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

From: Fred Akalin <akalin@google.com>
Date: Mon, 24 Jun 2013 00:15:05 -0700
Message-ID: <CANUYc_ToupGqJkgyLZjKjF1uX9upbM7qhYS5ihjZPPv_Tah3RQ@mail.gmail.com>
To: Gabriel Montenegro <Gabriel.Montenegro@microsoft.com>
Cc: Jeff Pinner <jpinner@twitter.com>, William Chan (陈智昌) <willchan@chromium.org>, Roberto Peon <grmocg@gmail.com>, Martin Thomson <martin.thomson@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>
On Sun, Jun 23, 2013 at 11:44 PM, Gabriel Montenegro <
Gabriel.Montenegro@microsoft.com> wrote:

>  I fail to see the issue with the current draft. Did you see section ****
>
> http://http2.github.io/http2-spec/#fc-principles****
>
> ** **
>
> that answer the questions about whether disabling (or doing anything at
> all) on flow control affects one direction or both directions. That section
> clearly states that flow control is unidirectional. Flow control is
> controlled by the receiver. When the receiver turns it off, or sends a
> window update, or whatever, this only affects the incoming direction to the
> receiver. The sender MUST heed whatever the receiver says.****
>
> ** **
>
> Is there something that still needs clarification in that section?
>

I think that section is perfectly clear. However, the section I was looking
at (and the only one that talks about ending flow control) was not. :)
Perhaps it would be better for the text describing the important semantics
of flow control to be in one section together, i.e. 3.6.1, and have 3.8.9
be only about the WINDOW_UPDATE frame itself.

I think having the big knobs to turn off flow control on a per-stream or
> per-connection basis is preferable to “turning off” flow control via the
> chatty and dynamic game of sending window updates to constantly open the
> window.
>

I hardly think that sending a WINDOW_UPDATE frame every 2^30 bytes can be
describes as chatty, especially since in the vast majority of cases the
number of WINDOW_UPDATE frames sent to turn off flow control, either
effectively or with the flag, remains the same (i.e., 1).

At any rate, I think the current mechanism is fine for this implementation
> draft, perhaps with minor clarification.
>

Sure, I think the other implementors and I are on the same page re. how
this works. Perhaps this is something we can resolve for after the
implementation draft.

-- Fred
Received on Monday, 24 June 2013 07:15:32 UTC

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