performance regression. But
- it's possible it could be a correctness issue.
-
- Suppose an object was duplicated among the cruft and non-cruft pack. The
- MIDX will pick the one from the pack with the lowest mtime, which will
- always be the cruft one. But if the non-cruft pack happens to sort
- earlier in lexical order, we'll treat that one as preferred, but not all
- duplicates will be resolved in favor of that pack.
-
- So if we happened to have an object which appears in both packs
- (e.g., due to a cruft object being freshened, causing it to appear
- loose, and then repacking it via the `--geometric` repack) it's possible
- the duplicate would be picked from the non-preferred pack.
-
Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
## builtin/repack.c ##
builtin/repack.c | 47 ++++++++++++++++++++++++++++++++++++++++-
t/t7704-repack-cruft.sh | 39 ++++++++++++++++++++++++++++++++++
2 files changed, 85 insertions(+), 1 deletion(-)
diff --git a/builtin/repack.c b/builtin/repack.c
index 04770b15fe..a1a893d952 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -355,6 +355,18 @@ static struct generated_pack_data *populate_pack_exts(const char *name)
return data;
}
+static int has_pack_ext(const struct generated_pack_data *data,
+ const char *ext)
+{
+ int i;
+ for (i = 0; i < ARRAY_SIZE(exts); i++) {
+ if (strcmp(exts[i].name, ext))
+ continue;
+ return !!data->tempfiles[i];
+ }
+ BUG("unknown pack extension: '%s'", ext);
+}
+
static void repack_promisor_objects(const struct pack_objects_args *args,
struct string_list *names)
{
@@ -772,6 +784,7 @@ static void midx_included_packs(struct string_list *include,
static int write_midx_included_packs(struct string_list *include,
struct pack_geometry *geometry,
+ struct string_list *names,
const char *refs_snapshot,
int show_progress, int write_bitmaps)
{
@@ -801,6 +814,38 @@ static int write_midx_included_packs(struct string_list *include,
if (preferred)
strvec_pushf(&cmd.args, "--preferred-pack=%s",
pack_basename(preferred));
+ else if (names->nr) {
+ /* The largest pack was repacked, meaning that either
+ * one or two packs exist depending on whether the
+ * repository has a cruft pack or not.
+ *
+ * Select the non-cruft one as preferred to encourage
+ * pack-reuse among packs containing reachable objects
+ * over unreachable ones.
+ *
+ * (Note we could write multiple packs here if
+ * `--max-pack-size` was given, but any one of them
+ * will suffice, so pick the first one.)
+ */
+ for_each_string_list_item(item, names) {
+ struct generated_pack_data *data = item->util;
+ if (has_pack_ext(data, ".mtimes"))
+ continue;
+
+ strvec_pushf(&cmd.args, "--preferred-pack=pack-%s.pack",
+ item->string);
+ break;
+ }
+ } else {
+ /*
+ * No packs were kept, and no packs were written. The
+ * only thing remaining are .keep packs (unless
+ * --pack-kept-objects was given).
+ *
+ * Set the `--preferred-pack` arbitrarily here.
+ */
+ ;
+ }
if (refs_snapshot)
strvec_pushf(&cmd.args, "--refs-snapshot=%s", refs_snapshot);
@@ -1360,7 +1405,7 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
struct string_list include = STRING_LIST_INIT_NODUP;
midx_included_packs(&include, &existing, &names, &geometry);
- ret = write_midx_included_packs(&include, &geometry,
+ ret = write_midx_included_packs(&include, &geometry, &names,
refs_snapshot ? get_tempfile_path(refs_snapshot) : NULL,
show_progress, write_bitmaps > 0);
diff --git a/t/t7704-repack-cruft.sh b/t/t7704-repack-cruft.sh
index dc86ca8269..be3735dff0 100755
--- a/t/t7704-repack-cruft.sh
+++ b/t/t7704-repack-cruft.sh
@@ -372,4 +372,43 @@ test_expect_success '--max-cruft-size ignores non-local packs' '
)
'
+test_expect_success 'reachable packs are preferred over cruft ones' '
+ repo="cruft-preferred-packs" &&
+ git init "$repo" &&
+ (
+ cd "$repo" &&
+
+ # This test needs to exercise careful control over when a MIDX
+ # is and is not written. Unset the corresponding TEST variable
+ # accordingly.
+ sane_unset GIT_TEST_MULTI_PACK_INDEX &&
+
+ test_commit base &&
+ test_commit --no-tag cruft &&
+
+ non_cruft="$(echo base | git pack-objects --revs $packdir/pack)" &&
+ # Write a cruft pack which both (a) sorts ahead of the non-cruft
+ # pack in lexical order, and (b) has an older mtime to appease
+ # the MIDX preferred pack selection routine.
+ cruft="$(echo pack-$non_cruft.pack | git pack-objects --cruft $packdir/pack-A)" &&
+ test-tool chmtime -1000 $packdir/pack-A-$cruft.pack &&
+
+ test_commit other &&
+ git repack -d &&
+
+ git repack --geometric 2 -d --write-midx --write-bitmap-index &&
+
+ # After repacking, there are two packs left: one reachable one
+ # (which is the result of combining both of the existing two
+ # non-cruft packs), and one cruft pack.
+ find .git/objects/pack -type f -name "*.pack" >packs &&
+ test_line_count = 2 packs &&
+
+ # Make sure that the pack we just wrote is marked as preferred,
+ # not the cruft one.
+ pack="$(test-tool read-midx --preferred-pack $objdir)" &&
+ test_path_is_missing "$packdir/$(basename "$pack" ".idx").mtimes"
+ )
+'
+
test_done
--
2.42.0.341.g9d86323b73.dirty
