OutOfMemoryError on the Method Area

JVM Tutorials - Herong's Tutorial Examples - Version 4.23, by Dr. Herong Yang

JVM Tutorials - Herong's Tutorial Examples

∟OutOfMemoryError on the Method Area

This section provides a tutorial example on how to measure the JVM footprint impact on the Method Area expansion and condition of the OutOfMemoryError exception.

The first run of MethodAreaLoadJar.java is on HotSpot 1.8 with default memory configuration:

C:\herong>\progra~1\java\jdk1.8.0\bin\javac MethodAreaLoadJar.java

C:\herong>\progra~1\java\jdk1.8.0\bin\java MethodAreaLoadJar
Total memory: 16252928
 Free memory: 15709328
 Used memory: 543600
Press ENTER key to continue:

Before pressing ENTER key, open another command window and check the JVM footprint and rt.jar file size:

C:\herong>dir \progra~1\java\jdk1.8.0\jre\lib\rt.jar
       62,653,574 rt.jar

C:\herong>tasklist
Image Name      PID Session Name    Session#    Mem Usage
========== ======== ============ =========== ============
java.exe       8324 Console                1     14,720 K

Now press ENTER key to load all classes and check the footprint again:

Loading all classes in: C:\progra~1\java\jdk1.8.0\jre\lib\rt.jar
# of classes loaded: 19575
Total memory: 16318464
 Free memory: 5301240
 Used memory: 11017224
Press ENTER key to continue:

(in the other window)
C:\herong>tasklist
java.exe       8324 Console                1     88,404 K

Then press ENTER key to run gc() and check the footprint again:

Total memory: 16318464
 Free memory: 9614984
 Used memory: 6703480
Press ENTER key to continue:

(in the other window)
C:\herong>tasklist
java.exe       8324 Console                1     88,828 K

The test output tells us that:

Java classes are loaded into the Method Area, not into the Heap.
When classes are loaded into JVM, the footprint expanded with about the same size as the class JAR file size.
The garbage collector does not remove any unused classes from the Method Area.
When classes are loaded into JVM, some permanent objects are created in the Heap. The garbage collector will not remove those permanent objects.

The next run of MethodAreaLoadJar.java is on HotSpot 1.8 with a lower Method Area limit to produce an out of memory condition:

C:\herong>\progra~1\java\jdk1.8.0\bin\java -Xms5m -Xmx7m 
   -XX:MetaspaceSize=20m -XX:MaxMetaspaceSize=30m MethodAreaLoadJar
Total memory: 6094848
 Free memory: 5637912
 Used memory: 456936
Press ENTER key to continue:
Loading all classes in: C:\progra~1\java\jdk1.8.0\jre\lib\rt.jar
Exception in thread "main" java.lang.OutOfMemoryError: Metaspace
   at java.lang.ClassLoader.findBootstrapClass(Native Method)
   at java.lang.ClassLoader.findBootstrapClassOrNull(ClassLoader.ja...

   at java.lang.ClassLoader.loadClass(ClassLoader.java:413)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:411)
   at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
   at MethodAreaLoadJar.loadRtJar(MethodAreaLoadJar.java:31)
   at MethodAreaLoadJar.main(MethodAreaLoadJar.java:10)

Cool. OutOfMemoryError exception on the "Metaspac", the Method Area, happens as expected.

Of course, we can slowly increase the Method Area limit to find out how big the Method Area needs to be to hold all classes in the rt.jar. The answer is 42 MB.

Last update: 2014.

Table of Contents

About This Book

Downloading and Installing JDK 1.8.0 on Windows

Downloading and Installing JDK 1.7.0 on Windows

java.lang.Runtime Class - The JVM Instance

java.lang.System Class - The Operating System

ClassLoader Class - Class Loaders

Class Class - Class Reflections

Sun's JVM - Java HotSpot VM

JRockit JVM 28.2.7 by Oracle Corporation

►JVM Runtime Data Areas