What's the default heap size for IBM's J9VM?

Question

I have IBM's J9 VM (build 2.3, J2RE 1.5.0 IBM J9 2.3) installed. After getting an OOM, the size of the heap dump is 383MB. How much heap does the JVM have?

The reason why I ask is that a 400MB heap dump seems a bit much for the default 64MB heap that I expect but I didn't specify any -Xm options. Does J9 use a different default heap size? If so, how can I find out what it is?

Answer 1

According to the documentation, the default minimum and maximum heap sizes are platform-dependent. On most platforms, default -Xms is 4M. Default -Xmx for Linux is "Half the real memory with a minimum of 16 MB and a maximum of 512 MB", and for Windows, it's "Half the real memory with a minimum of 16 MB and a maximum of 2 GB".

Answer 2

To print the current values, use:

java -verbose:sizes -version