[PATCH v3 09/16] refs/packed-backend.c: implement jump lists to avoid excluded pattern(s)
- From
Taylor Blau <me@ttaylorr.com>
- Date
- Jun 7, 2023, 10:41 UTC
- Message-ID
- <8066858bf59386eeec68f0f1e4247eeebb6482f7.1686134440.git.me@ttaylorr.com>
- In-Reply-To
- <cover.1686134440.git.me@ttaylorr.com>
When iterating through the `packed-refs` file in order to answer a query like:
$ git for-each-ref --exclude=refs/__hidden__
it would be useful to avoid walking over all of the entries in `refs/__hidden__/*` when possible, since we know that the ref-filter code is going to throw them away anyways.
In certain circumstances, doing so is possible. The algorithm for doing so is as follows:
- For each excluded pattern, find the first record that matches it,
and the first record that *doesn't* match it (i.e. the location
you'd next want to consider when excluding that pattern). - Sort the set of excluded regions from the previous step in ascending
order of the first location within the `packed-refs` file that
matches. - Clean up the results from the previous step: discard empty regions,
and combine adjacent regions.Then when iterating through the `packed-refs` file, if `iter->pos` is ever contained in one of the regions from the previous steps, advance `iter->pos` past the end of that region, and continue enumeration.
Note that we only perform this optimization when none of the excluded pattern(s) have special meta-characters in them. For a pattern like "refs/foo[ac]", the excluded regions ("refs/fooa", "refs/fooc", and everything underneath them) are not connected. A future implementation that handles this case may split the character class (pretending as if two patterns were excluded: "refs/fooa", and "refs/fooc").
There are a few other gotchas worth considering. First, note that the jump list is sorted, so once we jump past a region, we can avoid considering it (or any regions preceding it) again. The member `jump_pos` is used to track the first next-possible region to jump through.
Second, note that the exclusion list is best-effort, since we do not handle loose references, and because of the meta-character issue above.
In repositories with a large number of hidden references, the speed-up can be significant. Tests here are done with a copy of linux.git with a reference "refs/pull/N" pointing at every commit, as in:
$ git rev-list HEAD | awk '{ print "create refs/pull/" NR " " $0 }' |
git update-ref --stdin
$ git pack-refs --all, it is significantly faster to have `for-each-ref` jump over the excluded references, as opposed to filtering them out after the fact:
$ hyperfine \
'git for-each-ref --format="%(objectname) %(refname)" | grep -vE "^[0-9a-f]{40} refs/pull/"' \
'git.compile for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"'
Benchmark 1: git for-each-ref --format="%(objectname) %(refname)" | grep -vE "^[0-9a-f]{40} refs/pull/"
Time (mean ± σ): 802.7 ms ± 2.1 ms [User: 691.6 ms, System: 147.0 ms]
Range (min … max): 800.0 ms … 807.7 ms 10 runs Benchmark 2: git.compile for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"
Time (mean ± σ): 4.7 ms ± 0.3 ms [User: 0.7 ms, System: 4.0 ms]
Range (min … max): 4.3 ms … 6.7 ms 422 runs Summary
'git.compile for-each-ref --format="%(objectname) %(refname)" --exclude="refs/pull"' ran
172.03 ± 9.60 times faster than 'git for-each-ref --format="%(objectname) %(refname)" | grep -vE "^[0-9a-f]{40} refs/pull/"'Using the jump list is fairly straightforward (see the changes to `refs/packed-backend.c::next_record()`), but constructing the list is not. To ensure that the construction is correct, add a new suite of tests in t1419 covering various corner cases (overlapping regions, partially overlapping regions, adjacent regions, etc.).
Co-authored-by: Jeff King <peff@peff.net> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Taylor Blau <me@ttaylorr.com> --- ref-filter.c | 5 +- refs/packed-backend.c | 166 ++++++++++++++++++++++++++++++++++++-- t/helper/test-ref-store.c | 10 +++ t/t1419-exclude-refs.sh | 101 +++++++++++++++++++++++ 4 files changed, 274 insertions(+), 8 deletions(-) create mode 100755 t/t1419-exclude-refs.sh
diff --git a/ref-filter.c b/ref-filter.c index 717c3c4bcf..ddc7f5204f 100644 --- a/ref-filter.c +++ b/ref-filter.c @@ -2210,12 +2210,13 @@ static int for_each_fullref_in_pattern(struct ref_filter *filter, if (!filter->name_patterns[0]) { /* no patterns; we have to look at everything */ return refs_for_each_fullref_in(get_main_ref_store(the_repository), - "", NULL, cb, cb_data); + "", filter->exclude.v, cb, cb_data); } return refs_for_each_fullref_in_prefixes(get_main_ref_store(the_repository), NULL, filter->name_patterns, - NULL, cb, cb_data); + filter->exclude.v, + cb, cb_data); } /* diff --git a/refs/packed-backend.c b/refs/packed-backend.c index 33639f73e1..67327e579c 100644 --- a/refs/packed-backend.c +++ b/refs/packed-backend.c @@ -303,7 +303,8 @@ static int cmp_packed_ref_records(const void *v1, const void *v2) * Compare a snapshot record at `rec` to the specified NUL-terminated * refname. */ -static int cmp_record_to_refname(const char *rec, const char *refname) +static int cmp_record_to_refname(const char *rec, const char *refname, + int start) { const char *r1 = rec + the_hash_algo->hexsz + 1; const char *r2 = refname; @@ -312,7 +313,7 @@ static int cmp_record_to_refname(const char *rec, const char *refname) if (*r1 == '\n') return *r2 ? -1 : 0; if (!*r2) - return 1; + return start ? 1 : -1; if (*r1 != *r2) return (unsigned char)*r1 < (unsigned char)*r2 ? -1 : +1; r1++; @@ -528,7 +529,8 @@ static int load_contents(struct snapshot *snapshot) } static const char *find_reference_location_1(struct snapshot *snapshot, - const char *refname, int mustexist) + const char *refname, int mustexist, + int start) { /* * This is not *quite* a garden-variety binary search, because @@ -558,7 +560,7 @@ static const char *find_reference_location_1(struct snapshot *snapshot, mid = lo + (hi - lo) / 2; rec = find_start_of_record(lo, mid); - cmp = cmp_record_to_refname(rec, refname); + cmp = cmp_record_to_refname(rec, refname, start); if (cmp < 0) { lo = find_end_of_record(mid, hi); } else if (cmp > 0) { @@ -591,7 +593,22 @@ static const char *find_reference_location_1(struct snapshot *snapshot, static const char *find_reference_location(struct snapshot *snapshot, const char *refname, int mustexist) { - return find_reference_location_1(snapshot, refname, mustexist); + return find_reference_location_1(snapshot, refname, mustexist, 1); +} + +/* + * Find the place in `snapshot->buf` after the end of the record for + * `refname`. In other words, find the location of first thing *after* + * `refname`. + * + * Other semantics are identical to the ones in + * `find_reference_location()`. + */ +static const char *find_reference_location_end(struct snapshot *snapshot, + const char *refname, + int mustexist) +{ + return find_reference_location_1(snapshot, refname, mustexist, 0); } /* @@ -785,6 +802,13 @@ struct packed_ref_iterator { /* The end of the part of the buffer that will be iterated over: */ const char *eof; + struct jump_list_entry { + const char *start; + const char *end; + } *jump; + size_t jump_nr, jump_alloc; + size_t jump_pos; + /* Scratch space for current values: */ struct object_id oid, peeled; struct strbuf refname_buf; @@ -802,14 +826,34 @@ struct packed_ref_iterator { */ static int next_record(struct packed_ref_iterator *iter) { - const char *p = iter->pos, *eol; + const char *p, *eol; strbuf_reset(&iter->refname_buf); + /* + * If iter->pos is contained within a skipped region, jump past + * it. + * + * Note that each skipped region is considered at most