How to Determine the Metaspace Size at Runtime in Java 8

How can I find out the size of Metaspace during runtime in a Java 8 application?

System.out.println("Current Metaspace Size: " + ManagementFactory.getMemoryMXBean().getNonHeapMemoryUsage().getUsed() + " bytes");

In Java 8, Metaspace replaces the permanent generation and is used to store class metadata. Monitoring the size of Metaspace is crucial for understanding memory usage and optimizing performance. In this guide, we will explore how to find out the Metaspace size at runtime using the Java Management API.

import java.lang.management.ManagementFactory;
import java.lang.management.MemoryMXBean;

public class MetaspaceChecker {
    public static void main(String[] args) {
        MemoryMXBean memoryMXBean = ManagementFactory.getMemoryMXBean();
        long metaspaceSize = memoryMXBean.getNonHeapMemoryUsage().getUsed();
        System.out.println("Current Metaspace Size: " + metaspaceSize + " bytes");
    }
}

Causes

• Understanding Metaspace and its role in Java memory management.
• Importance of tracking Metaspace size in identifying memory leaks and optimizing application performance.

Solutions

• Use the ManagementFactory and MemoryMXBean classes to retrieve Metaspace memory usage details.
• To monitor Metaspace usage programmatically, use the method shown in the code snippet below.

Mistake: Not including necessary imports when using ManagementFactory.

Solution: Ensure to import `java.lang.management.ManagementFactory` and related classes.

Mistake: Misunderstanding memory usage semantics (Heap vs. Non-Heap).

Solution: Remember that Metaspace is part of the Non-Heap memory.