Re: Mercurial 0.4e vs git network pull

From: Matt Mackall <mpm@selenic.com>
Date: May 16, 2005, 01:12 UTC
Message-ID: <20050516011209.GM5914@waste.org>
In-Reply-To: <428793A1.5070004@pobox.com>

On Sun, May 15, 2005 at 02:23:29PM -0400, Jeff Garzik wrote:

Show 25 quoted lines

> Matt Mackall wrote:
> >On Sun, May 15, 2005 at 04:22:19AM -0700, Adam J. Richter wrote:
> >
> >>On Sun, 15 May 2005 10:54:05 +0200, Petr Baudis wrote:
> >>
> >>>Dear diary, on Thu, May 12, 2005 at 10:57:35PM CEST, I got a letter
> >>>where Matt Mackall <mpm@selenic.com> told me that...
> >>>
> >>>>Does this need an HTTP request (and round trip) per object? It appears
> >>>>to. That's 2200 requests/round trips for my 800 patch benchmark.
> >>
> >>>Yes it does. On the other side, it needs no server-side CGI. But I guess
> >>>it should be pretty easy to write some kind of server-side CGI streamer,
> >>>and it would then easily take just a single HTTP request (telling the
> >>>server the commit ID and receiving back all the objects).
> >>
> >>	I don't understand what was wrong with Jeff Garzik's previous
> >>suggestion of using http/1.1 pipelining to coalesce the round trips.
> >
> >
> >You can't do pipelining if you can't look ahead far enough to fill the 
> >pipe.
> 
> Even if you cannot fill a pipeline, HTTP/1.1 is sufficiently useful 
> simply by removing the per-request connection overhead.

Sure. It cuts round trips by a factor of 2. But that's just about all it does.

Mercurial already does:
  - approximately O(log(new changesets)) requests/data to find new changesets
  - one request to get an entire changegroup (set of all new
    changesets), which comes back all nicely pipelined and sorted by file
  - delta transfer

In "dumb http" mode, ie what's been there since about day three, it
can do:
  - one request (size proportional to total number of changesets) to
    find new changesets
  - approximately two requests per changed file to pull all deltas
    (vs request per file revision)
  - delta transfer

-- 
Mathematics is the supreme nostalgia of our time.