From: Patrick Steinhardt <ps@pks.im>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, "Jeff King" <peff@peff.net>,
"Felipe Contreras" <felipe.contreras@gmail.com>,
"SZEDER Gábor" <szeder.dev@gmail.com>,
"Chris Torek" <chris.torek@gmail.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"Taylor Blau" <me@ttaylorr.com>
Subject: Re: [PATCH v3 4/4] revision: avoid hitting packfiles when commits are in commit-graph
Date: Thu, 5 Aug 2021 13:01:46 +0200 [thread overview]
Message-ID: <YQvFGuf3Ba/5UNXk@ncase> (raw)
In-Reply-To: <xmqqmtpytcny.fsf@gitster.g>
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On Tue, Aug 03, 2021 at 02:56:49PM -0700, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
>
> > I wonder what our stance on this is. I can definitely understand the
> > angle that this would be a deal breaker given that we now claim commits
> > exist which don't anymore.
>
> An optimization that produces a wrong result very fast is a useless
> optimization that has no place in our codebase. But don't we have
> some clue recorded in the commit graph file that tells us with what
> packfile the graph is to be used (iow, if the named packfile still
> exists there, the objects recorded in the graph file are to be found
> there) or something?
Unfortunately, no. For bitmaps we have this information given that a
bitmap is tied to a specific pack anyway. But for commit-graphs, the
story is different given that they don't really care about the packs per
se, but only about the commits.
I was briefly wondering whether we can somehow use generation numbers to
cut off parsing some commits: given we have already observed a commit
with generation number N and we have determined that this commit's
object exists, and we now see a commit with generation number M with
M<N, then we can skip the object lookup because M is reachable by N and
thus its object must exist. But generation numbers cannot determine
reachability, but only unreachability, so I fear this is not possible.
We can do the following on top though:
diff --git a/revision.c b/revision.c
index 3527ef3f65..9e62de20ab 100644
--- a/revision.c
+++ b/revision.c
@@ -368,6 +368,8 @@ static struct object *get_reference(struct rev_info *revs, const char *name,
object = NULL;
goto out;
}
+ } else if (!repo_has_object_file(revs->repo, oid)) {
+ die("bad object %s", name);
}
}
We assert that the object exists, but `repo_has_object_file()` won't try
to unpack the object header given that we request no info about the
object. And because the object ID has been part of the commit-graph, we
know that it's a commit. It's a bit slower compared to the version where
we don't assert object existence, but still a lot faster compared to
looking up the object type via the ODB:
Benchmark #1: HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $(cat newrev)
Time (mean ± σ): 4.512 s ± 0.057 s [User: 4.131 s, System: 0.381 s]
Range (min … max): 4.435 s … 4.632 s 10 runs
Benchmark #2: without-existence rev-list --unsorted-input --objects --quiet --not --all --not $(cat newrev)
Time (mean ± σ): 2.903 s ± 0.022 s [User: 2.533 s, System: 0.369 s]
Range (min … max): 2.878 s … 2.954 s 10 runs
Benchmark #3: with-existence: rev-list --unsorted-input --objects --quiet --not --all --not $(cat newrev)
Time (mean ± σ): 3.071 s ± 0.014 s [User: 2.712 s, System: 0.358 s]
Range (min … max): 3.050 s … 3.088 s 10 runs
Summary
'without-existence: rev-list --unsorted-input --objects --quiet --not --all --not $(cat newrev)' ran
1.06 ± 0.01 times faster than 'with-existance: rev-list --unsorted-input --objects --quiet --not --all --not $(cat newrev)'
1.55 ± 0.02 times faster than 'HEAD~: rev-list --unsorted-input --objects --quiet --not --all --not $(cat newrev)'
Patrick
