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From: Derrick Stolee <stolee@gmail.com>
To: Jakub Narebski <jnareb@gmail.com>
Cc: Mike Hommey <mh@glandium.org>,
	SZEDER Gábor <szeder.dev@gmail.com>,
	git@vger.kernel.org
Subject: Re: Revision walking, commit dates, slop
Date: Wed, 22 May 2019 15:06:32 -0400
Message-ID: <f1f2c7f5-9b78-8404-2738-ab895a06c133@gmail.com> (raw)
In-Reply-To: <86lfyyny0p.fsf@gmail.com>

On 5/22/2019 2:29 PM, Jakub Narebski wrote:
> Derrick Stolee <stolee@gmail.com> writes:
>> On 5/20/2019 7:27 PM, Jakub Narebski wrote:
> Restating it yet again:
> 
>    A.  corrected_date(C) = max(committer_date(C),
>                                max_P(committer_date(P) + offset(P)) + 1)
> 
>    B.  offset(C) = max(corrected_date(C) - committer_date(C),
>                        max_P(offset(P)) + 1)

The problem with this definition is that it "defines" the corrected date, and
then _adjusts_ it by updating the offset. I consider

	corrected_date(C) = committer_date(C) + offset(C)

to be part of the definition. You could restate the definition as follows:

	corrected_date = max(committer_date(C) + max_P(offset(P)) + 1,
        	             max_P(corrected_date(P)))

or, equivalently

	corrected_date = max(committer_date(C) + max_P(offset(P)) + 1,
        	             max_P(committer_date(P) + offset(P)))

This definition, in a single step, satisfies the conditions below:

> 
>> The final definition needs two conditions on the offset of a commit C for
>> every parent P:
>>
>>  1. committer_date(C) + offset(C) > committer_date(P) + offset(P)
>>  2. offset(C) > offset(P)

Plus, the "+ 1" in the first step takes into account that "0" is a special offset
value in the commit-graph file format meaning "not computed".

> Well, we should check/test if performance benefits of "offset date"
> ("corrected date with rising offset") truly holds.

Yes, a full performance test will be required. I have full confidence that the
monotonic offset requirement will have only positive effect. That is, it will
not affect the case where committer-date was better than generation number, but will
help the cases where all the committer-dates are equal.

Thanks,
-Stolee


  reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-18  0:54 Mike Hommey
2019-05-18  1:50 ` SZEDER Gábor
2019-05-18  3:58   ` Mike Hommey
2019-05-18  4:17     ` Mike Hommey
2019-05-18 12:01       ` SZEDER Gábor
2019-05-19 22:28         ` Jakub Narebski
2019-05-20  1:33       ` Derrick Stolee
2019-05-20 11:02         ` Jakub Narebski
2019-05-20 11:20           ` Derrick Stolee
2019-05-20 13:42             ` Jakub Narebski
2019-05-20 23:27               ` Jakub Narebski
2019-05-21  1:20                 ` Derrick Stolee
2019-05-22 18:29                   ` Jakub Narebski
2019-05-22 19:06                     ` Derrick Stolee [this message]
2019-05-23 21:04                       ` Jakub Narebski
2019-06-25  7:51               ` Jakub Narebski
2019-06-25 10:54                 ` Derrick Stolee
2019-09-18  8:43                   ` [RFC/PATCH] commit-graph: generation v5 (backward compatible date ceiling) Jakub Narebski
2019-09-18 12:26                     ` Derrick Stolee
2019-05-21 13:14         ` [PATCH] revision: use generation for A..B --topo-order queries Derrick Stolee
2019-05-21 13:59           ` [PATCH 2/2] revision: keep topo-walk free of unintersting commits Derrick Stolee
2019-05-22  2:19             ` Mike Hommey
2019-05-21  2:00   ` Revision walking, commit dates, slop Jonathan Nieder

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