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Question about HTTP 2.0 priority

From: Chad Austin <caustin@gmail.com>
Date: Wed, 1 Oct 2014 18:12:36 -0700
Message-ID: <CA+dRvWhbY8DQFy+4RycJPwLoHa4ictZR90FENRKE6Y85PDZPHQ@mail.gmail.com>
To: ietf-http-wg@w3.org
Hi,

I am reading the HTTP 2.0 draft, and I wonder whether HTTP 2.0 supports
implementing simple stream priorities like SPDY does.

Our use case is documented in detail at
http://chadaustin.me/2014/08/web-platform-limitations-xmlhttprequest-priority/
, but I will summarize here.

We have a whole pile of 3D assets that we need to retrieve from various
URLs and load into WebGL.  Some of them are higher-priority than others.
None of them depend on any other.  For example, we may want to prioritize
resources closer to the camera.  We definitely want to prioritize meshes
and low-resolution textures over high-resolution textures and animation
files.

Ideally, our application would immediately issue ALL requests and let the
browser's network stack (and HTTP/SPDY/HTTP2 backend) efficiently utilize
the socket(s) and bandwidth to transfer high-priority assets before
low-priority assets.  However, if there is available bandwidth, we would
benefit from receiving low-priority assets in the meantime.

We would benefit from a large number of priority bits, but could make it
work with as low as 3 bits.  (2 bits would be too few.)

How do I map that use case to HTTP 2.0's dependency graph?  At first blush,
it seems hard: I'd have to define a stream per priority level, and set
dependencies such that all low-priority streams depend on high-priority
streams?  And if a high-priority stream finishes, then reset the dependency
to another high-priority stream?

-- 
Chad Austin
http://chadaustin.me
Received on Thursday, 2 October 2014 01:13:04 UTC

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