When switching to a standby database, there are two basic scenarios. In one scenario, the switchover is undertaken in an emergency, and due to the unavailability of the primary host or the storage, the final one or two redologs are not available, and therefore cannot be applied to the standby. In such a case, the standby must be activated after incomplete recovery, without applying the last changes from the primary. This scenario is extremely rare.
Many people believe that by setting a segment to NOLOGGING mode, no redo will be generated for DML performed against that segment. In fact, only a limited number of operations can be performed NOLOGGING. According to the Oracle 8i Concepts Guide, only the following operations may take advantage of the NOLOGGING feature: