is the environment variable IBM_HEAPDUMP enabled by default in IBM J9 JVM?

Question

i wonder if the environment variable IBM_HEAPDUMP enabled by default in IBM J9? I searched through the internet and somebody say it is while other say not. Let me suppose if it's active by default, that means, the signal-based heapdump has been enabled. And JVM would catch all the pre-defined signal and generate heapdump accordingly. However, if so like above, why do we still need to configure with -Xdump:what? just as link described http://www-304.ibm.com/support/docview.wss?uid=swg21246238. The another question is whether IBM_HEAPDUMP and -Xdump:what are functioning overlap here? Or i'm totally understanding wrongly with these two.

Thanks in advance

Answer 1

You're misunderstanding :-)

-Xdump:what doesn't configure anything. It simply shows what dumps are enabled on the JVM in question. Thus you can look at the output from -Xdump:what to see what's enabled. By default, yes, there's dumps enabled like IBM_HEAPDUMP but you may want more control/detail.