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next prev parent reply other threads:[~2021-08-05 11:01 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-28 5:33 [PATCH v2 0/3] Speed up connectivity checks via bitmaps Patrick Steinhardt
2021-06-28 5:33 ` [PATCH v2 1/3] p5400: add perf tests for git-receive-pack(1) Patrick Steinhardt
2021-06-28 7:49 ` Ævar Arnfjörð Bjarmason
2021-06-29 6:18 ` Patrick Steinhardt
2021-06-29 12:09 ` Ævar Arnfjörð Bjarmason
2021-06-28 5:33 ` [PATCH v2 2/3] receive-pack: skip connectivity checks on delete-only commands Patrick Steinhardt
2021-06-28 8:00 ` Ævar Arnfjörð Bjarmason
2021-06-28 8:06 ` Ævar Arnfjörð Bjarmason
2021-06-29 6:26 ` Patrick Steinhardt
2021-06-30 1:31 ` Jeff King
2021-06-30 1:35 ` Jeff King
2021-06-30 13:52 ` Patrick Steinhardt
2021-06-28 5:33 ` [PATCH v2 3/3] connected: implement connectivity check using bitmaps Patrick Steinhardt
2021-06-28 20:23 ` Taylor Blau
2021-06-29 22:44 ` Taylor Blau
2021-06-30 2:04 ` Jeff King
2021-06-30 3:07 ` Taylor Blau
2021-06-30 5:45 ` Jeff King
2021-07-02 17:44 ` Taylor Blau
2021-07-02 21:21 ` Jeff King
2021-06-30 1:51 ` Jeff King
2021-07-20 14:26 ` Patrick Steinhardt
2021-08-02 9:37 ` [PATCH v3 0/4] Speed up connectivity checks Patrick Steinhardt
2021-08-02 9:38 ` [PATCH v3 1/4] connected: do not sort input revisions Patrick Steinhardt
2021-08-02 12:49 ` Ævar Arnfjörð Bjarmason
2021-08-03 8:50 ` Patrick Steinhardt
2021-08-04 11:01 ` Ævar Arnfjörð Bjarmason
2021-08-02 19:00 ` Junio C Hamano
2021-08-03 8:55 ` Patrick Steinhardt
2021-08-03 21:47 ` Junio C Hamano
2021-08-02 9:38 ` [PATCH v3 2/4] revision: stop retrieving reference twice Patrick Steinhardt
2021-08-02 12:53 ` Ævar Arnfjörð Bjarmason
2021-08-02 9:38 ` [PATCH v3 3/4] revision: avoid loading object headers multiple times Patrick Steinhardt
2021-08-02 12:55 ` Ævar Arnfjörð Bjarmason
2021-08-05 10:12 ` Patrick Steinhardt
2021-08-02 19:40 ` Junio C Hamano
2021-08-03 9:07 ` Patrick Steinhardt
2021-08-06 14:17 ` Patrick Steinhardt
2021-08-02 9:38 ` [PATCH v3 4/4] revision: avoid hitting packfiles when commits are in commit-graph Patrick Steinhardt
2021-08-02 20:01 ` Junio C Hamano
2021-08-03 9:16 ` Patrick Steinhardt
2021-08-03 21:56 ` Junio C Hamano
2021-08-05 11:01 ` Patrick Steinhardt [this message]
2021-08-05 16:16 ` Junio C Hamano
2021-08-04 10:51 ` Ævar Arnfjörð Bjarmason
2021-08-05 11:25 ` [PATCH v4 0/6] Speed up connectivity checks Patrick Steinhardt
2021-08-05 11:25 ` [PATCH v4 1/6] revision: separate walk and unsorted flags Patrick Steinhardt
2021-08-05 18:47 ` Junio C Hamano
2021-08-05 11:25 ` [PATCH v4 2/6] connected: do not sort input revisions Patrick Steinhardt
2021-08-05 18:44 ` Junio C Hamano
2021-08-06 6:00 ` Patrick Steinhardt
2021-08-06 16:50 ` Junio C Hamano
2021-08-05 11:25 ` [PATCH v4 3/6] revision: stop retrieving reference twice Patrick Steinhardt
2021-08-05 11:25 ` [PATCH v4 4/6] revision: avoid loading object headers multiple times Patrick Steinhardt
2021-08-05 11:25 ` [PATCH v4 5/6] commit-graph: split out function to search commit position Patrick Steinhardt
2021-08-05 11:25 ` [PATCH v4 6/6] revision: avoid hitting packfiles when commits are in commit-graph Patrick Steinhardt
2021-08-09 8:00 ` [PATCH v5 0/5] Speed up connectivity checks Patrick Steinhardt
2021-08-09 8:02 ` Patrick Steinhardt
2021-08-09 8:11 ` Patrick Steinhardt
2021-08-09 8:11 ` [PATCH v5 1/5] revision: separate walk and unsorted flags Patrick Steinhardt
2021-08-09 8:11 ` [PATCH v5 2/5] connected: do not sort input revisions Patrick Steinhardt
2021-08-09 8:11 ` [PATCH v5 3/5] revision: stop retrieving reference twice Patrick Steinhardt
2021-08-09 8:11 ` [PATCH v5 4/5] commit-graph: split out function to search commit position Patrick Steinhardt
2021-08-09 8:12 ` [PATCH v5 5/5] revision: avoid hitting packfiles when commits are in commit-graph Patrick Steinhardt
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