Java Garbage Collection Tuning

J2SE 1.4.1 and later versions offer several options in order to tune the garbage collection of Java Virtual Machine (JVM) even for multiprocessing environments. The intention is to minimize pauses (delay) and/or maximize throughput. It depends on the requirements of your application which of the JVM garbage collection settings would be of help. However there are some general rules of thumb for choosing the best matching algorithm.

	Default Collectors	Low Pause Collectors		Throughput Collectors	Heap Sizes
Generation		1 CPU	2+ CPUs	2+ CPUs and 1GB+ Heapsize
Young	Copying Collector default	Incremental Train Collector `-Xincgc` (causes appx. 10% slower overall GC)	Parallel Copying Collector `-XX:+UseParNewGC`	Parallel Scavenge Collector `-XX:+UseParallelGC -XX:+UseAdaptiveSizePolicy` or `-XX:+AggressiveHeap`	`-XX:NewSize, -XX:NewRatio, -XX:SurvivorRatio or -Xmn (fixed size)`
Old	Mark-Compact Collector default		Concurrent Collector `-XX:+UseConcMarkSweepGC`	Mark-Compact Collector default	`-Xms, -Xmx`
Permanent	Can be turned off with `-Xnoclassgc`. Use with care!				`-XX:PermSize, -XX:MaxPermSize`

Web Resources

Performance Documentation for the Java HotSpot VM

How does garbage collection work?

Generational and concurrent garbage collection

Turbo-charging Java HotSpot Virtual Machine, v1.4.x to Improve the Performance and Scalability of Application Servers

Improving Java Application Performance and Scalability by Reducing Garbage Collection Times and Sizing Memory Using JDK 1.4.1