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Incorrect display of "Time to First Byte" in waterfall ?!
11-30-2012, 03:13 AM
Post: #1
Incorrect display of "Time to First Byte" in waterfall ?!
Hello!

We would like to measure the responsetimes of a webpage which has been optimized for mobile devices (e.g. iPad).

Currently we use Chrome 23 and a 2.8 Agent which is configured to a certain User-Agent like this (wptdriver.ini):

options='--load-extension="%WPTDIR%\extension" --user-data-dir="%PROFILE%" --user-agent="Mozilla/5.0(iPad; U; CPU
iPhone OS 3_2like Mac OS X; en-us) AppleWebKit/531.21.10 (KHTML, like Gecko) Version/4.0.4 Mobile/7B314
Safari/531.21.10" --no-proxy-server'

Everything works ok and we get proper results.
The only problem we noticed shows up in the corresponding waterfalls:

The size of the bars for the first request does not match the calculated total time of the request. In detail: "The Time to First Byte" bar looks like its size has been shortened by the sum of "Start Offset", "Initial Connection" and "SSL Negotiation" as you can see in the attached picture.

It is quite confusing, because the bars do not represent the measured times anymore.

The problem does not occur when we measure a different (normal) webpage (Chrome)
The problem does not occur when we measure the webpage on weppagetest.org (Chrome)
The problem also occurs when the User-Agent is not set (wptdriver.ini, Chrome)
The problem does not occur, when we measure the webpage using Firefox.


Any ideas what might be the problem?

Thanks in advance for your answer.

Regards,

Kai


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Incorrect display of "Time to First Byte" in waterfall ?! - KaiBra - 11-30-2012 03:13 AM

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