Garbage Collection (GC) liberates the programmer from having to call malloc and free. More importantly GC saves the programmer from having to debug their mistakes when using malloc and free. Unfortunately the details of how GC works are often a black box. This talk will start with a tour of all of the GC algorithms currently available in OpenJDK. We'll discuss how they work, their strengths and weaknesses, and which class of applications they were developed for. We'll work our way through serial gc, parallel gc, concurrent mark and sweep, and g1. We'll make the case for why we need all of them and just one more GC algorithm, Shenandoah.

Shenandoah is a parallel and concurrent GC algorithm designed for applications with 100gb+ heaps and tight pause time constraints. It's the first GC algorithm targeting OpenJDK which compacts the live objects while the Java threads are running. We'll describe the algorithm itself, the implementation details, and the optimizations needed to achieve good performance. We'll present performance numbers and give a demo that visualizes Shenandoah.