Heap Dump

DSE Version: 6.0

Video

If something goes wrong with your Apache Cassandra nodes and they run out of memory, you may need to dive deep to understand what exactly is happening. In this case, you may want to use the heap dump tool. Learn more about heap dump in this unit.

Transcript: 

If something goes seriously askew with your Apache Cassandra nodes and they run out of memory, you may need to dive deep to understand what is happening. In this case you may want to take a look at Heap Dump. Heap dump is a tool that shows you the contents of your heap when the Apache Cassandra process dies. To be able to review a heap dump after a Java process dies, you need to start the process with the “plus-heap-dump-on-out-of-memory-error option enabled - as shown on the slide (which is the default).

If you are seeing errors like this in your log file, you may be approaching an “out of memory” event - in which case, a heap dump will help you understand why.

Java stores the heap dump in a file, but you need to make sure that the Apache Cassandra process has write access to the directory BEFORE the process tries to create the heap dump. You also need to make sure there is enough space on the disk to hold the heap dump. The default location is in a subdirectory off the root where the process runs.

Eclipse has a Memory Analyzing Tool that helps you understand the heap dump file. We won’t go into how to use this tool in this course, but there are lots of Youtube tutorials to help you with that. Chances are you will never need to analyze a heap dump, but in the off-chance that you ever want to, be aware that there is an Eclipse tool to help you out.

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