Two important things in the Java performance engineer’s arsenal:


To capture a thread dump:

jstack -l <JAVA_PID>

To capture a heap dump file (to browse the heap dump, you can use jhat (Java Heap Analysis Tool)):

jmap -dump:format=b,file=heap.hprof JAVA_PID
# creates a file named heap.hprof


What’s causing high CPU?

To check what might be causing high CPU, capture a thread dump of the Java process in question, for example by using jstack at regular intervals, e.g. every 30 seconds. Then analyse the thread dump(s) using a tool like Thread Dump Analyzer.

Get information about threads

Use ps -eLF to get information about all threads, e.g. ps -eLF | grep <pid> | wc -l will count the number of threads for a PID.

What’s causing threads to be stuck in park()

park() causes a thread to be placed into a waiting state.