HotSpot VM Adaptive Tuning

The Java 5 HotSpot VMs introduced a new feature that evaluates the underlying platform and system configuration at JVM launch time and then automatically selects the garbage collector, configures Java heap size, and chooses a runtime JIT compiler to use. In addition, this feature also introduced an adaptive means for tuning the Java heap for the throughput garbage collector. This new adaptive Java heap tuning allowed the garbage collector to dynamically tune the sizes of the Java heap to meet application behavior and object allocation rates. This combination of automatic platform dependent selection of default values and adaptive Java heap sizing to lessen the burden of manual garbage collection tuning is called ergonomics.

The ergonomics feature has been further enhanced in Java 6 Update 18 to improve the performance of rich client applications. In this section, the initial default values for heap sizes, garbage collector, and JIT compilers found in Java 1.4.2 HotSpot VMs are presented, followed by the default values chosen via the ergonomics feature and the Java 6 Update 18 ergonomics enhancements.