I’m going to write about increasing the number of transactions to simulate a higher number of Virtual Users. This is a common technique used by performance testers to ‘cheat’ or rather avoid the high costs associated charged by vendors. I recently answered a question on Linkedin and suggested increasing the transaction rate.

I was sent the following message by Jim:

“Saw a reply on here where you suggested increasing no of iterations to increase load… I’m not a big fan of this at all, as it really doesn’t do that, it compresses time instead so for example say I have 200 vusers and they are running 4 iterations per hour each to increase the number of concurrent users I need to double the number of vusers if I double the number of iterations I reduce an 8 hour soak test to 4 hours I know it’s a commonly used technique, but it’s total rubbish, usually when I hear people saying this I just mention the word “sessions” and their head explodes with the thought: huge amounts of what I’ve done for years is wrong!!!”

Being called out and made to think is good thing.

Now I’m not going to go on the defensive and pick holes – In essence what Jim is saying is correct*, and Jim’s response got me thinking. What on earth is the impact of ‘sessions’, what exactly are they? What is the overhead? Session is an umbrella term people use regularly but I suspect many actually don’t have a firm understanding of it. So I did a little digging.