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Re: http/2 prioritization/fairness bug with proxies

From: Ashok Kumar <ashokkumar.j@gmail.com>
Date: Fri, 8 Feb 2013 11:20:43 +0530
Message-ID: <CAOeYYRf6V+oh3ZULG1458wLL-YpgzBJbyQEPiqdo5t_snT=aZQ@mail.gmail.com>
To: William Chan (陈智昌) <willchan@chromium.org>
Cc: Poul-Henning Kamp <phk@phk.freebsd.dk>, Ben Niven-Jenkins <ben@niven-jenkins.co.uk>, Amos Jeffries <squid3@treenet.co.nz>, HTTP Working Group <ietf-http-wg@w3.org>
On Feb 4, 2013 8:05 AM, "Amos Jeffries" <squid3
treenet.co.nz <squid3@treenet.co.nz>> wrote:
> Priority 1 - user actioned fetch - requires fast answer
> Priority 2 - background/automated fetch in user-visible window - requires
fast answer but treat as bulk traffic.
> Priority 3 - automated software fetch - treat as low-speed traffic.
> Priority 4 - idle software probe - may drop if necessary.

I still feel fixed priorities have better use, from a server point of view.
The description may need to be tweaked a bit from the user-agent's needs
perspective. A number will always have different meaning from different
clients and server is not best place to guess who is more important.

One tangential question, please spare me if this is not the right place.
How is priority supposed to work from a server's perspective. Let's say
Apache has a MaxClient of 1000. Will it stop accepting normal requests
after it has used up 80% quota and will wait for higher priority requests?
May be a trivial implementation detail but this has been bothering me for
sometime and I thought this might help in deciding how priorities should be

On Tue, Feb 5, 2013 at 7:17 AM, William Chan (陈智昌) <willchan@chromium.org>wrote:

> I'm sorry if I am unclear in any way. Please continue to
> challenge/question my comments/assertions so I can clarify my position
> as appropriate.
> Just to be clear here, I stand by that it's a protocol bug currently.
> I agree with adding more hooks to convey advisory priority semantics.
> That said, "advisory" is open to interpretation. I agree that the
> sender should ultimately be in control of how it orders responses, and
> indeed there are of course many situations where it's best for the
> sender to ignore the advisory priority. Yet, if the advisory priority
> semantics are generally not respected, then clients will not be able
> to rely on them, and will be forced to implement prioritization at a
> higher layer, which suffers from the link underutilization vs
> contention tradeoff I highlighted earlier.
> I appreciate the concern that we're adding complexity by introducing
> new semantics. I am arguing that because the existing mechanisms for
> addressing starvation are suboptimal, we should treat this as a
> protocol bug and thus change the protocol in such a way as to fix this
> problem. My suggestion for doing so was adding new priority "grouping"
> semantics. I am hopeful that these new semantics will not introduce an
> inordinate amount of specification, as the primary idea is that the
> current SPDY priority levels would apply within a "group". I think we
> can come up with a way to define a group that will be relatively easy
> to spec.
> SPDY/4 introduces other prioritization semantics beyond just grouping,
> but I wanted to focus on this one first, as I believe this is a bug
> that we *need* to fix. The other SPDY/4 priority changes are of a
> performance optimization nature, and I believe they will need to be
> justified by data. I have no plans to raise them up in this group
> until we have said data.
> On Tue, Feb 5, 2013 at 5:34 AM, Poul-Henning Kamp <phk@phk.freebsd.dk>
> wrote:
> > Content-Type: text/plain; charset=ISO-8859-1
> > --------
> > In message <42A54D15-0AA3-4172-94F7-E94C86E84D7F@niven-jenkins.co.uk>,
> Ben Nive
> > n-Jenkins writes:
> >
> >>So the idea is the protocol contains enough 'hooks' to sufficiently
> >>express the different priorities between & within groups that folks
> >>would like to express but isn't prescriptive about how anyone uses or
> >>implements different prioritisation, scheduling, etc schemes.
> >
> > That was clearly not how the original poster presented it:
> >
> >         "I consider all those options as suboptimal, and thus
> >         consider this issue to be a protocol bug. Our SPDY/4
> >         prioritization proposal addresses this by [...]"
> >
> > --
> > Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> > phk@FreeBSD.ORG         | TCP/IP since RFC 956
> > FreeBSD committer       | BSD since 4.3-tahoe
> > Never attribute to malice what can adequately be explained by
> incompetence.

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Received on Friday, 8 February 2013 05:51:13 UTC

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