Database Switchover
Using this method you can switch backwards and forwards between the primary and DR servers (e.g. so that the primary can become DR and DR can become primary) without having to rebuild either environment:
On Primary Server:
SQL> alter database commit to switchover to standby;
This may cause the following error to be generated:
ERROR at line 1:
ORA-01093: ALTER DATABASE CLOSE only permitted with no sessions connected
If this does occur then restart the database, as below, before retrying the above command:
SQL> shutdown immediate
SQL> startup
SQL> shutdown immediateSQL> startup nomountSQL> alter database mount standby database;SQL> alter database recover managed standby database disconnect;
The primary server is now configured as a DR standby database.
On DR Server:
SQL> alter database recover managed standby database cancel;SQL> alter database commit to switchover to primary;SQL> shutdown immediateSQL> startup
The DR server is now configured as the primary database.
To switch back you just need to repeat the above process but the other way around (e.g. convert the DR database back to a standby and the primary database back to primary).
Activating a Standby Database
If the primary database is not available the standby database can be converted into the primary database as follows:
SQL> alter database recover managed standby database cancel;SQL> alter database activate standby database;SQL> shutdown immediateSQL> startup
The original primary database is now obsolete and can be rebuilt as a standby database once it is available again.
Opening the Standby Database in Read Only Mode
The standby database can be opened in read only mode for querying and then converted back into a standby database without affecting the primary.
On standby server:
SQL> alter database recover managed standby database cancel;SQL> alter database open read only;
The standby database is now open and available for querying in read only mode.
To put the standby database back into standby mode:
SQL> shutdown immediateSQL> startup nomountSQL> alter database mount standby database;SQL> alter database recover managed standby database disconnect;
How to check whether the Standby Database is in Sync
On the primary server:
SQL> SELECT max(sequence#) AS “PRIMARY” FROM v$log_history;
On the standby server:
SQL> SELECT max(sequence#) AS “STANDBY”, applied
FROM v$archived_log GROUP BY applied;
The standby database is in sync with the primary database if the above PRIMARY value matches the above STANDBY value where applied = ‘YES’.
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