Java/Tomcat heap size question

I am not a Java dev, but开发者_开发技巧 an app landed on my desk. It's a web-service server-side app that runs in a Tomcat container. The users hit it up from a client application.

The users constantly complain about how slow it is and the app has to be restarted about twice a week, cause things get really bad.

The previous developer told me that the app simply runs out of memory (as it loads more data over time) and eventually spends all its time doing garbage collection. Meanwhile, the Heap Size for Tomcat is set at 6GB. The box itself has 32GB of RAM.

Is there any harm in increasing the Heap Size to 16GB?

Seems like an easy way to fix the issue, but I am no Java expert.

You should identify the leak and fix it, not add more heap space. Thats just a stop gap.

You should configure tomcat to dump the heap on error, then analyze the heap in one of any number of tools after a crash. You can compute the retained sizes of all the clases, which should give you a very clear picture of what is wrong.

Im my profile I have a link to a blog post about this, since I had to do it recently.

No, there is no harm in increasing the Heap Size to 16GB.

The previous developer told me that the app simply runs out of memory (as it loads more data over time)

This looks like a memory leak, a serious bug in application. If you increase the amount of memory available from 6 to 16 GiB, you're still gonna have to restart the application, only less frequent. Some experienced developer should take a look at the application heap while running (look at hvgotcodes tips) and fix the application.

To resolve these issues you need to do performance testing. This includes both CPU and memory analysis. The JDK (6) bundles a tool called VisualVM, on my Mac OS X machine this is on the path by default as "jvisualvm". That's free and bundled, so it's a place to start.

Next up is the NetBeans Profiler (netbeans.org). That does more memory and CPU analysis. It's free as well, but a bit more complicated.

If you can spend the money, I highly recommend YourKit (http://www.yourkit.com/). It's not terribly expensive but it has a lot of built-in diagnostics that make it easier to figure out what's going on.

The one thing you can't do is assume that just adding more memory will fix the problem. If it's a leak, adding more memory may just make it run really badly a bit longer between restarts.

I suggest you use a profiling tool like JProfiler, VisualVM, jConsole, YourKit etc. You can take a heap dump of your application and analyze which objects are eating up memory.