2.7 Performance Checklist

• Use system- and network-level monitoring utilities to assist when measuring performance.

• Run tests on unloaded systems with the test running in the foreground.

  • Use System.currentTimeMillis( ) to get timestamps if you need to determine absolute times. Never use the timings obtained from a profiler as absolute times.

  • Account for performance effects of any caches.

• Get better profiling tools. The better your tools, the faster and more effective your tuning.

  • Pinpoint the bottlenecks in the application: with profilers, by instrumenting code (putting in explicit timing statements), and by analyzing the code.

  • Target the top five to ten methods, and choose the quickest to fix.

  • Speed up the bottleneck methods that can be fixed the quickest.

  • Improve the method directly when the method takes a significant percentage of time and is not called too often.

  • Reduce the number of times a method is called when the method takes a significant percentage of time and is also called frequently.

• Use an object-creation profiler together with garbage-collection statistics to determine which objects are created in large numbers and which large objects are created.

  • See if the garbage collector executes more often than you expect.

  • Determine the percentage of time spent in garbage collection and reduce that if over 15% (target 5% ideally).

  • Use the Runtime.totalMemory( ) and Runtime.freeMemory( ) methods to monitor gross memory usage.

• Check whether your communication layer has built-in tracing features.

  • Check whether your communication layer supports the addition of customized layers.

• Identify the number of incoming and outgoing transfers and the amounts of data transferred in distributed applications.