Young Generation Collection - Minor Collection

JVM Tutorials - Herong's Tutorial Examples - Version 4.23, by Dr. Herong Yang

JVM Tutorials - Herong's Tutorial Examples

∟Memory Management and Garbage Collectors

∟Young Generation Collection - Minor Collection

This section describes basic steps of a Young Generation Collection, also called a Minor Collection. The Young Generation is divided into 3 areas: Eden, Survivor Space 'From' and Survivor Space 'To'.

In order to make Minor Collections more efficient, the Young Generation in HotSpot is further divided into 3 areas:

Eden - Stores newly allocated objects with a larger space.
Survivor Space "From" - Stores objects that survived at least one Minor Collection with a smaller space.
Survivor Space "To" - Empty space reserved as working space for the garbage collector with same space size as Survivor Space "From".

There are 6 basic steps involved in a Minor Collection:

Determine each object in the Young Generation is live or dead.
Live objects in the Eden area are copied to the Survivor Space "To" area.
Live objects in the Survivor Space "From" area that are old enough to be promoted are copied to the Tenured Generation.
Live objects in the Survivor Space "From" area that are not old enough to be promoted are copied to the Survivor Space "To" area.
Remove all dead objects to make the Eden area and the Survivor Space "From" area empty.
Swap the label between the Survivor Space "From" area and the Survivor Space "To" area, so the Survivor Space "To" area is empty.

The picture below illustrates basic steps of a Minor Collection in HotSpot JVM:
HotSpot Young Generation (Minor) Collection