Saturday, August 6, 2011

2 survivor spaces

-- Annotated Sun documentation --

Java defines two generations: the young generation (sometimes called the "nursery") and the old generation. The young generation consists of an "Eden space" and __two__"survivor spaces." The VM initially assigns all objects to the Eden space, and most objects die there. When it performs a minor GC in Eden, the VM moves any remaining objects from the Eden space to __one__ of the 2 survivor spaces.

The VM moves objects that live long enough in the survivor spaces to the "tenured" space. When the tenured generation fills up, there is a full GC that is often much slower because it involves all live objects.

The permanent generation holds all the reflective data of the virtual machine itself, such as class and method objects.

-- adapted from online article (Covalent) --
1. work work work
2. When EDEN is full -> minor collection copies surviving objects into 1st survivor space
3. work work work
4. Eden is full again -> minor GC again
Copy from Eden to 2nd
Copy from 1st to 2nd
5. If 2nd fills up and objects remain in Eden or 1st, these get copied to the tenured

One survivor space is always empty. Serves as destination for minor collections

6. work work work
7. Major collections occur when the tenured space fills up. Major collections free up Eden and both survivor spaces

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