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Load Testing using Load Runner
July 17, 2008
Load Runner is a tool (by Mercury Interactive, now HP) to test the performance of an application and also determine how it would behave under stress. Load Runner consists of four main components. The Virtual User Generator, the Controller, an Agent and the Analyzer.
A figure illustrating all the parts of a load runner in action.
The Virtual User Generator (VuGen) is used to record/script the transactions or user actions that you want to stress. (eg Creating New User Account or Search feature in an online shopping application). Once recorder, the script can be modified to handle dynamic content (like user id of an account).
The Controller is the central control from where the entire test is created and monitored. This is where you create a scenario. A scenario is a collection of VuGen scripts that you want to run together in a test. Say you want to test a scenario where 100 concurrent users hit the application and create a new account. At the same time 50 users are using the search feature. Then 50 users get off the system and another 200 gets on and start using search. This goes on for a couple of hours and then suddenly 1000 users hit the system. You can create the above test using a controller and also monitor it in the real time.
A load runner agent is a light utility that resides on the application server ( or servers in case of a clustered environment with load balancing). The only job of this agent is to collect all the performance and network data on the servers (like perfmon counters, Virtual Memory usage, physical memory usage, paged pool memory, non-paged pool memory, thread count, handle count and stuff like that) and send it across to the controller. The frequency of this data collection and transfer can be preset. An agent is kept as light weight as possible to make sure that i does not adversely affect the server performance.
The controller also stores all the data collected from various sources into a database. The job of an Analyzer is to pull this data from the database and analyze it. Basically dig information out of the data.
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