Re: Is anyone working on a next-gen Git protocol?

[Junio C Hamano <gitster@pobox.com>]

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

> On Wed, Oct 3, 2012 at 9:13 PM, Junio C Hamano <gitster@pobox.com> wrote:
>> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>>
>>> I'm creating a system where a lot of remotes constantly fetch from a
>>> central repository for deployment purposes, but I've noticed that even
>>> with a remote.$name.fetch configuration to only get certain refs a
>>> "git fetch" will still call git-upload pack which will provide a list
>>> of all references.
>>
>> It has been observed that the sender has to advertise megabytes of
>> refs because it has to speak first before knowing what the receiver
>> wants, even when the receiver is interested in getting updates from
>> only one of them, or worse yet, when the receiver is only trying to
>> peek the ref it is interested has been updated.
>
> Has anyone started working on a next-gen Git protocol as a result of
> this discussion?

I and Shawn helped privately somebody from Gerrit circle, where the
initial ref advertisement is a huge problem (primarily because they
add tons of refs to one commit that eventually goes to their
integration branch), to coming up with a problem description and
proposal document to kick-start a discussion some time ago, but not
much has happened since.  Unless I hear from them soonish, I'll send
a cleaned-up version of the draft before I leave for my vacation.

The gist of it is that the current protocol cannot be upgraded in
place because "who speaks first" is not something you can update
with capability, so we would need upload-pack-v2 that lets the
fetching side speak first.

"What is spoken in the first message" is a separate issue, and one
of the things it can address is to allow the ends to reduce the
amount of ref advertisement that ends up not getting used in the
end, but once we allow the fetcher to speak first, we have much
wider possibilities.