Re: [RFC] Generation Number v2

> 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/.