General strategy to resolve Java memory leak?

Question

I have a standalone program that I run locally, it is meant to be a server type program running 24/7. Recently I found that it has a memory leak, right now our only solution is to restart it every 4 hours. What is the best way to go about finding this memory leak? Which tool and method should we use?

Answer 1

As already stated jvisualvm is a great way to get started, but once you know what is leaking you may need to find what is holding references to the objects in question for which I'd recommend jmap and jhat, e.g

jmap -dump:live,file=heap.dump.out,format=b <pid>

and

jhat heap.dump.out

where <pid> is easily found from jvisualvm. Then in a browser navigate to localhost:7000 and begin exploring.

Answer 2

One approach would be to take heap dumps on a regular basis, then trend the instance counts of your classes to try to work out which objects are being consistently created but not collected.

Another would be to switch off parts of your app to try to narrow down where the problem is.

Look at tools like jmap and jhat.

Answer 3

When it comes to hunting memory problems, I use SAP Memory Analyzer Eclipse Memory Analyser (MAT), a Heap Dump analysis tool.

The Memory Analyzer provides a general purpose toolkit to analyze Java heap dumps. Besides heap walking and fast calculation of retained sizes, the Eclipse tool reports leak suspects and memory consumption anti-patterns. The main area of application are Out Of Memory Errors and high memory consumption.

Initiated by SAP, the project has since been open sourced and is now know as Eclipse Memory Analyser. Check out the Getting Started page and especially the Finding Memory Leaks section (I'm pasting it below because I fixed some links):

Start by running the leak report to automatically check for memory leaks.

This blog details How to Find a Leaking Workbench Window.

The Memory Analyzer grew up at SAP. Back then, Krum blogged about Finding Memory Leaks with SAP Memory Analyzer. The content is still relevant!

This is probably the best tool you can get (even for money) for heap dump analysis (and memory leaks).

PS: I do not work for SAP/IBM/Eclipse, I'm just a very happy MAT user with positive feedback.

Answer 4

You might look up JMX and the jconsole app that ships with Java. You can get some interesting statistics out-of-the-box, and adding some simple instrumentation to your classes can provide a whole lot more.

Answer 5

You need a memory profiler. I recommend trying the Netbeans profiler.

Answer 6

If you are using Java from Sun and you use at least Java 6 update 10 (i.e. the newest), then try running jvisualvm from the JDK on the same machine as your program is running, and attach to it and enable profiling.

This is most likely the simplest way to get started.