Peak hour Scenario

In my day by day experience as consultant I meet a lot of IT managers which thinks about performance tests like stressing the system till it does not respond anymore to the load.

This is an interesting and useful approach of course but it is not realistic and most of the time is meaningless. We have to face the reality of the IT projects: they are always late and PT is always planned in the very last stage, most of the times few days before going live. This implies that you have a "challenging" timeframe and you have to make the best of your time.

Actually I suggest to approach the Performance Test starting with the Peak Hour Test. This particular stress scenario is designed to emulate the worst load situation that a web-site/ application will face in its exercise-life.  To test in this condition means that you are not looking for the "failure" point but that you are verifying that your infrastructure can handle the "forecasted" load.

  

In order to do this the application's "owner" should be able to tell which is the worst, real, situation for the application. I say "should be able" because surprisingly very often nobody has a clear answer to this question.  It's like if an airport designer does not know which is the wind in the airport's area or a designer of a dam does not know the level of the water in the reservoir.

Assuming that the peak hour load can be described in terms of concurrent users and frequency of operations my suggestion is to add a little bit more (10%) of the load and use this as load scenario!! 

This test is called the peak hour test and is in my opinion the best test to be done if you have limited budget and time constraints. It tells you if your application can "work" and how it responds in the worst working condition. By reaching the failure point you only know which is the total load. You do not have a clear picture of what would be the user experience. Furthermore the application's tuning has to be done in the "operation" range and not in the failure zone.