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Re: Fragmentation for headers: why jumbo != continuation.

From: Mark Nottingham <mnot@mnot.net>
Date: Fri, 11 Jul 2014 15:57:20 +1000
Cc: Willy Tarreau <w@1wt.eu>, Roberto Peon <grmocg@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>
Message-Id: <0BD19BA6-1C9F-4CDA-9F64-1A30701C0B64@mnot.net>
To: Greg Wilkins <gregw@intalio.com>

On 11 Jul 2014, at 3:50 pm, Greg Wilkins <gregw@intalio.com> wrote:

> 
> On 11 July 2014 15:32, Mark Nottingham <mnot@mnot.net> wrote:
> Roberto isn't making a latency argument -- it's an argument for minimal buffering in the optimistic case(s).
> 
> 
> Servers have to hold the headers for the entire request handling duration anyway (unless you throw away all the general purpose servers that we currently have), so it makes no difference to their buffering if the headers arrive in 1 or many fragments.
> 
> Proxies cannot forward headers in fragments because:
> 	 the routing information may be in the last fragment.
> 	 because encoding mutates the ref set, a proxy cannot commence sending headers until it has all fragments, else it risks blocking the whole connection.
> Getting rid of the ReferenceSet may fix 2 and help with 1 in special cases.  

Roberto appears to be arguing that just because the routing information might be in the last fragment, it isn't always; that's pessimistic. If the necessary information is in the first, it can be acted upon and then forwarded, reducing the buffers necessary to serve this more optimistic case.

Likewise, on the response side, an intermediary can pass receive and then send fragments of headers, rather than buffering them.

I'm not taking a position here, BTW -- just trying to clarify the discussion. It also appears to be the crux of the argument regarding getting rid of or keeping CONTINUATION...


> But I maintain that if we really want to fragment headers, then put them in a segment of DATA frames rather than invent a second mechanism.

Greg, you appear to be alone here...

Cheers,

--
Mark Nottingham   https://www.mnot.net/
Received on Friday, 11 July 2014 05:57:51 UTC

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