java JVM

1. Generations for Garbage Collection info:

 

Java objects are created in Heap and Heap is divided into three parts, these are called as Young generation, Tenured or Old Generation and Perm Area. 

 

1. young Generation is further divided into three parts known as Eden space, Survivor 1 and Survivor 2 space. When an object first created in heap its gets created in new generation inside Eden space and after subsequent Minor Garbage collection if object survives its gets moved to survivor 1 and then Survivor 2

 

2. before Major Garbage collection moved that object to Old or tenured generation.

 

3. Permanent generation of Heap is somewhat special and it is used to store Meta data related to classes and method in JVM, it also hosts String pool provided by JVM 

 

2.  full GC 

 

a single garbage collector thread that runs concurrently with the application threads with the goal of completing the collection of the tenured generation before it becomes full. In normal operation, the concurrent garbage collector is able to do most of its work with the application threads still running, so only brief pauses are seen by the application threads. if the concurrent garbage collector is unable to finish before the tenured generation fill up, the application is paused with all the application threads stopped. Such Collections with the application stopped are referred as full garbage collections or full GC 

 

http://javarevisited.blogspot.hk/2011/04/garbage-collection-in-java.html