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builtin/repack.c: avoid making cruft packs preferred

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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@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Taylor Blau
2023-10-03 17:54:19 -04:00
committed by Junio C Hamano
parent 37dc6d8104
commit 3c1e2c2113
2 changed files with 85 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

47
builtin/repack.c
View File

@ -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);

39
t/t7704-repack-cruft.sh
View File

@ -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