To determine the required number of load generators:
Record a script using a protocol
Replay a single Vuser in Controller and check the average CPU and the peak memory consumption of the mdrv.exe process by adding a counter for % Processor Time and Private Bytes.
Based on your load generator hardware and the CPU and memory consumption of a single Vuser, calculate the number of Vusers per machine.
For example:
Let us assume that each of the load generators has 8 core processors and 16GB of memory. Let us also assume that a single Vuser consumes 100MB of peak memory and 10% CPU on average for the specific business process.
From a CPU perspective:
If we limit the CPU consumption up to 70% utilization, we can have 7 Vusers per core processor (70% /10%). If our load generator has a total of 8 cores processors, 8 * 7 Vusers per processor equals 56 Vusers per load generator.
From a memory perspective:
The load generator machine has the 16GB memory of which 15GB is available for the Vusers so approximately 150 Vusers per load generator machine (15GB / 100MB). Around down the near whole number as we can't run part of the Vuser.
Therefore, to meet both the CPU and memory capacity limits, we use the lower number of Vusers and we calculate that for this business process, we can run approximately 56 Vusers per load generator.
