LoadRunner: VUsers, Scripts & Correlation

LoadRunner is a performance/load testing tool (originally Mercury Interactive, now OpenText/Micro Focus) that simulates many concurrent users to measure how an application behaves under load -- response time, throughput, error rate, and resource usage.

Virtual Users (VUsers)

A VUser is a simulated client that replays a recorded/scripted set of actions. Coordinating thousands of VUsers approximates real concurrent traffic in a way manual testing simply cannot.

Vugen: Recording a Script

The Virtual User Generator (Vugen) records real interactions with the application under test -- HTTP requests, UI actions -- and produces a replayable script that testers then enhance before running it at scale.

Parameterization

A recorded script initially has hardcoded values -- e.g. one specific username. Parameterization replaces these with variable data sets so each VUser behaves distinctly, avoiding an unrealistic scenario where every simulated user submits identical requests.

Correlation: Handling Dynamic Values

Recorded scripts capture dynamic server-generated values (session IDs, tokens) as fixed literals at record time. Correlation extracts these dynamically at replay time instead -- without it, a script would replay stale values and fail against a live server.

Think Time

Real users pause between actions -- reading, typing, deciding. Including think time between script steps produces a realistic load pattern instead of a script that hammers the server with zero delay between requests.