How can I see which garbage collector java is using

Question

The Java Virtual Machine supports several garbage collection strategies.

This article explains them.

Now I am wondering which (automatically selected) strategy my application is using, is there any way to let the JVM(version 1.6) print this information?

Edit: The JVM detects if it is in client or server mode. So the question really is how can I see which has been detected?

Answer 1

jmap -heap

Prints a heap summary. GC algorithm used, heap configuration and generation wise heap usage are printed.

http://java.sun.com/javase/6/docs/technotes/tools/share/jmap.html

Answer 2

http://java.sun.com/j2se/1.5.0/docs/guide/vm/gc-ergonomics.html which is applicable for J2SE 6 as well states that the default is the Parallel Collector.

We tested this once on a JVM 1.5 by setting only

-server -Xms3g -Xmx3g -XX:PermSize=128m -XX:LargePageSizeInBytes=4m -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps

and the output showed

41359.597: [GC [PSYoungGen: 90499K->32K(377344K)] 268466K->181862K(2474496K), 0.0183138 secs]
41359.615: [Full GC [PSYoungGen: 32K->0K(377344K)] [PSOldGen: 181830K->129760K(2097152K)] 181862K->129760K(2474496K) [PSPermGen: 115335K->115335K(131072K)], 4.4590942 secs]

where PS stands for Parallel Scavenging