From: Jeff King <peff@peff.net>
Date: Thu, 17 Mar 2011 07:15:12 GMT
Subject: Re: [PATCH 1/2] fetch-pack: Finish negotation if remote replies "ACK %s ready"
Message-ID: <20110317071512.GF11931@sigill.intra.peff.net>
In-Reply-To: <1300146519-26508-1-git-send-email-spearce@spearce.org>

On Mon, Mar 14, 2011 at 04:48:38PM -0700, Shawn O. Pearce wrote:

> Upon receiving "ACK %s ready" there is no point in looking at
> the remaining commits inside of rev_list.  Sending additional
> "have %s" lines to the remote will not construct a smaller pack.
> It is unlikely a commit older than the current cut point will have
> a better delta base than the cut point itself has.
> [...]
> Assuming the client is only following the remote (and does not make
> its own local commits), the client needs 11 rounds to spin through
> the entire list of tags (32 commits per round, ceil(339/32) == 11).
> Unfortunately the server knows on the first "have %s" line that
> it can produce a good pack, and does not need to see the remaining
> 320 tags in the other 10 rounds.

Does this optimization help in that case? From looking at the code, it
seems that we offer "ACK %s ready" only in the case that the client
has something we do not. I.e., they _are_ building local commits on top.

> Over smart HTTP, the client must do an additional 10 HTTP POST
> requests, each of which incurs round-trip latency, and must upload
> the entire state vector of all known common objects.  On the final
> POST request, this is 16 KiB worth of data.

This optimization aside, I wonder if it is worth bumping up the number
of haves we send in a chunk from 32 to something higher.

-Peff