Data standby redo logs Tips Oracle Database Tips by Donald BurlesonDecember 9, 2015

Data Guard Standby Redo Logs

The following features related to standby redo log files are new in Oracle 10g:

• Oracle supports the standby redo logs on a logical standby database, which was not feasible in the previous version of Oracle. As a result, the logical standby database can now be configured in maximum data protection modes such as  MAXIMUM PROTECTION and MAXIMUM AVAILABILITY. The "ALTER DATABASE ADD STANDBY LOGFILE" statement can be used to add standby redo log files on the logical standby database. The usage of this SQL statement is the same for physical and logical standby databases and is described in detail in Chapter 5, "Log Management Services".

Standby Redo Logs

• In Oracle10g, the ARCn process can be configured as the archiving agent when using standby redo log files on remote sites. In this scenario, the archiver process keeps sending the redo logs to remote sites as a redo log is generated on the primary site. As a result, in case of disaster and complete loss of the primary database, the entire redo log worth of data will not be lost because the standby redo log file on standby site will contain some or all of the transactions contained in the lost redo log file. This has been one of the most useful enhancements in Data Guard technology, as it minimizes the loss of data while operating in MAXIMUM PERFORMANCE mode.
   

• In the previous version of Oracle database, the standby redo log file needed to be archived before the transactions embedded in those log files could be applied onto the standby database. Oracle10g provides the ability to configure the log apply service to immediately apply the redo log transaction directly from the standby redo log files. This improves the reporting capabilities from the logical standby database and reduces the down time required for switchover or failover operation. Real-time apply is not the default behavior. The following statements can be executed on the standby site to enable the real-time redo apply feature:

On Physical Standby Database

ALTER DATABASE RECOVER MANAGED Oracle instance USING CURRENT LOGFILE;

On Logical Standby Database

ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE;