How do I analyze a .hprof file?

Question

I have a production server running with the following flag: -XX:+HeapDumpOnOutOfMemoryError

Last night it generated a java-38942.hprof file when our server encountered a heap error. It turns out that the developers of the system knew of the flag but no way to get any useful information from it.

Any ideas?

Answer 1

You can use HAT, The Java Heap Analysis Tool

Answer 2

If you want a fairly advanced tool to do some serious poking around, look at the Memory Analyzer project at Eclipse, contributed to them by SAP.

Some of what you can do is mind-blowingly good for finding memory leaks etc -- including running a form of limited SQL (OQL) against the in-memory objects, i.e.

SELECT toString(firstName) FROM com.yourcompany.somepackage.User

Totally brilliant.

Answer 3

Just get the Eclipse Memory Analyzer. There's nothing better out there and it's free.

JHAT is only usable for "toy applications"

Answer 4

You can also use HeapWalker from the Netbeans Profiler or the Visual VM stand-alone tool. Visual VM is a good alternative to HAT as it is stand alone, but is much easier to use than HAT.

You need Java 6+ to fully use Visual VM.