Scenario 8: Failover to Target PDB

For situations where a planned role transition is not possible, a failover can be performed instead of a switchover. A failover is typically performed in an emergency situation where the source PDB has failed or is not accessible. During a failover, the specified target PDB is changed to the source role. If the the original source PDB is unavailable or inaccessible but the container database and other PDBs are all functioning correctly, the failover operation is very similar to the switchover operation in the sense that the original source PDB within the container is converted and marked as a physical standby. Recovery, however, is not started and the PDB must be reinstated as a target PDB before any redo from the new source PDB can be applied.

The following commands perform a failover from nyc_sales to bos_sales and then reinstate nyc_sales as a target PDB for bos_sales:

DGMGRL> FAILOVER TO PLUGGABLE DATABASE bos_sales AT boston; 
Verifying conditions for Failover...   
   Source pluggable database is 'NYC_SALES' at database 'newyork' 
Performing failover NOW, please wait... 
   Closing pluggable database 'NYC_SALES'... 
   Converting 'NYC_SALES' to standby role... 
   Waiting for 'BOS_SALES' to recover all redo data... 
   Stopping recovery at 'BOS_SALES'...    
   Converting 'BOS_SALES' to primary role... 
   Opening new primary 'BOS_SALES'... 
   Waiting for redo data from new primary 'BOS_SALES'... 
Failover succeeded, new primary is "BOS_SALES"

After the failover completes, recovery is not started on the failed (original source) PDB. This is true even if the container database is restarted or if the ENABLE DATABASE command is issued at the container database level. The original source PDB is converted from the primary role to the physical standby role and recovery can only be restarted after it has been reinstated as a target standby for the new source PDB. To verify that the failover was successful and confirm the expected states for each PDB, issue the following commands:

DGMGRL> SHOW PLUGGABLE DATABASE bos_sales AT boston; 
Pluggable database - bos_sales at boston 
   Data Guard Role:   Primary 
   Con_ID:            3 
   Active Target:     con_id 3 at newyork needs to be reinstated 
Pluggable Database Status: 
DGM-17450: not protected 

DGMGRL> SHOW PLUGGABLE DATABASE nyc_sales AT newyork; 
Pluggable database - NYC_SALES at newyork 
   Data Guard Role:    Physical Standby   
   Con_ID:             3 
   Source:             (unknown) 
Pluggable Database Status: 
ORA-16661: The standby database must be reinstated.

After any issues with the former source (primary) PDB have been resolved, start recovery on that PDB to reinstate it in the target role to provide protection for the new source PDB:

DGMGRL> EDIT PLUGGABLE DATABASE nyc_sales AT newyork SET STATE=APPLY-ON; 
Succeeded.

Note:

If any issues with former source PDB cannot be resolved, remove the PDB and follow the steps in Scenarios 1-7 to create a new target PDB to protect the new source PDB.

For more information on removing a PDB refer to: Removing a PDB