[kjkoster]

Dear All,

The HotSpot JVM has a very useful command line flag: –XX:+HeapDumpOnOutOfMemoryError. As the name suggests, this flag makes Java automatically dump its heap memory on an OutOfMemoryError.

This flag is great for systems that bomb out when you are sleeping. In the morning you'll not only find the exception in the logs, but also an nice, fat heap dump to throw your analysis tools at.

This flag may not be so great to use when you run your JVM with a very large heap. Dumping a help that is more than a few GB may take quite some time.

Kees Jan

[Barry]

We have a process that goes boom once in a blue moon with a total heap of about 5GB

Fortunately the latest Netbeans Milestones for 6.7 include query functionality for the heapwalker:
"OQL support for heapwalker
Now it is possible to use jHat compatible OQL queries to analyze the contents of the heapdump. The OQL support offers a basic syntax and keyword highlighting, code completion for OQL keywords and the class names on the heap and the query results are integrated with the rest of the heapwalker. "

[kjkoster]

Dear Barry,

How well does Netbeans cope with dumps of 5GB heaps? How much RAM do you need in your machine to be able to analyse such a heap dump?

Kees Jan

[Barry]

That's what I'm hoping to find out next time ;-)