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Incorrect display of "Time to First Byte" in waterfall ?!
12-06-2012, 06:34 PM
Post: #4
RE: Incorrect display of "Time to First Byte" in waterfall ?!
I had a second look at the problem and noticed, that the "Start Offset" seems to affect the confusing display of the waterfall.

Have a look at the attached picture...

I tried to compare the HAR Files from the measurement vs. the HAR File from our server.
Afterwards I tried to understand how the "Start Offset" is calculated.
I think it works like this:

"title":"Run 1, First View for ",

"title":"Run 1, Repeat View for ",
"browser":{"name":"Google Chrome",


(B) –(A) =1.308 sec

If you look at the picture, the TTFB bar at startes exactly at the "Start Offset", which is 1,308 sec.
In our case the "Start Offset" is 0,220 sec and I think the TTFB also is painted from 0,220 sec to 2,371 sec. It looks like the problem is, that because the "Start Offset" is smaller then the value of "connect", the TTFB bar is partly covered by the bars for "Initial Connection" and "SSL Negotiation".
If that is the case, the total time calculated (3394 ms) would be wrong and should be Start-Offset + TTFB = 2371 sec.

What do you think about this?

Thanks in advance.



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RE: Incorrect display of "Time to First Byte" in waterfall ?! - KaiBra - 12-06-2012 06:34 PM

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