Generating and Analyzing Heap Dumps

Problem

When to Take Heap Dumps

Heap dumps can be very useful when troubleshooting high memory utilization or OutOfMemoryErrors since they show exactly which objects are consuming most of the heap.

Automatic Heap Dumps

Apache Cassandra is configured to trigger a heap dump at the occurrence of an OutOfMemoryError, but unless you have set your CASSANDRA_HEAPDUMP_DIR in cassandra-env.sh, the file will be written in the Apache Cassandra process's working directory, or may not be written at all due to permission and/or space issues.

You can use the following where Apache Cassandra is running to check the path:

ps -ef | grep HeapDumpPath

Manual Heap Dumps

Live Objects Only

jmap -dump:live,format=b,file=/path/to/heapdump.hprof <pid>

jcmd <pid> GC.heap_dump /path/to/heapdump.hprof

nodetool sjk mx -mc -b "com.sun.management:type=HotSpotDiagnostic" -op dumpHeap -a "/path/to/heapdump.hprof" true

All Objects

jmap -dump:format=b,file=/path/to/heapdump.hprof <pid>

jcmd <pid> GC.heap_dump /path/to/heapdump.hprof -all

nodetool sjk mx -mc -b "com.sun.management:type=HotSpotDiagnostic" -op dumpHeap -a "/path/to/heapdump.hprof" false

Analyzing Heap Dumps

The recommended tool for analyzing heap dumps is Eclipse Memory Analyzer, available here: http://www.eclipse.org/mat/downloads.php. It is available as a stand-alone application or as a plugin for Eclipse. Analyzing a large heap dump will require a lot of memory, and you will probably also need to increase the Xmx in MemoryAnalyzer.ini. For a large heap dump, the initial analysis phase can take a long time. After it finishes analyzing the heap dump, you can view the dominator tree to see which objects retain the most heap.

If you need help troubleshooting a memory-related issue, please open a support case.