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

From: Nic Jansma <nic@nicj.net>
Date: Fri, 12 Apr 2013 21:40:51 -0400
Message-ID: <5168B7A3.3040600@nicj.net>
To: James Simonsen <simonjam@google.com>
CC: public-web-perf <public-web-perf@w3.org>
Awesome, that's a great simplification -- it describes what we were 
originally intending.  i.e. what one would see in Firebug/F12/DevTools.

- Nic

On 4/12/2013 8:20 PM, James Simonsen wrote:
> I agree that seems like the desired behavior and that we need to say 
> that more clearly.
> Should we totally change the processing model? For instance:
> 1. If the resource is fetched from the network, log it.
> 2. If it's fetched from a local cache, and the resource hasn't been 
> seen before, log it and record it in a "set of seen resources."
> 3. If it's fetched from a local cache, and the resource is already in 
> the "set of seen resources," abort these steps.
> Obviously, I wouldn't expect anyone to actually implement that set, 
> but it at least makes the processing model convey what we want.
> James
> On Fri, Apr 12, 2013 at 4:53 PM, Nic Jansma <nic@nicj.net 
> <mailto:nic@nicj.net>> wrote:
>     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 <http://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 (ι™ˆζ™Ίζ˜Œ) 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 Saturday, 13 April 2013 01:39:46 UTC

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