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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: Tue, 25 Jun 2019 06:54:29 -0400	[thread overview]
Message-ID: <55fad895-2c18-5a91-79b9-7b958fe280c6@gmail.com> (raw)
In-Reply-To: <86mui63xwr.fsf@gmail.com>

On 6/25/2019 3:51 AM, Jakub Narebski wrote:
> Jakub Narebski <jnareb@gmail.com> writes:
>> Derrick Stolee <stolee@gmail.com> writes:
>>> On 5/20/2019 7:02 AM, Jakub Narebski wrote:
>>>>
>>>> Are there any blockers that prevent the switch to this
>>>> "generation number v2"?
>>>>
>>>> - Is it a problem with insufficient data to choose the correct numbering
>>>>   as "generation number v2' (there can be only one)?
>>>> - Is it a problem with selected "generation number v2" being
>>>>   incompatibile with gen v2, and Git failing when new version of
>>>>   commit-graph is used instead of softly just not using commit-graph?
>>>> - Or is it something else?
> [...]
> 
>>>                      Using the generation number column for the corrected
>>> commit-date offsets (assuming we also guarantee the offset is strictly
>>> increasing from parent to child), these new values will be backwards-
>>> compatible _except_ for 'git commit-graph verify'.
>>
>> O.K., so the "generation number v2 (legacy)" would be incremental and
>> backward-compatibile in use (though not in generation and validation).
>>
>> Do I understand it correctly how it is calculated:
>>
>>   corrected_date(C) = max(committer_date(C),
>>                           max_{P ∈ parents(C)}(corrected_date(P)) + 1)
>>   offset(C) = corrected_date(C) - committer_date(C)
>>   gen_v2(C) = max(offset(C), max_{P ∈ parents(C)}(gen_v2(P)) + 1) 
> 
> Do you remember who first came up with this idea for backward
> compatibile corrected commit date offsets (monotonically offset
> corrected date)?

I remember saying that the "corrected commit date" that I had suggested
was weak because it was not backwards-compatible with generation numbers
if you are only looking at the offsets. I don't remember who suggested
simply increasing the offset so they do become backwards-compatible.
 
>> Do you have benchmark for this "monotonically offset corrected commit
>> date" generation number in https://github.com/derrickstolee/git/commits/reach-perf
>> and https://github.com/derrickstolee/gen-test ?
> 
> I guess this will have to wait...

I have not had time to revisit this topic and re-run performance
numbers, sorry.

-Stolee

  reply	other threads:[~2019-06-25 10:54 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-18  0:54 Revision walking, commit dates, slop 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
2019-05-23 21:04                       ` Jakub Narebski
2019-06-25  7:51               ` Jakub Narebski
2019-06-25 10:54                 ` Derrick Stolee [this message]
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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