Inside the JVM - Profiling & Diagnosing Memory Leaks in Java

A few months back, while working on a backend service that used Drools for rule evaluation, I noticed something odd - JVM heap usage kept climbing, GC metrics were off, and eventually, the service crashed with an OutOfMemoryError. Profiling the JVM with VisualVM and Java Flight Recorder, and analyzing a heap dump revealed a memory leak tied to rule engine objects.

The root cause? A Drool’s Session resource that wasn’t closed properly. That one oversight let to retained references, bloated heap and a production outage.