Notes on ‘Expert Oracle’ — No.9.1: Redo&Undo — Overview

1. Undo

   a. Undo is recorded in the Undo Segment

   b. Used for undo uncommited operations.

   c. When we do undo, we actually run the opposite SQLs.

2. Redo

   a. Redo = Redo Log

      i. Log as Cache in SGA

     ii. Log flused to Disk

   b. Used only for restoring after failure