From: Jakub Narebski <jnareb@gmail.com>
To: Derrick Stolee <stolee@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 20:29:26 +0200 [thread overview]
Message-ID: <86lfyyny0p.fsf@gmail.com> (raw)
In-Reply-To: <88662e18-db51-cb48-3307-0ea2a91c4ebe@gmail.com> (Derrick Stolee's message of "Mon, 20 May 2019 21:20:45 -0400")
Derrick Stolee <stolee@gmail.com> writes:
> On 5/20/2019 7:27 PM, 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"?
>> [...]
>>
>>>> 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)
>>
>> This should probably read
>>
>> offset_date(P) = committer_date(P) + gen_v2(P)
>> corrected_date(C) = max(committer_date(C),
>> max_{P ∈ parents(C)}(offset_date(P)) + 1)
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 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)
The equation (B) ensures the (2) condition, i.e offset(C) > offset(P).
The equation (A) ensures that condition (1) is fulfulled, because from
(B) we have
corrected_date(C) <= committer_date(C) + offset(C)
This from (B) and (A( we get:
committer_date(C) + offset(C) >= corrected_date(C) >
> committer_date(P) + offset(P)
> Condition (1) will give us the performance benefits related to the
> committer-date heuristic. Condition (2) will give us backwards-compatibility
> with generation numbers.
Well, we should check/test if performance benefits of "offset date"
("corrected date with rising offset") truly holds.
Best,
--
Jakub Narębski
next prev parent reply other threads:[~2019-05-22 18:29 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 [this message]
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
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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