From: Jakub Narebski <jnareb@gmail.com>
To: Stefan Beller <sbeller@google.com>
Cc: "Derrick Stolee" <stolee@gmail.com>, git <git@vger.kernel.org>,
"Jeff King" <peff@peff.net>, "Junio C Hamano" <gitster@pobox.com>,
"Derrick Stolee" <dstolee@microsoft.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: [RFC] Generation Number v2
Date: Sat, 03 Nov 2018 18:27:22 +0100 [thread overview]
Message-ID: <86r2g2ul51.fsf@gmail.com> (raw)
In-Reply-To: 86ftwjzv1h.fsf@gmail.com
Jakub Narebski <jnareb@gmail.com> writes:
> Jakub Narebski <jnareb@gmail.com> writes:
>> Stefan Beller <sbeller@google.com> writes:
> [...]
>>> How would this impact creation of a commit?
>>>
>>> The current generation numbers can be lazily updated or not
>>> updated at all. In my understanding of the maximum generation
>>> numbers, a new commit would make these maximum generation
>>> numbers invalid (i.e. they have to be recomputed).
> [...]
>>> For the V2 maximum generation numbers, would we need to
>>> rewrite the numbers for all commits once we recompute them?
>>> Assuming that is true, it sounds like the benchmark doesn't
>>> cover the whole costs associated with V2, which is why the
>>> exceptional performance can be explained.
>>
>> Let's check it using a simple example
>>
>> First, (minimum) parent-based generation numbers before and after
>> extending the commit graph:
>>
>> 1 2 3 4 5 6 7 new
>> 1 2 3 4 5 - - old
>> .---.-----.---.-----.---*---*
>> \
>> \ 3 4 5 6 new
>> \ 3 4 5 6 old
>> \-.---.-----.---.
>> \
>> \ 5 new
>> \ - old
>> \-*
>
> Let me check yet another idea, using (minimum) parent-based V0 generation
> numbers (counting distance from the sink / root) as a starting number
> for source / heads commits.
[...]
> [...] but let's check another example
>
> 1 2 3 4 5 6 7 8 9 new
> 1 2 3 4 5 6 7 8 - old
> .---.-----.---.---.---.-----.---.---*
> \ /
> \ 3 4 / 5 6 7 8 new
> \ 5 6 / - - - - old
> \-.---.---------/---*---*---*---*
But let's do this correctly.
1 2 3 4 5 6 7 8 9 new
1 2 3 4 5 6 7 8 - old
.---.-----.---.------.---.-----.---.---*
\ /
\ 3 4 / new
\ 5 6 / old
\-.---.------------/
\
\ 5 6 7 8 new
\ - - - - old
\--*---*-----*---*
Well, it looks as if I draw it incorrectly, but performed calculations
right. You may need to modify / change some data, but it looks as if it
is not that much of a problem.
The new version of the maximum generation numbers looks like it gives
the same results as generation numbers for the "longest" path, and
update may affect only the side-branches that were added to. All
branches merged into the trunk, and not added to should be safe with
respect to updating.
Can anyone here prove a thing about update of those modified maximum
generation numbers? Thanks in advance.
Best,
--
Jakub Narębski
next prev parent reply other threads:[~2018-11-03 17:27 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-29 16:55 [RFC] Generation Number v2 Derrick Stolee
2018-10-29 19:22 ` Stefan Beller
2018-10-29 20:06 ` Derrick Stolee
2018-11-01 20:06 ` Jakub Narebski
2018-11-02 9:30 ` Jakub Narebski
2018-11-03 17:27 ` Jakub Narebski [this message]
2018-10-29 20:25 ` Derrick Stolee
2018-11-01 22:13 ` Jakub Narebski
2018-10-30 3:59 ` Junio C Hamano
2018-10-31 12:30 ` Derrick Stolee
2018-11-02 13:33 ` Jakub Narebski
2018-10-31 12:54 ` Ævar Arnfjörð Bjarmason
2018-10-31 13:04 ` Derrick Stolee
2018-11-02 17:44 ` Jakub Narebski
2018-11-01 12:27 ` Jakub Narebski
2018-11-01 13:29 ` Derrick Stolee
2018-11-03 12:33 ` Jakub Narebski
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