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:
A common problem for people with very active systems who use filesystems to store their datafiles is the error, Thread cannot allocate new log, sequence ; Checkpoint not complete. The most commonly recommended remedies for this situation are either to use larger or more online redologs.
Unfortunately, if checkpoint not complete is a chronic problem, neither of these solutions will eliminate the problem. They may forestall, or even reduce the frequency of the error, but the problem will not be solved.
A common habit among DBAs is to assign large batch jobs that make many changes, or have very large transactions, to a dedicated rollback segment, using the set transaction use rollback segment; command. Many databases have a rollback segment called rbs_large or something similar for this purpose.