Tuesday, October 8, 2013

Vuser Calculation In LoadRunner

How to calculate number of virtual users (VUsers) for load/stress testing? What should be the concurrent virtual users to load?

 What should be the peak load?

25, 100, 500, 1000. We cannot give number of VUsers blindly which will not return intuitive result for analysis.

The main purpose of VUsers is to simulate the live environment. It is very tricky but easy to obtain number of VUsers required for the load/stress testing. Universal formula to calculate the arriving rate to the system is Little’s Law.

N = Z * (R + T)

where 

N – number of VUsers,
Z – Transactions per Second (TPS)
R – Response Time in seconds
T – Think Time in seconds

If you get the following data from the stakeholders i.e. TPS, Response Time and Think Time, number of VUsers can be calculated easily.

E.g. 

TPS is 100, R is 3 sec and T is 2 sec then N will be

N = 100 * (3+2)
= 100 * 5
= 500

Peak load will be 500 VUsers.

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