From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: Taylor Blau <me@ttaylorr.com>,
git@vger.kernel.org, dstolee@microsoft.com
Subject: Re: [PATCH 1/1] commit-graph.c: avoid unnecessary tag dereference when merging
Date: Sat, 21 Mar 2020 11:50:47 -0700 [thread overview]
Message-ID: <xmqqfte1a6ew.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <20200321070333.GB1441446@coredump.intra.peff.net> (Jeff King's message of "Sat, 21 Mar 2020 03:03:33 -0400")
Jeff King <peff@peff.net> writes:
> So we weren't actually reading all of the commits even under the old
> code. We were just going into deref_tag(), seeing that the object is
> already parsed, and then quickly returning when we see that we already
> have an OBJ_COMMIT. I suspect most of your timing differences are mostly
> noise.
Noise that contributes largely to ~7% fluctuation? That sounds big.
> I guess --input=stdin-commits is a good way to simulate that. Try this
> (assuming there's already a split-graph file with all of the commits in
> it):
>
> git rev-parse HEAD >input
> time git commit-graph write --input=stdin-commits --split=merge-all <input
> ...
> A more realistic case would probably be feeding a new small pack to
> --input=stdin-packs.
Makes sense.
> At any rate, I think there is a demonstrable speedup there. But
> moreover, I'm pretty sure this existing code is not doing what it
> expects:
>
> /* only add commits if they still exist in the repo */
> result = lookup_commit_reference_gently(ctx->r, &oid, 1);
>
> That won't look at the object database at all if the commit is already
> marked as parsed. And that parsing might have come from the commit graph
> itself, as our earlier attempts showed. So switching to a real
> has_object_file() call is an important _correctness_ fix, even leaving
> aside the speed improvements.
True. has_object_file() asks the question without even
lookup-replace flag set, so it would try to see if the object is
truly there (modulo the "pretended" ones are declared to exist via
the cached-object mechanism).
Do we need to worry about INFO_QUICK and SKIP_FETCH_OBJECT in this
codepath, by the way?
next prev parent reply other threads:[~2020-03-21 18:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-21 3:44 [PATCH 0/1] commit-graph: avoid unnecessary tag deference when merging Taylor Blau
2020-03-21 3:44 ` [PATCH 1/1] commit-graph.c: avoid unnecessary tag dereference " Taylor Blau
2020-03-21 5:00 ` Jeff King
2020-03-21 6:11 ` Taylor Blau
2020-03-21 6:24 ` Taylor Blau
2020-03-21 7:03 ` Jeff King
2020-03-21 17:27 ` Taylor Blau
2020-03-22 5:36 ` Jeff King
2020-03-22 11:04 ` SZEDER Gábor
2020-03-22 18:45 ` looking up object types quickly, was " Jeff King
2020-03-22 19:18 ` Jeff King
2020-03-23 20:15 ` Taylor Blau
2020-03-22 16:45 ` Taylor Blau
2020-03-24 6:06 ` Jeff King
2020-03-21 18:50 ` Junio C Hamano [this message]
2020-03-22 0:03 ` Derrick Stolee
2020-03-22 0:20 ` Taylor Blau
2020-03-22 0:23 ` Derrick Stolee
2020-03-22 5:49 ` Jeff King
2020-03-22 6:04 ` Jeff King
2020-03-22 15:47 ` Taylor Blau
2020-03-24 6:11 ` Jeff King
2020-03-24 23:08 ` Taylor Blau
2020-03-27 8:42 ` Jeff King
2020-03-27 15:03 ` Taylor Blau
2020-03-22 15:44 ` Taylor Blau
2020-03-24 6:14 ` Jeff King
2020-03-21 5:01 ` Junio C Hamano
2020-03-21 4:56 ` [PATCH 0/1] commit-graph: avoid unnecessary tag deference " Junio C Hamano
2020-03-21 5:04 ` Jeff King
2020-03-21 6:12 ` Taylor Blau
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