IBM WebSphere Application Server Performance Cookbook

General Performance Recipes

  1. Performance tuning is usually about focusing on a few key variables. The recipes will highlight the most common variables that often improve the speed of the average application by 100% or more relative to the default configuration. Additional tuning should be guided by evidence using the scientific method. Gather data, analyze it and create hypotheses. Then test and evaluate your hypotheses. Repeat.
  2. There is a seemingly daunting number of tuning knobs. We try to document everything in detail in case you hit a problem in that area; however, unless you are trying to squeeze out every last drop of performance, we do not recommend a close study of every point.
  3. In general, we advocate a bottom-up and integrated approach. Bottom-up means, for example, start with the operating system, then Java, then WebSphere, then the application, etc. Integrated means gather data on all layers at the same time, if possible.
  4. One of the most difficult aspects of performance tuning is understanding whether or not the architecture of the system, or even the test itself, is valid and/or optimal.
  5. Meticulously describe and track the investigation, each test and its results.
  6. Use statistics (minimums, maximums, averages, medians, and standard deviations) instead of spot observations.
  7. When benchmarking, use a repeatable test that accurately models production behavior, and avoid short term benchmarks which may not have time to warm up.
  8. To investigate bottlenecks, consider the key variables including request arrivals, concurrent threads, and response times.
  9. Take the time to automate as much as possible: not just the testing itself, but also data gathering and analysis. This will help you iterate and test more hypotheses.
  10. Make sure you are using the latest version of every component because there are often performance or tooling improvements available.
  11. When researching issues, you can either analyze or isolate them. Analyzing means taking particular symptoms and generating hypotheses on how to change those symptoms. Isolating means finding an issue through the process of elimination. In general, we have found through experience that analysis is preferable to isolation.
  12. Review the full end-to-end architecture. Certain internal or external products, devices, content delivery networks, etc. may artificially limit performance (e.g. Denial of Service protection), periodically mark services down (e.g. network load balancers, WAS plugin, etc.), or become bottlenecks themselves (e.g. CPU on load balancers, etc.).

For details, see the General chapter.