JVM performance tuning for large applications

Question

The default JVM parameters are not optimal for running large applications. Any insights from people who have tuned it on a real application would be helpful. We are running the

Answer 1

Look here (or do a google search for hotspot tuning) http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html

You definitely want to profile your app before you try to tune the vm. NetBeans has a nice profiler built into it that will let you see all sorts of things.

I once had someone tell me that the GC was broken for their app - I looked at the code and found that they never closed any of their database query results so they were retaining massive amounts of byte arrays. Once we closed the results the time went from over 20 mins and a GB of memory to about 2 mins and a very small amount of memory. They were able to remove the JVM tuning parameters and things were happy.