Book Image

Java Memory Management

By : Maaike van Putten, Dr. Seán Kennedy
Book Image

Java Memory Management

By: Maaike van Putten, Dr. Seán Kennedy

Overview of this book

Understanding how Java organizes memory is important for every Java professional, but this particular topic is a common knowledge gap for many software professionals. Having in-depth knowledge of memory functioning and management is incredibly useful in writing and analyzing code, as well as debugging memory problems. In fact, it can be just the knowledge you need to level up your skills and career. In this book, you’ll start by working through the basics of Java memory. After that, you’ll dive into the different segments individually. You’ll explore the stack, the heap, and the Metaspace. Next, you’ll be ready to delve into JVM standard garbage collectors. The book will also show you how to tune, monitor and profile JVM memory management. Later chapters will guide you on how to avoid and spot memory leaks. By the end of this book, you’ll have understood how Java manages memory and how to customize it for the benefit of your applications.
Table of Contents (10 chapters)

Releasing Metaspace memory

One of the major changes from PermGen (pre-Java 8) to Metaspace (Java 8 onwards) is that the Metaspace can now grow in size. By default, the amount of memory allocated for the Metaspace is unbounded, as it is part of native memory. The size of the Metaspace can be customized using the JVM XX:MetaspaceSize flag.

The Metaspace can trigger garbage collection in only two scenarios:

  • Metaspace runs out of memory
  • Metaspace size exceeds a JVM-set threshold

Let us examine these in turn.

Metaspace runs out of memory

As stated, by default, the native memory available to the Metaspace is unlimited. If you run out of memory, you get an OutOfMemoryError message, and this will trigger a run of the garbage collector. You can limit the Metaspace size with the JVM –XX:MaxMetaspaceSize flag. If you reach this limit, that will also trigger a run of the garbage collector.

Metaspace size exceeds a JVM-set threshold

We can configure...