finding out memory allocation hotspots in java

Question

Our GC is working hard and we have some pauses that we want to decrease. We have some memory allocation issues that we want to solve before or while we are tweaking with the actual JVM GC args.

I would like to know which objects are making the GC sweat:

1. is there a way to know which objects are evacuated every time the GC is working?
2. is there a way to know which objects are moved between areas every time the GC is working?
3. Is there a way to know which objects are in Eden area?

I am working extensively with Jprofiler and Memory Analyzer. I would like to get this information on a running application in my staging environment.

Answer 1

For 2 and 3, you can use the -XX:+PrintGCDetails and -XX:+PrintGCTimeStamps flags with either Oracle or OpenJDK java executable during a run session of your application

Answer 2

For question 1, Phantom References can be used. This will allow you to be notified when an object is GC'ed (or GC-able).

As to the other two, I don't quite know.