Redo generation and recoverability
The purpose of redo generation is to ensure recoverability. This is the reason why Oracle does not give the DBA a lot of control over redo generation. If the instance crashes, then all the changes within the SGA will be lost. Oracle will then use the redo entries in the online redo log files to bring the database to a consistent state. The cost of maintaining the redo log records is an expensive operation involving latch management operations (CPU) and frequent write access to the redo log files (I/O). You can avoid redo logging for certain operations using the NOLOGGING feature. We will talk more about the NOLOGGING feature in Chapter 2, NOLOGGING Operations.
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