James's Blog

Java: GC tunning

http://www.petefreitag.com/articles/gctuning/

3.2 The Young Generation
The bigger the young generation the less minor GC's, but this implies a smaller tenured generation which increases the frequency of major collections.
You need to look at your application and determine how long your objects live for to tune this.
-XX:NewRatio=3 - the young generation will occupy 1/4 the overall heap
-XX:NewSize - Size of the young generation at JVM init. Calculated automatically if you specify -XX:NewRatio
-XX:MaxNewSize - The largest size the young generation can grow to (unlimited if this value is not specified at command line)

4 Types of Collectors
Everything to this point talks about the default garbage collector, there are other GC's you can use
Throughput Collector - Uses a parallel version of the young generation collector
-XX:+UseParallelGC
Tenured collector is the same as in default
Concurrent Low Pause Collector
Collects tenured collection concurrently with the execution of the app.
The app is paused for short periods during collection
-XX:+UseConcMarkSweepGC
To enable a parallel young generation GC with the concurrent GC add -XX:+UseParNewGC to the startup. Don't add -XX:+UseParallelGC with this option.
Incremental Low Pause Collector
Sometimes called Train Collector
Collects a portion of the tenured generation at each minor collection.
Tries to minimize large pause of major collections
Slower than the default collector when considering overall throughput
Good for client apps (my observation)
-Xincgc
Don't mix these options, JVM may not behave as expected.

posted by James Pei @ 10:53 AM