Swapping Code, Losing Memory: A JVM Deep Dive

You’ve probably seen the option to hot swap code while debugging in your IDE, but have you ever wondered how it actually works under the hood? And more importantly, what could go wrong? While stress testing an application that made heavy use of class reloading, I discovered a surprising issue: we were leaking memory and not just heap memory. This kicked off a deep dive into the internals of the JVM to understand what really happens when a class is reloaded. In this talk, I’ll explain how I investigated the problem, what I learned about class representation in the JVM, and how code hot swapping really works in OpenJDK. You’ll leave with practical insights into debugging class reloading issues and a better understanding of what’s happening behind the scenes when your code changes on the fly.