W3C home > Mailing lists > Public > ietf-http-wg@w3.org > January to March 2014

Re: BLOCKED frame.

From: Martin Thomson <martin.thomson@gmail.com>
Date: Sun, 26 Jan 2014 13:27:51 -0800
Message-ID: <CABkgnnUDA9CO-Sia7+Txt1UxLmGpNPEr7eYbgz9r7GN2zSMDuw@mail.gmail.com>
To: Mike Belshe <mike@belshe.com>
Cc: Roberto Peon <grmocg@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>
I'm not sure about redundant, but I'm certainly not that excited by
the idea.  I think that this is going to be very hard to extract
useful information from, and it's probably going to be difficult to
generate properly, let alone interpret.

I can appreciate the value of having an interoperable mechanism for
this sort of reporting channel, but I think that it's probably better
to build this sort of feedback into a specialized tool, rather the
protocol itself.  There are plenty of sites out there that test how
good your site/server/client is with respect to various aspects of
HTTP, web performance and so forth and I don't think that this is any
different from those.  The incremental gain seems minor, but a
protocol element, particularly at this stage, is expensive.

On 25 January 2014 05:33, Mike Belshe <mike@belshe.com> wrote:
> Questions:
>   - is there any existing implementation experience with BLOCKED?
>   - Why can't each side already infer blocked based on the window size being
> closed?  (I do realize the max-conns-reached case could benefit, but I think
> that is less valuable)
>
> I ask because the definition seems unclear.  "When an endpoint is blocked on
> flow control, but the socket is writable".  What exactly does this mean?
> If the socket is not writable for 60 seconds, do you send BLOCKED once or
> more than once?
>
> Example 1:
>    - the server has sent a WINDOW_UPDATE, but it is in flight
>    - client flushes enough data that there is 1 byte of space in the socket
> buffer
>    - send a BLOCKED frame?
>
> Example 2:
>    - server sets window to 64KB
>    - client has 65KB to send, so it sends 64KB bytes followed by a BLOCKED?
>
> Example 3:
>    - server sets window to 1024 bytes
>    - client immediately sends a BLOCKED
>    - 3 seconds later, you're still blocked, do you send BLOCKED again?
>
> Example 4: (perhaps a chatty version of example 1)
>    - server sends WINDOW_UPDATE opening 1 frame of space (1400bytes)
>    - client sends 1400 bytes
>    - client sends BLOCKED
>     - server sends WINDOW_UPDATE opening 1 frame of space (1400bytes)
>    - client sends 1400 bytes
>    - client sends BLOCKED
>    - server sends WINDOW_UPDATE opening 1 frame of space (1400bytes)
>    - client sends 1400 bytes
>    - client sends BLOCKED
>
>
> Overall, I must be misunderstanding, because I think the blocked frame is
> redundant?
>
> Mike
>
>
>
>
>
>
> On Fri, Jan 24, 2014 at 6:11 PM, Roberto Peon <grmocg@gmail.com> wrote:
>>
>> I added a new issue for the blocked frame.
>>
>> As a reminder, the expectation, based on our implementation experience, is
>> that flow control and other settings limiting state size are helpful, but
>> can cause issues with the user experience when tuned improperly, as these
>> settings invariably are...
>> Worse, finding bugs in flow control implementations is extremely annoying
>> and difficult without explicit signaling (Why did the client/server stop
>> sending us data? What is going on?!)
>>
>> A BLOCKED frame helps with both of these issues:
>> When an endpoint is blocked on flow control, but the socket is writable,
>> it emits a frame saying so, and the remote end now has explicit signaling
>> about the tuning of the flow control size.
>> When you get a BLOCKED frame, if you didn't expect the other side to be
>> blocked (i.e. you believe the window isn't closed), you can log the fact for
>> investigation.
>>
>> Flow control is the current most-common (and arguably the most important)
>> use for BLOCKED, but an endpoint can also be blocked on the max-concurrency
>> limit, e.g. 10 max connections for gmail. It would be extremely helpful to
>> know how often this is occurring so as to tune these parameters.
>>
>> -=R
>
>
Received on Sunday, 26 January 2014 21:28:23 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 17:14:23 UTC