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Re: [Resource Timing] Definition of "network layer cache"

From: Nic Jansma <nic@nicj.net>
Date: Fri, 12 Apr 2013 19:53:02 -0400
Message-ID: <51689E5E.3000507@nicj.net>
To: "William Chan (陈智昌)" <willchan@chromium.org>
CC: James Simonsen <simonjam@google.com>, public-web-perf <public-web-perf@w3.org>
I seem to remember "networking layer cache" being somewhat intentionally 
left vague, as we figured different UAs would have various caches and we 
didn't want to pigeon hole what it meant.

Outside of what the phrase "networking layer cache" means, the intent 
was to include all resources included in the page, regardless of whether 
a request went out over the network to get them.  In this case, site.js 
is included statically in webpagetest.org's HTML:

<script type="text/javascript" 
src="http://cdn.webpagetest.org/js/site.js?v=28"></script>

I would expect/hope site.js would be included as a PerformanceEntry in 
the PerformanceTimeline, even if it was "cached" from the previous page 
load. It's load time would be near 0, since it was loaded from whatever 
caches the UA has.

The wording around "networking layer cache" could certainly be better 
explained, but I'm not sure how...

- Nic
http://nicj.net/
@NicJ

On 4/12/2013 6:54 PM, William Chan (陈智昌) wrote:
> I think "network layer cache" should be redefined in such a way to 
> make Blink's behavior incompliant. The Blink memory cache is just 
> another cache in the cache hierarchy.
>
>
> On Fri, Apr 12, 2013 at 3:40 PM, James Simonsen <simonjam@google.com 
> <mailto:simonjam@google.com>> wrote:
>
>     The Resource Timing spec says:
>
>     "Resources that are retrieved from the user agent's networking
>     layer cache must be included as PerformanceResourceTiming objects
>     in the Performance Timeline."
>
>     What exactly constitutes a "networking layer cache?" Blink's
>     memory cache seems to behave differently than IE10's. When
>     navigating pages on the same site, Blink uses the "in-memory
>     cache" and reuses subresources without fetching. That means we
>     don't report Resource Timing for these resources. IE10 seems to
>     always report resources in the same circumstances.
>
>     To try it out, visit webpagetest.org <http://webpagetest.org>.
>     Note the "site.js loaded in x milliseconds" at the bottom of the
>     page. Browse to the "About" page on webpagetest.org
>     <http://webpagetest.org>. That message disappears on Chrome, it
>     shows a new value on IE10.
>
>     Are we both compliant in our own ways? Or do we need to better
>     define "network layer cache?"
>
>     James
>
>
Received on Friday, 12 April 2013 23:51:59 UTC

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