Re: [quicwg/base-drafts] Lessen the divergence from the HTTP/2 prioritization scheme by requiring all PRIORITY frames to be sent on the control stream (#2754)

Robin Marx <> Wed, 05 June 2019 09:07 UTC

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Subject: Re: [quicwg/base-drafts] Lessen the divergence from the HTTP/2 prioritization scheme by requiring all PRIORITY frames to be sent on the control stream (#2754)
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I also think we might be conflating some issues here... to me, streams-depending-on-streams + do we need placeholders is a separate discussion from the original statement of this issue. 

I am a bit hesitant to agree with this proposal, as I am worried about potential HOL blocking on the control stream, see also #2678 (a potential solution which was discarded in London). As mentioned above, this might be rare, but -any- loss on the control stream would impact priorities. Thinking of long fat networks and the CDN/proxy use case (of which it's still a bit unclear if we want to incorporate that into the HTTP/3 prioritization design), this might have a bigger impact than anticipated (though should only be occasional).

I myself was quite happy with just changing default behaviour (with #2690) in the case of potential re-ordering and don't really see the need for this change. The argument that it allows re-introducing exclusive priorities (uttered elsewhere) is true, but as also uttered elsewhere, I don't really see the need for that feature (was only used by Chrome for H2 afaict) and is better replaced with something like "implicit fifo" e.g., #2700 or #2723. 

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