Chapter 13: Oracle Data Guard 487
Managing Roles??”Switchovers and Failovers
Each database that participates in a Data Guard configuration has a role??”it is either a primary
database or a standby database. At some point, those roles may need to change. For example, if
there is a hardware failure on the primary database??™s server, you may fail over to the standby
database. Depending on your configuration choices, there may be some loss of data during a
failover.
A second type of role change is called a switchover. This occurs when the primary database
switches roles with a standby database, and the standby becomes the new primary database.
During a switchover, there should be no data lost. Switchovers and failovers require manual
intervention by a database administrator.
Switchovers
Switchovers are planned role changes, usually to allow for maintenance activities to be performed
on the primary database server. A standby database is chosen to act as the new primary database,
the switchover occurs, and applications now write their data to the new primary database. At
some later point in time you can switch the databases back to their original roles.
NOTE
You can perform switchovers with either a logical standby database
or a physical standby database; the physical standby database is the
preferred option.
What if you have defined multiple standby databases? When one of the physical standby
databases becomes the new primary database, the other standby databases must be able to
receive their redo log data from the new primary database.
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