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

From: James Simonsen <simonjam@google.com>
Date: Fri, 12 Apr 2013 17:20:21 -0700
Message-ID: <CAPVJQi=qaPjjbyMqret1kFGo92UZPSqr=Atu_bGRZCYn_=4iVA@mail.gmail.com>
To: public-web-perf <public-web-perf@w3.org>
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.


On Fri, Apr 12, 2013 at 4:53 PM, Nic Jansma <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'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...
> - Nichttp://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>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. Note the "site.js loaded in x
>> milliseconds" at the bottom of the page. Browse to the "About" page on
>> 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 00:20:49 UTC

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