Java Profiler

HProf is a simple CPU Heap profiling tool. Hadoop's profiling also uses it. Here is the link.

JVM Garbage Collector (Tuning)

java.lang.OutOfMemoryError: GC overhead limit exceeded means garbage collector is taking so much ( > 98% ) time and can't open up as much space in memory ( < 2% ). I got this exception while working on a large dataset and holding ~1G of data in memory. One way to get over this exception is using a specific jvm garbage collector called Concurrent Collector. Concurrent collector does not let executing program to pause for a long time because of gc. Also concurrent collector takes advantage of multiple CPUs available in the environment. Can be enabled via -XX:+UseConcMarkSweepGC

Tip: For RMI apps - unnecessary rmi garbage collection can be avoided via tuning its execution frequency. by default it runs every 60,000 msec.

-Dsun.rmi.dgc.client.gcInteraval=3600000
-Dsun.rmi.dgc.server.gcInteraval=3600000

References
- offial reference: [1]
- nice summary:  [2]