NonStop Server for Java Programmer's Reference (NSJ 4.2+)

The generations are:
Young (also called new) generation—The JVM allocates objects in the young generation pool. Minor
garbage collection happens when this young generation is full and the JVM is unable to allocate new
objects. The young generation also includes two survivor spaces. One survivor space is empty at any time
and serves as a destination of the next GC operation, which copies the collection of any live objects in Eden
and the other survivor space. Objects are copied between survivor spaces in this way until they are old
enough to be tenuredcopied to the tenured generation.
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Tenured (also called old) generation—The JVM moves objects that survived minor garbage collections from
the young generation to the old generation.
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Permanent generation—Class objects and metadata objects are allocated in permanent generation.●
The young and tenured generations each have an area called "Reserved," which is allocated at initialization and
used when garbage collection does not free sufficient space to satisfy the allocation request. In a Sun Microsystems
implementation, the address range for this area is reserved but memory space is not allocated until it is used.
Managing Generation Size
Several java command options allow you to manage the initial size and maximum size of the combined young
and tenured generations.
-Xms
Sets the initial size for the combined young and tenured generation. The default initial size is 3058 kilobytes
(K). Smaller values lead to shorter but more frequent garbage collections, larger values lead to longer but
less frequent garbage collections. For large server applications, HP recommends that the initial size be equal
to the maximum size.
-Xmx
Sets the maximum size for the combined young and tenured generation. The default maximum size is
64 megabytes (MB).
-XX:MaxPermSize
Sets the maximum size for the permanent generation. The default value for MaxPermSize is 32 MB. The
initial size of the permanent generation PermSize option is ignored.