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Re: [NavigationTiming2] Comments and questions about the Navigation Timing 2 draft

From: Reitbauer, Alois <Alois.Reitbauer@compuware.com>
Date: Thu, 11 Oct 2012 18:44:22 +0000
To: "McCall, Mike" <mmccall@akamai.com>
CC: "public-web-perf@w3.org" <public-web-perf@w3.org>
Message-ID: <CC9CDE62.186B5%alois.reitbauer@compuware.com>

On 10/11/12 5:19 PM, "McCall, Mike" <mmccall@akamai.com> wrote:

>On 10/11/12 4:05 AM, "Reitbauer, Alois" <Alois.Reitbauer@compuware.com>
>>Navigation Start and Clock Sync:
>>You should not use the clock time of a machine to sync with your server
>>clock directly.
>I agree that it's not wise to rely on a client's clock being in sync with
>the server's, but for the purposes of post-mortem analysis, not having a
>timestamp when a Navigation Timing measurement was taken is worse than a
>slightly (or perhaps in the odd case, wholly) incorrect one. I would
>imagine that one of the primary use cases of Navigation Timing is to
>collect and beacon the data back to a central server for analysis.  Being
>able to correlate, however roughly, when the server interacted with the
>client is a good thing in my opinion.

[Alois] You could also use the NavTiming 1 values for this :-). Maybe the
first timestamp could also be represented as an absolute value.

>>First Paint/Pixel:
>>There was already a lot of discussion about this. My question is what
>>this value tell you?
>I am actually rather intrigued by the amount of discussion this has
>caused, and thank Boris, Ilya, and you for enlightening me on the subject.
> As Ilya pointed out, I fall into the large category of people who
>consider firstPaint to be when "the user sees something".  It's true that
>hardware capabilities may stand in the way of getting an exact value of
>this, but at least understanding when the user agent /told/ the hardware
>to start painting is a good start.  We can work on instrumenting hardware
>in NavTiming 3. :)

[Alois] Ok, so a discussion about other useful lifecycle metrics that are
more related to the end user make sense. I think there is more than first
paint then, however.

>>This is highly specific to the actual page. I
>>personally work a lot with ResponseStart (First Byte Time - kind of),
>>DocumentContentLoaded (all html is there) and DomComplete (all dom
>>elements loaded). This combination tells me a lot of the lifecycle of the
>This is true, and this level of insight into the document's lifecycle is
>amazing.  However, understanding when the user saw something gives an even
>clearer picture of the document's lifecycle, since there are many things
>that may slow down or interrupt the processing of the DOM throughout the
>domLoading->domInteractive->domContentLoaded->domComplete chain.  In
>addition, many front-end optimization techniques actively try to improve
>the time to a user "seeing something", and being able to quantify that for
>real users is valuable.

[Alois] I think the value of this "something" should be verified across a
huge number of pages. I know that tools try to optimize this, but what if
it is a blank screen. What I saw people doing is defining which parts of
the document have to be loaded so that the page can be considered
"visible" for the user.

>>Caching Information:
>>This would in fact be cool information. The reason this was dropped was
>>because of privacy reasons. However calculating ResponseStart -
>>RequestStart should do the trick.
>I suppose I understand the privacy concern from a Resource Timing
>perspective, but I don't necessarily understand it here, especially since
>it can be inferred.  Can someone explain?

[Alois] Would be worth another discussion. I think this is about other
JavaScript from widgets that could also figure out if you have been to a
site before.


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Received on Thursday, 11 October 2012 18:44:58 UTC

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