I was recently helping a colleague to highlight how good some transaction response times were. However his graphs were plagued with the odd "spike" where a response time was really bad, i.e from 1.4 seconds average up to a 90+ second spike.

This made the transaction response time graph look bad and would have cause the reader of the report to focus on the spikes instead of the averages.

Instead a transaction response time distribution graph was used, this highlights a count just how many transaction had a particular response time:



The graph is much easier to talk about since the readers ear is immediately (and rightly so) drawn to the the "big number".

What I'm wondering about now is - why are there two clear groups of slow transactions? Between 46 to 58 seconds and 76 to 98 seconds. I've heard about defect clustering - but slow transaction clustering sounds strange.... but they are clustered.