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Re: Is the ability to disable flow control really needed?

From: Fred Akalin <akalin@google.com>
Date: Fri, 21 Jun 2013 16:23:30 -0700
Message-ID: <CANUYc_Q3RFrxP-AcL9cTQqUhGu=bG81ANCpv+pVUVOWCGhgLHw@mail.gmail.com>
To: Martin Thomson <martin.thomson@gmail.com>
Cc: HTTP Working Group <ietf-http-wg@w3.org>
On Fri, Jun 21, 2013 at 3:49 PM, Martin Thomson <martin.thomson@gmail.com>wrote:

> On 21 June 2013 14:58, Fred Akalin <akalin@google.com> wrote:
> > Reading the "Ending Flow Control" section of the spec (3.8.9.4:
> > http://http2.github.io/http2-spec/#EndFlowControl ), I'm wondering if we
> > even need the ability to disable flow control at all.
>
> This is something that we discussed at some length in the Tokyo
> interim.  Getting flow control right is hard.  An implementation will
> screw itself if it doesn't take a great deal of care.  Flow control
> always costs in performance, at best it just costs the bytes for a few
> WINDOW_UPDATE frames; at worst, you end up with lots of periods where
> you receive nothing but silence.  Of course, the upside is that you
> can get good concurrency without spending infinite amounts of RAM.
>
> This is why we included Section 3.6.2:
>
> http://http2.github.io/http2-spec/#rfc.section.3.6.2
>
> Many simple implementations will choose to avoid flow control.  In
> fact, we want to encourage them to avoid implementing it.
>

I agree that flow control is hard, and simple implementations should avoid
it. However, why can't we just recommend to set the initial window size to
2^32-1? Is it a worry that simple clients may end up being used for
not-so-simple tasks like sending large files?
Received on Friday, 21 June 2013 23:23:57 UTC

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