Investigate debugging tools for OpenJ9

[adleong]

Linkerd can be run on the OpenJ9 JVM. What tools are available for debugging issues when running on OpenJ9?

Does OpenJ9 export metrics or diagnostic data?
What existing JDK tools work with OpenJ9? jmap? jconsole? Can you attach a java debugger to it? How do you profile it? Java flight recorder?
How do you get a heap dump? How do you analyze it?
How do you monitor and debug GC issues? Does it emit gc logs in the same format?

[adleong]

starting point: https://www.ibm.com/support/knowledgecenter/SSYKE2_8.0.0/com.ibm.java.vm.80.doc/docs/diag_tools_intro.html

[adleong]

Adding the -Xdump:heap:events=user command line option allows a heapdump and javacore files to be created when a SIGQUIT signal is sent to the JVM. This can be triggered by running kill -3 1.

The javacore contains detailed information about the current state of the JVM including a thread dump. It can be analyzed with JCA: https://www.ibm.com/developerworks/community/groups/service/html/communitystart?communityUuid=2245aa39-fa5c-4475-b891-14c205f7333c

The heapdump is in PHD format and cannot be analyzed by Hotspot heap analyzer tools. Instead, it can be inspected using HA: https://www.ibm.com/developerworks/community/groups/service/html/communitystart?communityUuid=4544bafe-c7a2-455f-9d43-eb866ea60091

[adleong]

Eclipse MAT can be made to understand PHD heap dumps by adding the DTFJ plugin:

1. In MAT, go to help -> Install new software
2. Add a site: http://public.dhe.ibm.com/ibmdl/export/pub/software/websphere/runtimes/tools/dtfj/
3. Select "Diagnostic Tool Framework for Java" and install it