Thursday, March 3, 2011

Gomez - Data summary information may be incorrect

If you have used Gomez tool for last mile performance testing, you may have noticed that metrics on Test Breakdown(Data Summary) page does not add up. In the image below you will notice that the time to first byte (1stByte column) is more than the total page response time(Response Time column).

The way Gomez is calculating these values is by adding up response time of same component in all the requests together. For example, In the above image, the DNS time is 0.144 but if you look at the waterfall chart below, you will notice this time is sum of DNS compoment response time of two requests.

You can also have time to first Byte or content download time to be more than the page resonse time. Therefore, I suggest a caution need to be taken when interpreting results from GOMEZ or even presenting them to someone else.

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