Bitten by the OOME

It's been a slow blogging week as I've been pre-occupied chasing a Java OutOfMemoryError (OOME). OOME is one of the most dreaded problems in the Java world. Not easy fix other than hooking up a profiler and debugging your way through it. I was impressed by JMP as a Free/OSS tool (No, I'm not using Eclipse so the plugins are of no use to me) specially on win32 systems, however you need a fair bit of memory (+512mb) for a large app. I'd also recommend YourKit on the commercial front.

The problem turned out to be too many String temporaries caused by excessive logging in our app (I didn't discover it...doh!!!). Increasing the JVMs "MaxPermSize" also had a dramatic effect on Garbage Collection.

Some useful links I came across are

• Java GC is discussed in detail here, here and here (+Performance Portal).
• 1.5 now provides a nice Platform Monitoring and Management API allowing apps to monitor the JVM act on events. For example it's possible to monitor the heap and clear caches when memory thresholds are reached. (No good for me as we use 1.4.2). Here is a nice example.
• A comprehensive list of JVM options.
• Some performance tips for developers.