1189851 - Collect concurrent cache read/revalidation telemetry

Status: NEW

(Core :: Networking: HTTP, defect, P5)

Description

[Honza Bambas (:mayhemer)]

Scenario:
- channel 1 fetches and caches a resumable/re-validable response
- channel 2 requests the same response while channel 1 still writes the cache
- channel 2 can do a concurrent cache read
- but, channel 2 cannot do it from reasons described at [1]
- so, channel 2 abandons concurrent cache read and waits for channel 1 to deliver a complete content to the cache first

This is suboptimal.  One solution is to ignore conditional headers and let the second request simply fully from the cache w/o revalidation.

I don't know if this is a spec violation or not.  Also I want to see how often it happens we get a 200 on a conditional request so close to a previous request on the same URL.  If sufficiently low, I think we could do this optimization and allow concurrent read in this IMO pretty often happening scenario.

Other solution is to allow two requests during nsHttpChannel lifetime.  That's not a really small change, but would allow us to do this optimization w/o any spec violations.


http://hg.mozilla.org/mozilla-central/annotate/e9389ca320ff/netwerk/protocol/http/nsHttpChannel.cpp#l3291

Comment 1

[Firefox Bug Husbandry Bot]

Bulk change to priority: https://bugzilla.mozilla.org/show_bug.cgi?id=1399258