Concurrent User calculation for Testing
In the NFR that is given to us, we have SLA for response times and throughput. The number for users for which the test needs to be carried out is not mentioned.
Is it possible to apply Little's law to calculate the number of users or is there other way to calculate the number of users.
Little's law emphasizes transaction rate over sessions. This is a difference between a well which holds a defined amount of water with a very small impact on the surface for the opening of a well and a very large shallow lake with the same amount of water, but provides very different stress on the surface of the earth from the weight of the water (sessions).
Originally Posted by Gyami
If you want an objective number then go to the current production version of the application and take a look at the request logs. You should find a set of IP addresses here which correspond to the unique number of users. This way you can look at the time between first and last request for a given IP address (grouped by hour) to determine what your typical live request session duration is. This value is likely different than the number you see in a session console due to session timeout.
Once you understand your live request session duration then you can use that as a blocking interval to count the number of distinct hosts/IP addresses in a given block. This will provide an objective , verifiable set of data on how many users are on your system at any given point. The longer the period of your logs the greater an opportunity you have to identify the peak of the peak for reproduction of your load.