Description of the illustration cncpt327.eps

This diagram shows a ring of extents in an undo segment: E1, E2, E3, and E4. Extents E1-E3 are active extents without space. In the diagram, transaction T1 and T2 both write to E4 and then start writing to E1. E4 is an active extent without space. E1 is a nonactive extent with space.