@matheusbsbs / matheus-bagliano / commits / 3c1e2c2113

builtin/repack.c: avoid making cruft packs preferred

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>

Taylor Blau committed Oct 3, 2023 at 17:54 UTC 3c1e2c2113842b8462803ef8c9aca596eacfd3af

2 files changed +85 -1

builtin/repack.c

+46 -1

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);

t/t7704-repack-cruft.sh

+39

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