Subject: Re: pack negotiation algorithm between 2 share-nothing repos

From: Junio C Hamano <[email-masked]>
Date: Wed, 26 Aug 2015 09:49:56 -0700

Junio C Hamano <[email-masked]> writes:

> Duy Nguyen <[email-masked]> writes:
>
>> I know this is a corner case, but because it has a valid use case,
>> maybe we should do something about it. Immediate reaction is to add an
>> option to send no "have"s. But maybe you guys have better ideas.
>
> This and similar corner cases were discussed in very early days of
> Git.
>
> One interesting idea floated back then but was not pursued was to
> dig and send have's sparsely and then back up.  Instead of digging
> and sending _all_ commits in a contiguous history, after sending the
> tip, you skip the commits from the history before sending the next
> one, and progressively make the skipping larger (e.g. Fibonacci, or
> exponential).  You need to remember what you sent and for each of
> what you sent its topologically-oldest descendant you sent earlier
> that you heard the other side does not have.
>
> Then, when you get an Ack, you know a stretch of history between a
> commit that is known to be common (i.e. the one you heard an Ack
> just now) and its descendant that is known only to you (i.e. the
> topologically-oldest one you remember that you did send and they
> didn't say is common).  At that point, you and the other end can
> bisect that range.

If anybody is interested, here is a good place to start:

http://thread.gmane.org/gmane.comp.version-control.git/96149/focus=102485

[Cc'ed Stefan as I think he was collecting possible enhancement to
put in the protocol v2].