This is one of the things I've always liked about JRuby. You can use the excellent tooling of the JVM ecosystem (e.g. YourKit, Coverity Dynamic Analyzer) to understand the behavior of your JRuby applications, and even attach directly to running production apps to debug them.

I've found tools like this essential for debugging multithreaded JRuby applications, and there's simply nothing else like them available for MRI.