Standby Switchover/Failover Mode

Database Switchover

A database can be in one of two mutually exclusive modes (primary or standby). These roles can be altered at runtime without loss of data or resetting of redo logs. This process is known as a Switchover and can be performed using the following statements:

-- Convert primary database to standby
CONNECT sys/change_on_install@prim1 AS SYSDBA
ALTER DATABASE COMMIT TO SWITCHOVER TO STANDBY;

-- Shutdown primary database
SHUTDOWN IMMEDIATE;

-- Mount old primary database as standby database
STARTUP NOMOUNT PFILE=C:\Oracle\Admin\TSH1\pfile\init.ora
ALTER DATABASE MOUNT STANDBY DATABASE;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE;


-- Convert standby database to primary
CONNECT sys/change_on_install@stby1 AS SYSDBA
ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY;

-- Shutdown standby database
SHUTDOWN IMMEDIATE;

-- Open old standby database as primary
STARTUP PFILE=C:\Oracle\Admin\TSH1\pfile\init.ora

This process has no affect on alternative standby locations. The process of converting the instances back to their original roles is known as a Switchback. The switchback is accomplished by performing another switchover.

Database Failover

Graceful Database Failover occurs when database failover causes a standby database to be converted to a primary database:

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE FINISH;
ALTER DATABASE ACTIVATE STANDBY DATABASE;

This process will recovery all or some of the application data using the standby redo logs, therefore avoiding reinstantiation of other standby databases. If completed successfully, only the primary database will need to be reinstatiated as a standby database.

Forced Database Failover changes one standby database to a primary database. Application data may be lost neccessitating the reinstantiation of the primary and all standby databases.