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Expert Oracle Database Architecture, Third Edition by Darl Kuhn, Thomas Kyte

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CHAPTER 9

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Redo and Undo

This chapter describes two of the most important pieces of data in an Oracle database: redo and undo. Redo is the information Oracle records in online (and archived) redo log files in order to “replay” your transaction in the event of a failure. Undo is the information Oracle records in the undo segments in order to reverse, or roll back, your transaction.

In this chapter, we will discuss topics such as how redo and undo (rollback) are generated, and how they fit into transactions, recovery, and so on. We’ll start off with a high-level overview of what redo and undo are and how they work together. We’ll then drill down ...

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