What is a Heap dump ?
A heap dump is a snapshot of the memory of a Java process at a certain point of time. The snapshot contains information about the java objects and classes in the heap at the moment the snapshot was triggered.
What is a Thread dump dump ?
A thread dump is a snapshot of the state of all threads that are part of the process. The state of each thread is presented in a stack trace, which shows the contents of a thread’s stack. This is especially useful if application seems stuck, or is running out of resources, a thread dump will reveal the state of the server.
How to create heap dump and thread dump
Once the AdminServer has started up, to get heap dump and/or thread dump take a snapshots with both j
map to see what changed and with
jstack if something is blocked.
Step 1: Find the PID of the java process
- Java JDK ships with the jps command which lists all java process ids running on the machine including the PID of the process.
- <DLC>\jdk\bin\jps -l -m -v
- Example, the adminserver is running on PID 912
912 com.progress.chimera.adminserver.AdminServerStarter -port 20946 -adminport 7846 ...
Step 2: Request a Thread Dump from the JVM
- The jstack tool prints thread dumps to the command line console or a file,
- The thread dumps can be used to see which threads are blocked
- The -l argument provides additional "Locked ownable synchronizers" for each thread
- To obtain a thread dump using jstack, use the PID of the AdminServer java process (912) to run the following command at least 5 times over a few seconds interval, changing the output filename:
<DLC>\jdk\bin\jstack -l 912 >> admserv.jstak_912_1
Step 3: Request a Heap Dump from the JVM
- The jmap tool it prints out what is in the memory to see what changed to the command line console or a file.
- To obtain a heap dump using jmap, use the PID of the AdminServer java process (912) to run the following commands :
a. With -heap to see the java heap summary:
<DLC>\jdk\bin\jmap -heap 912 >> admserv.jmap912_1
b.With -dump to dump the full java heap:
<DLC>\jdk\bin\jmap -dump:file=admserv912_1.dump 912
On AIXThe methods are different for IBM Java.
Find the PID of the AdminServer java process:
$ ps -ef | grep java | grep AdminServer
kill -3 <AdminServerPID>
A file will be created with the format: javacore.<date>.<time>.<PID>
When a full heap dump is needed:1 - Identify the AdminServer PID
ps -ef | grep Java | grep adminServer
or follow this article from IBM
https://www.ibm.com/support/pages/finding-which-program-using-port-aix2 - Generate a core file
gencore <pid> <output filePath>
3- Generate a ZIP file from the dump:
$JAVA_HOME/jre/bin/jextract <coreFilePath>
