Concurrent User Calculation

Question

I am trying to calculate the average concurrent user using the below formula

Average Concurrent Users = Visits per hour / (60 min/hour / average visit)

Visit Per Hour is 750

Average Visit is 1.6 Min (The amount of time user will spend to access the use case)

Thus Average Concurrent User comes around 20.

Now I made some performance improvement and the Average Visit comes down to 1.2 minutes. Thus I again use the formula to calculate the Average Concurrent Users, which comes around 15.

Logically when we do any performance improvement the concurrent users should increase rather than decrease. Is there any problem with the calculation.

Answer 1

You are correct. Concurrent user sessions will decrease if the average session time decreases and all else remains the same. This can be a good thing, if users are able to do their business more quickly and get on with their lives.

For performance tuning and capacity planning, measuring concurrent sessions is much less useful than raw requests per second (throughput) and average or median response time (latency).

Think about it this way: when a user is reading a web page they downloaded, the server isn't doing anything. While 1,000 users are reading pages, the server still isn't doing anything. The only parts of a user session that matter are between the click and the response.