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From: Derrick Stolee <stolee@gmail.com>
To: Jeff King <peff@peff.net>, Jonathan Tan <jonathantanmy@google.com>
Cc: gitster@pobox.com, git@vger.kernel.org
Subject: Re: [PATCH on master v2] revision: use commit graph in get_reference()
Date: Thu, 13 Dec 2018 11:20:17 -0500	[thread overview]
Message-ID: <f1d40014-0e05-5fcb-cedc-e07a22c80628@gmail.com> (raw)
In-Reply-To: <20181213012707.GC26210@sigill.intra.peff.net>

On 12/12/2018 8:27 PM, Jeff King wrote:
> On Wed, Dec 12, 2018 at 11:58:12AM -0800, Jonathan Tan wrote:
>
>>> Yeah, this was the part that took me a bit to figure out, as well. The
>>> optimization here is really just avoiding a call to lookup_commit(),
>>> which will do a single hash-table lookup. I wonder if that's actually
>>> worth this more complex interface (as opposed to just always taking an
>>> oid and then always returning a "struct commit", which could be old or
>>> new).
>> Avoidance of lookup_commit() is more important than an optimization, I
>> think. Here, we call lookup_commit() only when we know that that object
>> is a commit (by its presence in a commit graph). If we just called it
>> blindly, we might mistakenly create a commit for that hash when it is
>> actually an object of another type. (We could inline lookup_commit() in
>> parse_commit_in_graph_one(), removing the object creation part, but that
>> adds complexity as well.)
> I was thinking we would only do so in the happy path when we find a
> commit. I.e., something like:
>
>    obj = lookup_object(oid); /* does not auto-vivify */
>    if (obj && obj->parsed)
> 	return obj;
>
>    if (we_have_it_in_commit_graph) {
> 	commit = obj || lookup_commit(oid);
> 	fill_in_details_from_commit_graph(commit);
> 	return &commit->obj;
>    } else {
> 	return parse_object(oid);
>    }
>
> which is more along the lines of that parse_probably_commit() that
> Stolee mentioned.

This approach is what I had in mind. Thanks for making it more concrete!

-Stolee


  reply	other threads:[~2018-12-13 16:20 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-04 22:42 [PATCH on sb/more-repo-in-api] revision: use commit graph in get_reference() Jonathan Tan
2018-12-04 23:12 ` Stefan Beller
2018-12-06 23:36   ` Jonathan Tan
2018-12-07 13:49     ` Derrick Stolee
2018-12-05  4:54 ` Jeff King
2018-12-06 23:54   ` Jonathan Tan
2018-12-07  8:53     ` Jeff King
2018-12-05 23:15 ` Junio C Hamano
2018-12-07 21:50 ` [PATCH on master v2] " Jonathan Tan
2018-12-09  0:51   ` Junio C Hamano
2018-12-09  1:49     ` Junio C Hamano
2018-12-11 10:54     ` Jeff King
2018-12-12 19:58       ` Jonathan Tan
2018-12-13  1:27         ` Jeff King
2018-12-13 16:20           ` Derrick Stolee [this message]
2018-12-13 18:54 ` [PATCH v3] " Jonathan Tan
2018-12-14  3:20   ` Junio C Hamano
2018-12-14  8:45   ` Jeff King
2019-01-25 15:33 ` Regression in: [PATCH on sb/more-repo-in-api] " SZEDER Gábor
2019-01-25 19:56   ` Stefan Beller
2019-01-25 22:01     ` Jonathan Tan
2019-01-25 22:14     ` SZEDER Gábor
2019-01-25 22:21       ` SZEDER Gábor
2019-01-27 13:08         ` [PATCH] object_as_type: initialize commit-graph-related fields of 'struct commit' SZEDER Gábor
2019-01-27 13:28           ` SZEDER Gábor
2019-01-27 18:40             ` Derrick Stolee
2019-01-28 16:15           ` Jeff King
2019-01-28 16:57           ` Jonathan Tan

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