Chaos Engineering – Metaspace OutOfMemoryError

JVM memory has following regions: 

Fig: JVM memory regions

a. Young Generation

b. Old Generation

c. Metaspace

d. Others region


Video: To see the visual walk-through of this post, click below:


When you encounter ‘java.lang.OutOfMemoryError: Metaspace’ it indicates that the Metaspace region in the JVM memory is getting saturated. Metaspace is the region where metadata details that are required to execute your application are stored. In nutshell they contain Class definitions and method definitions of your application. To learn more about what gets stored in each of the JVM memory regions, you may refer to this video clip. In this post let’s discuss how one can simulate java.lang.OutOfMemoryError: Metaspace.

Simulating java.lang.OutOfMemoryError: Metaspace

To simulate ‘java.lang.OutOfMemoryError: Metaspace’, we wrote this program:

public class MetaspaceLeakProgram {
   
   public static void main(String[] args) throws Exception {
        
      ClassPool classPool = ClassPool.getDefault();

      while (true) {
            
         // Keep creating classes dynamically!
         String className = "com.buggyapp.MetaspaceObject" + UUID.randomUUID();
         classPool.makeClass(className).toClass();
      }
   }    
}

This program leverages the ‘ClassPool’ object from the opensource javassist library. This ‘ClassPool’ object is capable of creating new classes at runtime. Please take a close look at the above program. If you notice, this program keeps on creating new classes. Below is the sample class names generated by this program:

com.buggyapp.MetaspaceObject76a9a309-c9c6-4e5f-a302-8340eb3acdef
com.buggyapp.MetaspaceObjectb9bd6832-bacd-4c7c-a6e6-3bfa19a85e80
com.buggyapp.MetaspaceObject81d9d086-7245-4304-818f-0bfcbf319fd3
com.buggyapp.MetaspaceObjecte27068b6-f4cb-498a-80d5-0e5b61c2ada0
com.buggyapp.MetaspaceObject06f9d773-d365-48c8-a5cc-9c69b3178f4c
:
:
:

Whenever a new class is created, its corresponding class metadata definitions are created in the JVM’s Metaspace region. Since metadata definitions are created in Metaspace, it’s size starts to grow. When the maximum metaspace size is reached, application will experience ‘java.lang.OutOfMemoryError: Metaspace’

java.lang.OutOfMemoryError: Metaspace causes

 ‘java.lang.OutOfMemoryError: Metaspace’ error happens because of two reasons:

 a. Metaspace region size is under allocated 

 b. Memory leak in the Metaspace region. 

You can address #a by increasing Metaspace region size. You can do this by passing the JVM argument ‘-XX:MaxMetaspaceSize’. 

In order to address #b, you have to do proper troubleshooting. Here is a post which walks through how to troubleshoot memory leaks in the Metaspace region.

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