Data Guard: Add Standby logfile group tips Oracle Database Tips by Donald Burleson

Oracle Data Guard - Using the Standby Redo Log Files

The concept of the standby redo log files was introduced in Oracle9i. However, this was confined to the physical standby databases only.

With the introduction of support for standby redo logs for logical standby databases in Oracle10g, it is possible to have a logical Oracle instance be a part of a Data Guard configuration running in maximum protection mode. In this way, the Data Guard SQL Apply method offers complete zero-data-loss support.

The archiver process (ARCn) or the log writer process (LGWR) on the primary database can transmit redo data directly to remote standby redo logs. Thus, this process eliminates the need to register partial archived redo logs. Standby redo logs can also be multiplexed using multiple members, improving reliability over archived redo logs.

To create a new group of standby redo logs, use the ALTER DATABASE statement with the add standby logfile group clause. The size of a standby redo log must exactly match the primary database online redo logs.

The following benefits accrue from the standby redo log files:

• During a failover, standby redo logs enable Data Guard to apply more redo data than what is available in the archived redo logs alone.
   

• Standby redo logs are required to implement the maximum protection and maximum availability levels of data protection (no-data-loss) disaster recovery solutions.
  

Using the Standby Redo Log Files

• Standby redo logs are required to implement real time apply.
   

• Standby redo logs are required for cascaded redo log destinations.

With the help of this method, it becomes possible to eliminate the potential need to register partial archived redo logs, and it allows as the configuration of as many cascaded redo log destinations as are needed.