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@xxxxxx>
---
Documentation/rev-list-options.txt | 8 +++++++-
connected.c | 1 +
revision.c | 9 +++++++++
t/t6000-rev-list-misc.sh | 31 ++++++++++++++++++++++++++++++
4 files changed, 48 insertions(+), 1 deletion(-)
diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt
index 24569b06d1..b7bd27e171 100644
--- a/Documentation/rev-list-options.txt
+++ b/Documentation/rev-list-options.txt
@@ -968,6 +968,11 @@ list of the missing objects. Object IDs are prefixed with a ``?'' character.
objects.
endif::git-rev-list[]
+--unsorted-input::
+ Show commits in the order they were given on the command line instead
+ of sorting them in reverse chronological order by commit time. Cannot
+ be combined with `--no-walk` or `--no-walk=sorted`.
+
--no-walk[=(sorted|unsorted)]::
Only show the given commits, but do not traverse their ancestors.
This has no effect if a range is specified. If the argument
@@ -975,7 +980,8 @@ endif::git-rev-list[]
given on the command line. Otherwise (if `sorted` or no argument
was given), the commits are shown in reverse chronological order
by commit time.
- Cannot be combined with `--graph`.
+ Cannot be combined with `--graph`. Cannot be combined with
+ `--unsorted-input` if `sorted` or no argument was given.
--do-walk::
Overrides a previous `--no-walk`.
diff --git a/connected.c b/connected.c
index b18299fdf0..b5f9523a5f 100644
--- a/connected.c
+++ b/connected.c
@@ -106,6 +106,7 @@ int check_connected(oid_iterate_fn fn, void *cb_data,
if (opt->progress)
strvec_pushf(&rev_list.args, "--progress=%s",
_("Checking connectivity"));
+ strvec_push(&rev_list.args, "--unsorted-input");
rev_list.git_cmd = 1;
rev_list.env = opt->env;
diff --git a/revision.c b/revision.c
index 86bbcd10d2..47541407d2 100644
--- a/revision.c
+++ b/revision.c
@@ -2256,6 +2256,10 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
} else if (!strcmp(arg, "--author-date-order")) {
revs->sort_order = REV_SORT_BY_AUTHOR_DATE;
revs->topo_order = 1;
+ } else if (!strcmp(arg, "--unsorted-input")) {
+ if (revs->no_walk)
+ die(_("--unsorted-input is incompatible with --no-walk"));
+ revs->unsorted_input = 1;
} else if (!strcmp(arg, "--early-output")) {
revs->early_output = 100;
revs->topo_order = 1;
@@ -2651,8 +2655,13 @@ static int handle_revision_pseudo_opt(const char *submodule,
} else if (!strcmp(arg, "--not")) {
*flags ^= UNINTERESTING | BOTTOM;
} else if (!strcmp(arg, "--no-walk")) {
+ if (!revs->no_walk && revs->unsorted_input)
+ die(_("--no-walk is incompatible with --unsorted-input"));
revs->no_walk = 1;
} else if (skip_prefix(arg, "--no-walk=", &optarg)) {
+ if (!revs->no_walk && revs->unsorted_input)
+ die(_("--no-walk is incompatible with --unsorted-input"));
+
/*
* Detached form ("--no-walk X" as opposed to "--no-walk=X")
* not allowed, since the argument is optional.
diff --git a/t/t6000-rev-list-misc.sh b/t/t6000-rev-list-misc.sh
index 12def7bcbf..ef849e5bc8 100755
--- a/t/t6000-rev-list-misc.sh
+++ b/t/t6000-rev-list-misc.sh
@@ -169,4 +169,35 @@ test_expect_success 'rev-list --count --objects' '
test_line_count = $count actual
'
+test_expect_success 'rev-list --unsorted-input results in different sorting' '
+ git rev-list --unsorted-input HEAD HEAD~ >first &&
+ git rev-list --unsorted-input HEAD~ HEAD >second &&
+ ! test_cmp first second &&
+ sort first >first.sorted &&
+ sort second >second.sorted &&
+ test_cmp first.sorted second.sorted
+'
+
+test_expect_success 'rev-list --unsorted-input incompatible with --no-walk' '
+ cat >expect <<-EOF &&
+ fatal: --no-walk is incompatible with --unsorted-input
+ EOF
+ test_must_fail git rev-list --unsorted-input --no-walk HEAD 2>error &&
+ test_cmp expect error &&
+ test_must_fail git rev-list --unsorted-input --no-walk=sorted HEAD 2>error &&
+ test_cmp expect error &&
+ test_must_fail git rev-list --unsorted-input --no-walk=unsorted HEAD 2>error &&
+ test_cmp expect error &&
+
+ cat >expect <<-EOF &&
+ fatal: --unsorted-input is incompatible with --no-walk
+ EOF
+ test_must_fail git rev-list --no-walk --unsorted-input HEAD 2>error &&
+ test_cmp expect error &&
+ test_must_fail git rev-list --no-walk=sorted --unsorted-input HEAD 2>error &&
+ test_cmp expect error &&
+ test_must_fail git rev-list --no-walk=unsorted --unsorted-input HEAD 2>error &&
+ test_cmp expect error
+'
+
test_done
--
2.32.0
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