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Oracle Database 12c Backup and Recovery Survival Guide by Aman Sharma, Francisco Munoz Alvarez

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Some other important facts

In this section we will talk about some other important facts about redo that are important for you to know.

Redo and undo for DML

When you issue an insert, update, or delete, Oracle actually makes the change to the data blocks that contain the affected data even though you have not issued a commit. To ensure database integrity, Oracle must write information necessary to reverse the change (undo) into the redo log file to handle any transaction failure or even a rollback. Recovery from media failure is ensured by writing the information necessary to replay all database changes (redo) to the database into the redo log file. So, undo and redo information needs to be written into the transaction log of the RDBMS as a logical ...

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