Re: h2 priority

Hi Patrick,

Sorry, I almost missed this one in the noise ...

On Sep 2, 2014, at 8:28 AM, Patrick McManus wrote:
> On Sun, Aug 31, 2014 at 7:06 PM, Roy T. Fielding <fielding@gbiv.com> wrote:
> 
> 
> The reason I did not go into any more detail than that is because the
> priority information is only a suggestion, like in h2.  Defining how
> the recipient is going to reprioritize its stack based on existing
> streams is an implementation detail behind the HTTP interface: wishful
> thinking and untestable (because it is only a suggestion).  Editorially,
> section 5.3 belongs in an appendix, or as a separate spec that has time
> to ruminate on the balance between weighted streams and various
> response characteristics.
> 
> Editorially and organizationally I think you're right but am happy to defer to the editor. As a matter of content, I think the fairly complicated scheme is well justified in terms of identified problems spdy has shown with using just a few bits of weight (aggregation of lots of clients, dash like dependencies, etc..)

Does that mean it has been implemented?  I mean, does the weighted tree
with stream dependencies result in effective prioritization by a server?

I am curious about that because I see most UA traffic as parallel with
aborts, rather than dependent streams, and expect a user agent to prioritize
by fairly well-understood latency buckets (critical path, js, renderable
content, not-rendered-yet content, background prefetch, long pull, etc.).
IOW, I don't see how a client can guess which streams are "more important"
other than by the perceived latency buckets.

> > 6.2.  HEADERS
> >
> Priority is a suggestion.
> 
> imo it is only really a suggestion in the sense that it is untestable. Priority is a core piece of h2, because h2 introduces mux and a non-prioritized mux is worse than h1.

Well, worse than h1 + multiple connections.  Yes, that's why I thought
priority would be important as well.  What I found disconcerting
is that the spec takes a deep dive into explaining how priorities work,
before it even defines the frames, and yet doesn't actually use any of
that stuff in examples or later prose.

....Roy