Performance and Scalability Matrix

Maximum VUsers per Agent Computer

The following table shows the recommended maximum number of virtual users per agent computer based on the hardware resources of the agent computer and the type of tested web application.

Note: Testing of applications utilizing SSL reduces VUser capacity by 35%. Testing with TrueLog on Error enabled reduces VUser capacity by 30%. Testing a web application using low-level APIs (Web Low Level) increases VUser capacity by 20%.
System OS Web Business App Web Business App with SSL (-35%) TrueLog on Error (-30%) TrueLog on Error with SSL Web Low Level (+20%)
Intel Xeon Quadcore 3 GHz, 16 GB RAM Windows Server 2008 R2 6500 4225 4550 2958 7800
Intel Core i7 Quadcore 2.8 GHz, 8 GB RAM Windows 8.1 6500 4225 4550 2958 7800
Intel Core2 Duo 3 GHz, 4 GB RAM Windows 7 Enterprise 4700 3055 3290 2139 5640
Note: Web Business App uses page-level APIs (HTML/HTTP). Web Low Level uses low-level APIs (HTTP).

VUsers per Cloud Agent

Note: The maximum number of VUsers per cloud-based agent is 1,000 regardless of the type of the tested application.

The following table shows the number of VUsers that can typically be supported per cloud-based agent, based on the type of the tested application.

Application Under Test Supported VUsers per Cloud-Based Agent
Browser-Driven Load Testing 5
Java/.NET 250
Secure Web (SSL) 600
Web 800

Test Parameters

The numbers in the previous tables were determined by using a realistic workload with the following characteristics:

  • The page structure of all requested web pages corresponds to popular public web pages.
  • The average think time between page views for virtual users was 32 seconds.
  • A single virtual user was emulated with four concurrent connections.

As a result, the number of simulated virtual users corresponds to a realistic number of concurrent users accessing a popular web site, providing the following information:

  • Average hits per page: 39
  • Average page size: 130 KB
  • Average think time between pages: 32 sec

Agent Capacity for Web Protocol Virtual Users

Silk Performer determines the capacity of a machine by using a formula that takes the following parameters into consideration:
  • Number of CPUs
  • Number of cores per CPU
  • CPU speed
  • Memory size

The result is the number of virtual users that can execute a web protocol script on an agent machine with the corresponding parameters.

Agent Capacity for Other Virtual User Types

To determine the number of virtual users that can run on a particular agent machine, the number of web protocol virtual users is weighted by a particular factor that depends on the used technology.
Note: For some technologies there is a maximum number of virtual users defined per machine, merely due to OS limitations rather than CPU or memory constraints.