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Re: Connection limits

From: Jamie Lokier <jamie@shareable.org>
Date: Thu, 6 Mar 2008 00:01:09 +0000
To: Mark Nottingham <mnot@yahoo-inc.com>
Cc: "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>
Message-ID: <20080306000109.GD1022@shareable.org>

Mark Nottingham wrote:
>    * resources have been spread across multiple servers, just to work  
> around this limitation

Yes.  Or multiple DNS names to the same server - anyone know if that's
effective at getting more connections?

>    * servers purposefully answer HTTP/1.0, because some clients will  
> use four connections with them

Ooh, that's interesting, thanks.

I have a problem with the 2 connections advice in RFC 2616 (it's
theoretical since I haven't implemented this).  I would like to
produce a web page which is fetching server-driven events using a
"delayed response" model, which needs 3 connections:

    1. One for ordinary content on the page: images etc.

    2. One for the delayed response stream, using the optimal method
       detected for that client.

    3. One for a second delayed response stream used to probe the
       optimal method for that client, without knowledge of specific
       clients, and without knowing the unknowable intermediaries, by
       trying methods which may fail (timeouts, intermediaries
       timeout, intermediaries buffer partial response without
       forwarding, client bugs), and upgrading the primary delayed
       response stream to use better methods when they are detected as
       reliable for this client and its intermediaries.

Should I ever implement this, I will try using multiple DNS names for
the same server and see if that is effective.  If not, I will have to
use multiple IPs as well as multiple DNS names.

More connections are also required for web pages which contain
_multiple_ applications of this style at the same time, running
independently on the same web page (perhaps written by different
vendors), but connecting to the same servers.

> Also, considering the wider availability of event-driven Web servers  
> and intermediaries, resource limitations on servers isn't necessarily  
> the problem it once was.
> What do people think? Should we consider upping this to 4? There's  
> also the possibility of negotiating a higher number of connections hop- 
> by-hop (but that would be outside of HTTPBIS).

If a new revision of HTTP still has a recommended small limit, I think
it would be useful to have a request or response header meaning "don't
count this connection towards the usual limit for the duration of
this request".

I'm under the impression that the 2 connection limit is more
rigorously enforced by IE than Mozilla, as I have seen comments about
needing to work around it in discussions about delayed-GET techniques,
but I haven't tested this.

-- Jamie
Received on Thursday, 6 March 2008 00:01:26 UTC

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