Perm Space in Java

It stands for permanent generation.

The permanent generation is special because it holds meta-data describing user classes (classes that are not part of the Java language). Examples of such meta-data are objects describing classes and methods and they are stored in the Permanent Generation. Applications with large code-base can quickly fill up this segment of the heap which will cause java.lang.OutOfMemoryError: PermGen no matter how high your -Xmx and how much memory you have on the machine.

The permanent Generation contains the following class information:

• Methods of a class.
• Names of the classes.
• Constants pool information.
• Object arrays and type arrays associated with a class.
• Internal objects used by JVM.
• Information used for optimization by the compilers.

‘Java.Lang.OutOfMemoryError: PermGen Space’ occurs when JVM needs to load the definition of a new class and there is no enough space in PermGen. The default PermGen Space allocated is 64 MB for server mode and 32 MB for client mode. There could be 2 reasons why PermGen Space issue occurs.

The 1st reason could be your application or your server has too many classes and the existing PermGen Space is not able to accommodate all the classes. And the 2nd reason could be memory leak. How the class definitions that are loaded could can become unused.