once, + * since they are ordered based on their starting position. + */ + while (iter->jump_pos < iter->jump_nr) { + struct jump_list_entry *curr = &iter->jump[iter->jump_pos]; + if (iter->pos < curr->start) + break; /* not to the next jump yet */ + + iter->jump_pos++; + if (iter->pos < curr->end) { + iter->pos = curr->end; + break; + } + } + if (iter->pos == iter->eof) return ITER_DONE; iter->base.flags = REF_ISPACKED; + p = iter->pos; if (iter->eof - p < the_hash_algo->hexsz + 2 || parse_oid_hex(p, &iter->oid, &p) || @@ -917,6 +961,7 @@ static int packed_ref_iterator_abort(struct ref_iterator *ref_iterator) int ok = ITER_DONE; strbuf_release(&iter->refname_buf); + free(iter->jump); release_snapshot(iter->snapshot); base_ref_iterator_free(ref_iterator); return ok; @@ -928,6 +973,112 @@ static struct ref_iterator_vtable packed_ref_iterator_vtable = { .abort = packed_ref_iterator_abort }; +static int jump_list_entry_cmp(const void *va, const void *vb) +{ + const struct jump_list_entry *a = va; + const struct jump_list_entry *b = vb; + + if (a->start < b->start) + return -1; + if (a->start > b->start) + return 1; + return 0; +} + +static int has_glob_special(const char *str) +{ + const char *p; + for (p = str; *p; p++) { + if (is_glob_special(*p)) + return 1; + } + return 0; +} + +static const char *ptr_max(const char *x, const char *y) +{ + if (x > y) + return x; + return y; +} + +static void populate_excluded_jump_list(struct packed_ref_iterator *iter, + struct snapshot *snapshot, + const char **excluded_patterns) +{ + size_t i, j; + const char **pattern; + struct jump_list_entry *last_disjoint; + + if (!excluded_patterns) + return; + + for (pattern = excluded_patterns; *pattern; pattern++) { + struct jump_list_entry *e; + + /* + * We can't feed any excludes with globs in them to the + * refs machinery. It only understands prefix matching. + * We likewise can't even feed the string leading up to + * the first meta-character, as something like "foo[a]" + * should not exclude "foobar" (but the prefix "foo" + * would match that and mark it for exclusion). + */ + if (has_glob_special(*pattern)) + continue; + + ALLOC_GROW(iter->jump, iter->jump_nr + 1, iter->jump_alloc); + + e = &iter->jump[iter->jump_nr++]; + e->start = find_reference_location(snapshot, *pattern, 0); + e->end = find_reference_location_end(snapshot, *pattern, 0); + } + + if (!iter->jump_nr) { + /* + * Every entry in exclude_patterns has a meta-character, + * nothing to do here. + */ + return; + } + + QSORT(iter->jump, iter->jump_nr, jump_list_entry_cmp); + + /* + * As an optimization, merge adjacent entries in the jump list + * to jump forwards as far as possible when entering a skipped + * region. + * + * For example, if we have two skipped regions: + * + * [[A, B], [B, C]] + * + * we want to combine that into a single entry jumping from A to + * C. + */ + last_disjoint = iter->jump; + + for (i = 1, j = 1; i < iter->jump_nr; i++) { + struct jump_list_entry *ours = &iter->jump[i]; + + if (ours->start == ours->end) { + /* ignore empty regions (no matching entries) */ + continue; + } else if (ours->start <= last_disjoint->end) { + /* overlapping regions extend the previous one */ + last_disjoint->end = ptr_max(last_disjoint->end, ours->end); + } else { + /* otherwise, insert a new region */ + iter->jump[j++] = *ours; + last_disjoint = ours; + + } + } + + iter->jump_nr = j; + iter->jump_pos = 0; +} + static struct ref_iterator *packed_ref_iterator_begin( struct ref_store *ref_store, const char *prefix, const char **exclude_patterns, @@ -963,6 +1114,9 @@ static struct ref_iterator *packed_ref_iterator_begin( ref_iterator = &iter->base; base_ref_iterator_init(ref_iterator, &packed_ref_iterator_vtable, 1); + if (exclude_patterns) + populate_excluded_jump_list(iter, snapshot, exclude_patterns); + iter->snapshot = snapshot; acquire_snapshot(snapshot); diff --git a/t/helper/test-ref-store.c