@matheusbsbs / matheus-bagliano / commits / f45022dc2f

connected: do not sort input revisions

In order to compute whether objects reachable from a set of tips are all connected, we do a revision walk with these tips as positive references and `--not --all`. `--not --all` will cause the revision walk to load all preexisting references as uninteresting, which can be very expensive in repositories with many references. Benchmarking the git-rev-list(1) command highlights that by far the most expensive single phase is initial sorting of the input revisions: after all references have been loaded, we first sort commits by author date. In a real-world repository with about 2.2 million references, it makes up about 40% of the total runtime of git-rev-list(1). Ultimately, the connectivity check shouldn't really bother about the order of input revisions at all. We only care whether we can actually walk all objects until we hit the cut-off point. So sorting the input is a complete waste of time. Introduce a new "--unsorted-input" flag to git-rev-list(1) which will cause it to not sort the commits and adjust the connectivity check to always pass the flag. This results in the following speedups, executed in a clone of gitlab-org/gitlab [1]: Benchmark #1: git rev-list --objects --quiet --not --all --not $(cat newrev) Time (mean ± σ): 7.639 s ± 0.065 s [User: 7.304 s, System: 0.335 s] Range (min … max): 7.543 s … 7.742 s 10 runs Benchmark #2: git rev-list --unsorted-input --objects --quiet --not --all --not $newrev Time (mean ± σ): 4.995 s ± 0.044 s [User: 4.657 s, System: 0.337 s] Range (min … max): 4.909 s … 5.048 s 10 runs Summary 'git rev-list --unsorted-input --objects --quiet --not --all --not $(cat newrev)' ran 1.53 ± 0.02 times faster than 'git rev-list --objects --quiet --not --all --not $newrev' [1]: https://gitlab.com/gitlab-org/gitlab.git. Note that not all refs are visible to clients. Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Patrick Steinhardt committed Aug 9, 2021 at 10:11 UTC f45022dc2fd692fd024f2eb41a86a66f19013d43
4 files changed +48 -1
Documentation/rev-list-options.txt
+7 -1
@@ -968,6 +968,11 @@ list of the missing objects. Object IDs are prefixed with a ``?'' character.
968 objects.
969 endif::git-rev-list[]
970
971 +--unsorted-input::
972 + Show commits in the order they were given on the command line instead
973 + of sorting them in reverse chronological order by commit time. Cannot
974 + be combined with `--no-walk` or `--no-walk=sorted`.
975 +
976 --no-walk[=(sorted|unsorted)]::
977 Only show the given commits, but do not traverse their ancestors.
978 This has no effect if a range is specified. If the argument
@@ -975,7 +980,8 @@ endif::git-rev-list[]
980 given on the command line. Otherwise (if `sorted` or no argument
981 was given), the commits are shown in reverse chronological order
982 by commit time.
978 - Cannot be combined with `--graph`.
983 + Cannot be combined with `--graph`. Cannot be combined with
984 + `--unsorted-input` if `sorted` or no argument was given.
985
986 --do-walk::
987 Overrides a previous `--no-walk`.
connected.c
+1
@@ -106,6 +106,7 @@ no_promisor_pack_found:
106 if (opt->progress)
107 strvec_pushf(&rev_list.args, "--progress=%s",
108 _("Checking connectivity"));
109 + strvec_push(&rev_list.args, "--unsorted-input");
110
111 rev_list.git_cmd = 1;
112 rev_list.env = opt->env;
revision.c
+9
@@ -2256,6 +2256,10 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
2256 } else if (!strcmp(arg, "--author-date-order")) {
2257 revs->sort_order = REV_SORT_BY_AUTHOR_DATE;
2258 revs->topo_order = 1;
2259 + } else if (!strcmp(arg, "--unsorted-input")) {
2260 + if (revs->no_walk)
2261 + die(_("--unsorted-input is incompatible with --no-walk"));
2262 + revs->unsorted_input = 1;
2263 } else if (!strcmp(arg, "--early-output")) {
2264 revs->early_output = 100;
2265 revs->topo_order = 1;
@@ -2651,8 +2655,13 @@ static int handle_revision_pseudo_opt(const char *submodule,
2655 } else if (!strcmp(arg, "--not")) {
2656 *flags ^= UNINTERESTING | BOTTOM;
2657 } else if (!strcmp(arg, "--no-walk")) {
2658 + if (!revs->no_walk && revs->unsorted_input)
2659 + die(_("--no-walk is incompatible with --unsorted-input"));
2660 revs->no_walk = 1;
2661 } else if (skip_prefix(arg, "--no-walk=", &optarg)) {
2662 + if (!revs->no_walk && revs->unsorted_input)
2663 + die(_("--no-walk is incompatible with --unsorted-input"));
2664 +
2665 /*
2666 * Detached form ("--no-walk X" as opposed to "--no-walk=X")
2667 * not allowed, since the argument is optional.
t/t6000-rev-list-misc.sh
+31
@@ -169,4 +169,35 @@ test_expect_success 'rev-list --count --objects' '
169 test_line_count = $count actual
170 '
171
172 +test_expect_success 'rev-list --unsorted-input results in different sorting' '
173 + git rev-list --unsorted-input HEAD HEAD~ >first &&
174 + git rev-list --unsorted-input HEAD~ HEAD >second &&
175 + ! test_cmp first second &&
176 + sort first >first.sorted &&
177 + sort second >second.sorted &&
178 + test_cmp first.sorted second.sorted
179 +'
180 +
181 +test_expect_success 'rev-list --unsorted-input incompatible with --no-walk' '
182 + cat >expect <<-EOF &&
183 + fatal: --no-walk is incompatible with --unsorted-input
184 + EOF
185 + test_must_fail git rev-list --unsorted-input --no-walk HEAD 2>error &&
186 + test_cmp expect error &&
187 + test_must_fail git rev-list --unsorted-input --no-walk=sorted HEAD 2>error &&
188 + test_cmp expect error &&
189 + test_must_fail git rev-list --unsorted-input --no-walk=unsorted HEAD 2>error &&
190 + test_cmp expect error &&
191 +
192 + cat >expect <<-EOF &&
193 + fatal: --unsorted-input is incompatible with --no-walk
194 + EOF
195 + test_must_fail git rev-list --no-walk --unsorted-input HEAD 2>error &&
196 + test_cmp expect error &&
197 + test_must_fail git rev-list --no-walk=sorted --unsorted-input HEAD 2>error &&
198 + test_cmp expect error &&
199 + test_must_fail git rev-list --no-walk=unsorted --unsorted-input HEAD 2>error &&
200 + test_cmp expect error
201 +'
202 +
203 test_done