Device calibration is performed to calculate the optimal Payload value for the number of virtual users per Load Injector Server. The device complexity and required CPU resources are considered during calibration. Calibrated Payload value ensures LI Server CPU load no more than optimal 60-80% and provides the maximum load distribution among the LI Servers.

Calibrated Payload varies based on a task type:

  • HTTP(S) Test: from 500 to 1000 users
  • Web Page/Streaming Media/Web Application Test: from 8 to 25 users
  • Postman Collection Test: from 20 to 100 users

User Delay Impact on Calibration Results

While calibration we calculate how much load the simulation of one virtual user puts on a LI Server. If there are no user delays set, a LI constantly runs a test session in a loop without delays between the test sessions, thereby increasing its CPU usage. For example, CPU usage can reach 100% while executing a very fast API call.

On the other hand, if a user delay is set in the User Behavior profile, a LI Server will be idle during the delay time period. In this case, CPU utilization will be lower than for the same test execution without user delays. Thus, more virtual users can be generated by a LI without an increase in CPU load.

Considering this, the longer a user delay time set for a test, the higher payload value you will receive as a result of a device calibration.