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Re: #540: "jumbo" frames

From: Adrian Cole <adrian.f.cole@gmail.com>
Date: Wed, 25 Jun 2014 07:45:47 -0600
Message-ID: <CAHzwyDvAy3vdgYyJHsqYQq8setXA6k4nTFr4KqKEfkye5ekOmA@mail.gmail.com>
To: Matthew Kerwin <matthew@kerwin.net.au>
Cc: Greg Wilkins <gregw@intalio.com>, Mark Nottingham <mnot@mnot.net>, "K.Morgan@iaea.org" <K.Morgan@iaea.org>, Poul-Henning Kamp <phk@phk.freebsd.dk>, Willy Tarreau <w@1wt.eu>, HTTP Working Group <ietf-http-wg@w3.org>, Martin Dürst <duerst@it.aoyama.ac.jp>
I'll offer another implementer pov.


I'd be personally in favor of a jumbo frame, and am happier with using
a variable length integer encoding to deal with the unbounded nature
of it. Even if variable length integer is a rats nest, I'd prefer we
exhaust more energy on this one before giving up.

Continuations "feel" similar in code to concatenating data frames (to
equal a content length). Except that the latter seems more immediately
sensible as other frames can be interleaved. When you look at how to
statefully (carry end of stream flag, etc) page through continuations
under hpack, it indeed feels complicated and offers little value to
the *code*, basically makes it a spot that bugs are likely to creep
into. Jumbo is simpler, provided we address the length concern, plus
we can always bolt on constraints like a max on that. IOTW, the
framing itself is the more important bit.

Knowing that pinner's in hawaii, I'm sure we'll get at least another
implementer perspective a little later.


On Wed, Jun 25, 2014 at 5:23 AM, Matthew Kerwin <matthew@kerwin.net.au> wrote:
> K.Morgan@iaea.org <K.Morgan@iaea.org> wrote:
>> So barring a change to 64 bits, you need
>> the CONTINUATION hack or the "jumbo
>> frame" hack.  Which hack is better?
> My original motivation for jumbo frames was that I wanted to break
> hpack's blocking behaviour, by only compressing the HEADERS (or PP)
> frame and making each CONTINUATION stand alone. Because some
> individual headers are known to be >16K I needed a way to extend
> CONTINUATION frames (and only them). Thus there'd be only one hack,
> only useful for and only used by folks who insist on sending huge
> headers -- and incidentally easy to detect and apply social
> back-pressure against.
> Where this has gone, it feels to me too much like a hacky workaround
> with too many shortfalls and ragged corners. My opinion is that we
> either bite the bullet and extend the common length field out to N*
> bits (with settings for receiving variable-length frames
> [max_data_length, max_headers_length, max_settings_length?] to keep
> things sane), thus simultaneously fixing your data throughput concerns
> and rendering CONTINUATION unnecessary, or suck it up and keep
> everything the way it is.
> I don't know whether it's better here to bite or suck. I suspect
> people will have opinions.
> *32, 64, whatever -- something everyone considers "big enough" for the
> forseeable future.
> --
>   Matthew Kerwin
>   http://matthew.kerwin.net.au/
Received on Wednesday, 25 June 2014 13:46:15 UTC

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