What does -XX MaxPermSize do

Question

Specifically  why would it help to fix a PermGen OutOfMemoryError issue   Also  bonus points for an answer that points me to the documentation on JVM arguments

User · Answer

In Java 8 that parameter is commonly used to print a warning message like this one:

Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=512m; support was removed in 8.0

The reason why you get this message in Java 8 is because Permgen has been replaced by Metaspace to address some of PermGen's drawbacks (as you were able to see for yourself, one of those drawbacks is that it had a fixed size).

FYI: an article on Metaspace: http://java-latte.blogspot.in/2014/03/metaspace-in-java-8.html

User · Answer

-XX PermSize -XX MaxPermSize are used to set size for Permanent Generation    Permanent Generation  The Permanent Generation is where class files are kept  These are the result of compiled classes and JSP pages  If this space is full  it triggers a Full Garbage Collection  If the Full Garbage Collection cannot clean out old unreferenced classes and there is no room left to expand the Permanent Space  an Out-of- Memory error  OOME  is thrown and the JVM will crash

User · Answer

The permanent space is where the classes  methods  internalized strings  and similar objects used by the VM are stored and never deallocated  hence the name    This Oracle article succinctly presents the working and parameterization of the HotSpot GC and advises you to augment this space if you load many classes  this is typically the case for application servers and some IDE like Eclipse        The permanent generation does not have a noticeable impact on garbage   collector performance for most applications  However  some   applications dynamically generate and load many classes  for example    some implementations of JavaServer Pages  JSP  pages  These   applications may need a larger permanent generation to hold the   additional classes  If so  the maximum permanent generation size can   be increased with the command-line option -XX MaxPermSize     Note that this other Oracle documentation lists the other HotSpot arguments   Update   Starting with Java 8  both the permgen space and this setting are gone  The memory model used for loaded classes and methods is different and isn t limited  with default settings   You should not see this error any more

[java] What does -XX:MaxPermSize do?

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