RE: [ResourceTiming] A few small things

Nic,

The spec text matches our intentions. The startTime is defined as the time immediately before the user agent starts to queue the resource for fetching and the fetchStart is defined as the time immediately before the user agent starts to fetch the resource, for the very reasons described in section 1 of your mail.

Thanks,
Jatinder

From: public-web-perf-request@w3.org [mailto:public-web-perf-request@w3.org] On Behalf Of Nic Jansma
Sent: Tuesday, September 13, 2011 2:44 PM
To: public-web-perf@w3.org
Subject: [ResourceTiming] A few small things

Hi folks,

A few thoughts about the current draft @ http://www.w3c-test.org/webperf/specs/ResourceTiming/

1. We've discussed the differences between ResourceTiming's startTime<http://www.w3c-test.org/webperf/specs/ResourceTiming/#performance-resource-timing> and fetchStart<http://www.w3c-test.org/webperf/specs/ResourceTiming/#fetch-start> before, but I think there is still a bit of confusion.  Ignoring redirects for a moment, startTime is currently defined as "The startTime attribute must return the time immediately before the user agent starts to queue the resource for fetching".  In a recent discussion with James [1], we talked about startTime always equaling fetchStart for non-redirection scenarios.  However, we had also previously talked about startTime possibly being earlier than fetchStart, in the case that the browser queued a resource for download but does not immediately attempt to fetch it because of connection limits.  For example, if you included 100 <img>s all on the same domain, the resources may all have a similar startTime (parsing HTML is fast), but their fetchStarts would differ on the later <img>s as connections became available.  I believe the wording of startTime in the spec currently supports this notion, but I wanted to make sure everyone agreed that was the intention?

2. For consistency, can we rename INITIATOR_IMAGE<http://www.w3c-test.org/webperf/specs/ResourceTiming/#sec-window.performance-attribute> to INITIATOR _IMG?  All of the other initiator names use the HTML element name or concept, and IMAGE seems a bit ambiguous when it really only means the <IMG> tag.

3.  The most popular initiator<http://www.w3c-test.org/webperf/specs/ResourceTiming/#sec-window.performance-attribute> that I see on the web that currently falls under INITIATOR_OTHER is input[type='image'].  The second most popular is body[background='...'].  We could add INITIATOR_INPUT and INITIATOR_BODY, though I don't feel strongly that we need them.

- Nic

[1] [Resource Timing] Spec feedback, dated Wed 8/31/2011 12:50 PM