IBM J9 Diagnostics

Here at $DAYJOB we're using the IBM J9 JVM for our test and production deployments. I've had some performance and memory problems recently, so here's a quick entry about some of the things the J9 JVM provides for diagnotics.

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...text
  
• 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