Java Performance Tuning

Performance Checklist

Many of these suggestions apply only after a bottleneck has been identified:

• Test your benchmarks on each version of Java available to you (classes, compiler, and VM) to identify any performance improvements.

  • Test performance using the target VM or “best practice” VMs.

  • Include some tests of the garbage collector appropriate to your application, so that you can identify changes that minimize the cost of garbage collection in your application.

  • Run your application with both the -verbosegc option and with full application tracing turned on to see when the garbage collector kicks in and what it is doing.

  • Vary the -Xmx/-Xms option values to determine the optimal memory sizes for your application.

  • Avoid using the VM options that are detrimental to performance.

• Replace generic classes with more specific implementations dedicated to the data type being manipulated, e.g., implement a LongVector to hold longs rather than use a Vector object with Long wrappers.

  • Extend collection classes to access internal arrays for queries on the class.

  • Replace collection objects with arrays where the collection object is a bottleneck.

• Try various compilers. Look for compilers targeted at optimizing performance: these provide the cheapest significant speedup general to all runtime environments.

  • Use the -O option (but always check that it does not produce slower code).

  • Identify the optimizations a compiler is capable of so that you do not negate the optimizations.

  • Use a decompiler to determine ...