After configuring data guard, databases would be either primary and standby database role, and we can altered these roles without loss of data or without resetting logs. called switchover and switch back.
Switchover:
Before performing switchover, kindly verify the state of data guard on both the instances by following SQL queries:
SQL> ALTER SESSION SET nls_date_format=’DD-MON-YYYY HH24:MI:SS’;
SQL> SELECT sequence#, first_time, next_time, applied
FROM v$archived_log
ORDER BY sequence#;
…
…
59 08-OCT-14 08-OCT-14 YES
60 08-OCT-14 08-OCT-14 YES
61 08-OCT-14 08-OCT-14 YES
SQL> select dest_name,status,error from v$archive_dest where dest_name=’LOG_ARCHIVE_DEST_2′;
DEST_NAME
STATUS ERROR
LOG_ARCHIVE_DEST_2
VALID
SQL> select message from v$dataguard_status;
Note: This command will give you appropriate message about the data guard current status.
After getting confirmation on data guard smooth activity, we can instantiate switchover activity by issuing following sort of commands:
On Primary database:
Step-1>>
Connect to Primary database and convert primary database to standby.
[[email protected] ~]$ sqlplus / as sysdba
SQL> alter database commit to switchover to standby;
Database altered.
Step-2>>
Shutdown primary database:
SQL> shutdown immediate;
Step-3>>
Startup nomount old primary database as new standby database:
SQL> startup nomount
ORACLE instance started.
Total System Global Area 972898304 bytes
Fixed Size 2219272 bytes
Variable Size 805307128 bytes
Database Buffers 159383552 bytes
Redo Buffers 5988352 bytes
SQL> alter database mount standby database;
Database altered.
SQL> alter database recover managed standby database disconnect from session;
Database altered.
Verify database role on old primary database:
SQL> select name,open_mode,database_role from v$database;
NAME OPEN_MODE DATABASE_ROLE
RTS MOUNTED PHYSICAL STANDBY
On Standby database:
Step-4>>
On original standby database, Convert old standby database to primary database:
[[email protected] ~]$ sqlplus / as sysdba
Step-5>>
Convert old standby database as primary and shutdown database:
SQL> alter database commit to switchover to primary;
Database altered.
SQL> shutdown immediate;
ORA-01109: database not open
Database dismounted.
ORACLE instance shut down.
Step-6>>
Startup old standby database as primary database:
SQL> startup
ORACLE instance started.
Total System Global Area 972898304 bytes
Fixed Size 2219272 bytes
Variable Size 717226744 bytes
Database Buffers 247463936 bytes
Redo Buffers 5988352 bytes
Database mounted.
Database opened.
Verify database role on old standby database:
SQL> select name,open_mode,database_role from v$database;
NAME OPEN_MODE DATABASE_ROLE
RTS READ WRITE PRIMARY
Switch over activity have completed successfully, our old primary database has become standby and old standby database has become primary database.
Note:
To test above switchover activity, generate multiple archive logs on primary database and verify those archive logs being transferred on standby database.
SQL> alter system switch logfile;
Switchback:
To switchback, you have to follow same above mentioned 6 steps.
