Re: [quicwg/base-drafts] NUM_PLACEHOLDERS MUST NOT be zero (#2753)

Kazuho Oku <> Fri, 31 May 2019 05:11 UTC

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From: Kazuho Oku <>
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Subject: Re: [quicwg/base-drafts] NUM_PLACEHOLDERS MUST NOT be zero (#2753)
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> Currently, only Firefox would be required to change their prioritization scheme if the number of placeholders is 0. Based on information I've seen(ie: the Cloudflare presentation and my own anecdotal experience), it's not clear their use of placeholders is any better than a scheme that does not use them, so I think it's possible Firefox could change their priority scheme and it would be faster.

Fair point. I agree that placeholders becomes no longer a prerequisite for browsers once we bring back the "exclusive" bit (as proposed by #2754).

OTOH, I am still not sure if there is a necessity to diverge from the design we have in HTTP/2 and start requiring clients to take the server's settings into consideration when building a prioritization tree. We currently recommend servers to set `SETTINGS_NUM_PLACEHOLDERS` to some sensible value other than zero, and given that, as I commented in, suggesting server's to ignore placeholder IDs out of the server's advertised range might be a simpler solution.

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