b/t/helper/test-ref-store.c index 6d8f844e9c..2bff003f7c 100644 --- a/t/helper/test-ref-store.c +++ b/t/helper/test-ref-store.c @@ -175,6 +175,15 @@ static int cmd_for_each_ref(struct ref_store *refs, const char **argv) return refs_for_each_ref_in(refs, prefix, each_ref, NULL); } +static int cmd_for_each_ref__exclude(struct ref_store *refs, const char **argv) +{ + const char *prefix = notnull(*argv++, "prefix"); + const char **exclude_patterns = argv; + + return refs_for_each_fullref_in(refs, prefix, exclude_patterns, each_ref, + NULL); +} + static int cmd_resolve_ref(struct ref_store *refs, const char **argv) { struct object_id oid = *null_oid(); @@ -307,6 +316,7 @@ static struct command commands[] = { { "delete-refs", cmd_delete_refs }, { "rename-ref", cmd_rename_ref }, { "for-each-ref", cmd_for_each_ref }, + { "for-each-ref--exclude", cmd_for_each_ref__exclude }, { "resolve-ref", cmd_resolve_ref }, { "verify-ref", cmd_verify_ref }, { "for-each-reflog", cmd_for_each_reflog }, diff --git a/t/t1419-exclude-refs.sh b/t/t1419-exclude-refs.sh new file mode 100755 index 0000000000..bc534c8ea1 --- /dev/null +++ b/t/t1419-exclude-refs.sh @@ -0,0 +1,101 @@ +#!/bin/sh + +test_description='test exclude_patterns functionality in main ref store' + +GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main +export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME + +TEST_PASSES_SANITIZE_LEAK=true +. ./test-lib.sh + +for_each_ref__exclude () { + test-tool ref-store main for-each-ref--exclude "$@" >actual.raw + cut -d ' ' -f 2 actual.raw +} + +for_each_ref () { + git for-each-ref --format='%(refname)' "$@" +} + +test_expect_success 'setup' ' + test_commit --no-tag base && + base="$(git rev-parse HEAD)" && + + for name in foo bar baz quux + do + for i in 1 2 3 + do + echo "create refs/heads/$name/$i $base" || return 1 + done || return 1 + done >in && + echo "delete refs/heads/main" >>in && + + git update-ref --stdin <in && + git pack-refs --all +' + +test_expect_success 'excluded region in middle' ' + for_each_ref__exclude refs/heads refs/heads/foo >actual && + for_each_ref refs/heads/bar refs/heads/baz refs/heads/quux >expect && + + test_cmp expect actual +' + +test_expect_success 'excluded region at beginning' ' + for_each_ref__exclude refs/heads refs/heads/bar >actual && + for_each_ref refs/heads/baz refs/heads/foo refs/heads/quux >expect && + + test_cmp expect actual +' + +test_expect_success 'excluded region at end' ' + for_each_ref__exclude refs/heads refs/heads/quux >actual && + for_each_ref refs/heads/foo refs/heads/bar refs/heads/baz >expect && + + test_cmp expect actual +' + +test_expect_success 'disjoint excluded regions' ' + for_each_ref__exclude refs/heads refs/heads/bar refs/heads/quux >actual && + for_each_ref refs/heads/baz refs/heads/foo >expect && + + test_cmp expect actual +' + +test_expect_success 'adjacent, non-overlapping excluded regions' ' + for_each_ref__exclude refs/heads refs/heads/bar refs/heads/baz >actual && + for_each_ref refs/heads/foo refs/heads/quux >expect && + + test_cmp expect actual +' + +test_expect_success 'overlapping excluded regions' ' + for_each_ref__exclude refs/heads refs/heads/ba refs/heads/baz >actual && + for_each_ref refs/heads/foo refs/heads/quux >expect && + + test_cmp expect actual +' + +test_expect_success 'several overlapping excluded regions' ' + for_each_ref__exclude refs/heads \ + refs/heads/bar refs/heads/baz refs/heads/foo >actual && + for_each_ref refs/heads/quux >expect && + + test_cmp expect actual +' + +test_expect_success 'non-matching excluded section' ' + for_each_ref__exclude refs/heads refs/heads/does/not/exist >actual && + for_each_ref >expect && + + test_cmp expect actual +' + +test_expect_success 'meta-characters are discarded' ' + for_each_ref__exclude refs/heads "refs/heads/ba*" >actual && + for_each_ref >expect && + + test_cmp expect actual +' + +test_done
-- 2.41.0.16.g26cd413590