How to generate a thread dump in DSE DataStax

When high CPU is an issue, sometimes generating a thread dump is the only way to troubleshoot. You need to see which threads are consuming memory. You can do that with DSE through the nodetool sjk:

nodetool sjk stcap -p <jmx port> -o <output filename>.std -t 300s -i 1s

The above will produce a well compacted binary file. The -t is the timeout, and -i is the interval. The above parameters mean the dump will run for 300s and collect the threads every 1s.

You can then get a flamegraph of the above thread dumps using the same sjk:

nodetool sjk ssa -f <output filename>.std --histo

Or, if you simply want to view the threads, you can use the following:

nodetool sjk ssa -f <output filename>.std --print

If you want to use an external tool, I recommend https://fastthread.io/, then you’ll need the dump in human readable format. The above can be saved to file:

nodetool sjk ssa -f <output filename>.std --print > my-threads.out

And then used in any tool.