First up: the diagnostics documentation summary.
Next, here's a series of things you can get the J9 JVM to give you:
- GC log - use the standard -verbose:gc command line option to get an XML file dump of garbage collection activity. You can set the output directory,
- Heapdump log - generated when you call it explicitly in your app, or more likely, automatically when you have an OutOfMemory condition. *.phd files are created which are not human-readable
- Javadump log (a/k/a javacore or thread dump) - contains human-readable data on the the operating system, the application environment, threads, stacks, locks, and memory. Creates files starting with javacore.
- System dump (a/k/a core dump) - typically only produced when the jvm fails unexpectedly. Log contains active processes, threads, and system memory. Creates files named Snap*.trc