Java: non-heap-memory analyzes

Question

we have the problem that our non-heap-memory is growing all the time. so we have to restart our jee (java8) - webapp every 3rd day (as you can see in the screenshot here: sc

Answer 1

Non-heap memory usage, as provided by MemoryPoolMXBean counts the following memory pools:

• Metaspace
• Compressed Class Space
• Code Cache

In other words, standard non-heap memory statistics includes spaces occupied by compiled methods and loaded classes. Most likely, the increasing non-heap memory usage indicates a class loader leak.

Use

• jmap -clstats PID to dump class loader statistics;
• jcmd PID GC.class_stats to print the detailed information about memory usage of each loaded class. The latter requires -XX:+UnlockDiagnosticVMOptions.

Answer 2

With Java 8, class meta data is now in a non-heap memory section called Metaspace (and not in PermGen anymore). If your non-heap memory is mainly consumed by Metaspace, you can figure it out with jstat.

It's not a general tool for analyzing non-heap memory. But it might still help in your case.

Answer 3

As @apangin points out it looks like you are using more Metaspace over time. This is usually means you are loading more classes. I would record which classes are being loaded and methods being compiled and try to limit how much this is being done in production on a continuous basis. It is possible you have a library which is generating code continuously but not cleaning it up. This is where looking at what classes are being created could give you a hint as to which one.

---

For native non-heap memory.

You can look at the memory mapping on Linux with /proc/{pid}/maps This will let you know how much virtual memory is being used.

You need to determine whether this is due to

• increasing numbers of threads, or sockets
• direct ByteBuffers being used.
• a third party library which is using native / direct memory.

From looking at your graphs you could reduce your heap and increase your maximum direct memory and extend the restart time to a week or more, but a better solution would be solve the cause.