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From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Derrick Stolee <stolee@gmail.com>, Git List <git@vger.kernel.org>,
	Jeff King <peff@peff.net>, Jakub Narębski <jnareb@gmail.com>,
	Derrick Stolee <dstolee@microsoft.com>
Subject: Re: [RFC] Generation Number v2
Date: Wed, 31 Oct 2018 13:54:48 +0100
Message-ID: <875zxil1if.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <xmqqy3ag13us.fsf@gitster-ct.c.googlers.com>


On Tue, Oct 30 2018, Junio C Hamano wrote:

> Derrick Stolee <stolee@gmail.com> writes:
>> In contrast, maximum generation numbers and corrected commit
>> dates both performed quite well. They are frequently the top
>> two performing indexes, and rarely significantly different.
>>
>> The trade-off here now seems to be: which _property_ is more important,
>> locally-computable or backwards-compatible?
>
> Nice summary.
>
> As I already said, I personally do not think being compatible with
> currently deployed clients is important at all (primarily because I
> still consider the whole thing experimental), and there is a clear
> way forward once we correct the mistake of not having a version
> number in the file format that tells the updated clients to ignore
> the generation numbers.  For longer term viability, we should pick
> something that is immutable, reproducible, computable with minimum
> input---all of which would lead to being incrementally computable, I
> would think.

I think it depends on what we mean by backwards compatibility. None of
our docs are saying this is experimental right now, just that it's
opt-in like so many other git-config(1) options.

So if we mean breaking backwards compatibility in that we'll write a new
file or clobber the existing one with a version older clients can't use
as an optimization, fine.

But it would be bad to produce a hard error on older clients, but
avoiding that seems as easy as just creating a "commit-graph2" file in
.git/objects/info/.

  parent reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-29 16:55 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
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 [this message]
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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