PermGen Vs MetaSpace

PermGen

 Prior to Java 8 there existed a special space called the ‘Permanent Generation’. This is where the metadata such as classes would go. Also, some additional things like internalized strings were kept in Permgen. Note that Perm Gen is not part of Java Heap memory.Perm Gen is populated by JVM at runtime based on the classes used by the application. Perm Gen also contains Java SE library classes and methods. Perm Gen objects are garbage collected in a full garbage collection.

It actually used to create a lot of trouble to Java developers, since it is quite hard to predict how much space all of that would require. Result of these failed predictions took the form of java.lang.OutOfMemoryError: Permgen space. Unless the cause of such OutOfMemoryError was an actual memory leak, the way to fix this problem was to simply increase the permgen size similar to the following example setting the maximum allowed permgen size to 256 MB:  
java -XX:MaxPermSize=256m com.mycompany.MyApplication


Metaspace

As predicting the need for metadata was a complex and inconvenient exercise, the Permanent Generation was removed in Java 8 in favor of the Metaspace. From this point on, most of the miscellaneous things were moved to regular Java heap.
The class definitions, however, are now loaded into something called Metaspace. It is located in the native memory and does not interfere with the regular heap objects. By default, Metaspace size is only limited by the amount of native memory available to the Java process. This saves developers from a situation when adding just one more class to the application results in the java.lang.OutOfMemoryError: Permgen space. Notice that having such seemingly unlimited space does not ship without costs – letting the Metaspace to grow uncontrollably you can introduce heavy swapping and/or reach native allocation failures instead.
In case you still wish to protect yourself for such occasions you can limit the growth of Metaspace similar to following, limiting Metaspace size to 256 MB:
java -XX:MaxMetaspaceSize=256m com.mycompany.MyApplication

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