Found a great article on performance testing on Sys-con. The intro is below:

"Performance testing a J2EE application can be a daunting and seemingly confusing task if you don't approach it with the proper plan in place. As with any software development process, you must gather requirements, understand the business needs, and lay out a formal schedule well in advance of the actual testing.

The requirements for the performance testing should be driven by the needs of the business and should be explained with a set of use cases. These can be based on historical data (say, what the load pattern was on the server for a week) or on approximations based on anticipated usage. Once you have an understanding of what you need to test, you need to look at how you want to test your application.

Early on in the development cycle, benchmark tests should be used to determine if any performance regressions are in the application. Benchmark tests are great for gathering repeatable results in a relatively short period of time. The best way to benchmark is to change one and only one parameter between tests. For example, if you want to see if increasing the JVM memory has any impact on the performance of your application, increment the JVM memory in stages (for example, going from 1024 MB to 1224 MB, then to 1524 MB, and finally to 2024 MB) and stop at each stage to gather the results and environment data, record this information, and then move on to the next test. This way you'll have a clear trail to follow when you are analyzing the results of the tests. In the next section I'll discuss what a benchmark test looks like and the best parameters for running these tests.

Later on in the development cycle, after the bugs have been worked out of the application and it has reached a stable point, you can run more complex types of tests to determine how the system will perform under different load patterns. These types of tests are called capacity planning, soak tests, and peak-rest tests, and are designed to test "real-world"-type scenarios by testing the reliability, robustness, and scalability of the application."

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