I have a production server running with the following flag: -XX:+HeapDumpOnOutOfMemoryError
Last night it generated a java-38942.hprof file when our server encountered a heap error. It turns out that the developers of the system knew of the flag but no way to get any useful information from it.
I suspect we have a major memory leak in our ActiveMQ connection bridge - we're seeing typical memory leak patterns (app loads fine, slows down if it runs for prolonged periods of time or is restarted over and over again over short periods of time). I looked up modern best practices for finding Java memory leaks and a lot of developers seem to be abandoning traditional tools like jhat/jmap in lieu of the new(er)jvisualvm.
Upon launching this tool (and spending a few hours reading over its tutorial) I am able to take profiler snapshots for both CPU and memory.
I'm just sort of stuck at this point - how do I analyze these snapshots to identify the leak? There's a plethora of documentation out there as to how to use jvisualvm to produce snapshots, but very little documentation as to how to actually make sense of them.
Analysing memory leak using visualvm is not that easy. It has a tool/plugin called 'sampler'. This can be used to sample memory or cpu. You can take snapshot at regular interval and look for possible leaks. Here is some details on how to use it- Obtained from quick search
More effective way will be to get a heap dump (say when the application has slowed down or when OOM happens). VisualVM help you to take heapdump (using Heap Dump on Monitor tab)