WASP - Generator

A Generator is a component that encapsulates all the characteristics of load generation, including:

• Load type:
  • RPS (requests per second)
  • VUs (virtual users)
• Load schedule
• Call logic
• Response data
• Sampling
• Timeouts

Choosing Between Gun and VirtualUser

Gun

• Best for stateless protocols (e.g., HTTP).
• Simplistic in nature; ideal for executing a single operation that does not require setup or teardown.
• Operates using an open model, where:
  • The number of requests is fixed.
  • The load adjusts to meet the target RPS, regardless of the system's response time.
  • There's no feedback from the system.
• Recommended for scenarios focused on measuring throughput.

VirtualUser

• Designed for stateful protocols (e.g., WebSocket) or workflows involving multiple operations (e.g., authenticating, executing tasks, and logging out).
• More complex, with dedicated methods for setup and teardown.
• Operates using a closed model, where:
  • New iterations start only after the previous one completes.
  • The RPS fluctuates based on the system's response time. Longer response times reduce RPS.
  • Feedback from the system is used to adjust the load.

Closed vs. Open Models

• A Gun follows an open model:

  • It controls the rate of requests being sent.
  • The system's response time does not impact the load generation rate.

• A VirtualUser follows a closed model:

  • It controls the rate of receiving responses.
  • The system's response time directly impacts the load generation rate. If the system slows down, iterations take longer, reducing the RPS.

Summary

In simpler terms:

• A Gun limits the load during the sending phase, making it ideal for throughput measurements.
• A VirtualUser limits the load during the receiving phase, reflecting the system's performance under load.

This distinction helps you decide which tool to use based on the protocol type and the goals of your test.