- From: McCall, Mike <mmccall@akamai.com>
- Date: Tue, 9 Oct 2012 15:22:41 -0400
- To: public-web-perf <public-web-perf@w3.org>
Hi web-perf, I just wanted to give some feedback on the Navigation Timing 2 draft. After reading the spec, it appears that a big change has been made to the interface and how it reports timestamps. In particular, it looks like navigationStart will always be 0.000, and everything will be reported as a delta from that time. If this is in fact, correct, then I am concerned that by not having an absolute timestamp available, it will be difficult to correlate Navigation Timing measurements with backend logs, which can be useful for postmortem debugging. Perhaps an additional attribute could be added, 'navigationStartTimeStamp' for example, which would contain the epoch time of navigationStart. To be clear, I don't think we need an epoch timestamp for every attribute, but knowing the timestamp from which the measurements are based would be useful. Also, I noticed that the concept of first paint/pixel is omitted in this draft. While IE supports it with a vendor prefix, and Chrome exposes it through their window.chrome.loadTimes() object (not sure if other browsers expose it), it would be good if it were included as part of the official spec so there was a browser-independent place to gather this data. Some 3rd-party testing vendors including webpagetest.org, report some concept of the time the browser began rendering the page, and I think it would be valuable here too. Finally, based only on the spec, it seems difficult to determine whether or not the document was retrieved from cache or not. Is it possible to determine that a document was not downloaded from the server, but retrieved from cache, via the Navigation Timing API? If not, would a 'fetchType' attribute be useful here? Mike
Received on Wednesday, 10 October 2012 15:47:49 UTC