Java Performance, 2nd Edition

Chapter 5. An Introduction to Garbage Collection

This chapter covers the basics of garbage collection within the JVM. Short of rewriting code, tuning the garbage collector is the most important thing that can be done to improve the performance of a Java application.

Because the performance of Java applications depends heavily on garbage collection technology, it is not surprising that quite a few collectors are available. The OpenJDK has three collectors suitable for production, another that is deprecated in JDK 11 but still quite popular in JDK 8, and some experimental collectors that will (ideally) be production-ready in future releases. Other Java implementations such as Open J9 or the Azul JVM have their own collectors.

The performance characteristics of all these collectors are quite different; we will focus only on those that come with OpenJDK. Each is covered in depth in the next chapter. However, they share basic concepts, so this chapter provides a basic overview of how the collectors operate.

Garbage Collection Overview

One of the most attractive features of programming in Java is that developers needn’t explicitly manage the life cycle of objects: objects are created when needed, and when the object is no longer in use, the JVM automatically frees the object. If, like me, you spend a lot of time optimizing the memory use of Java programs, this whole scheme might seem like a weakness instead of a feature (and the amount of time I’ll spend covering GC might seem to lend ...