Unplanned Failovers

A failover is an unplanned event that assumes the primary database is lost. The standby database is converted to a primary database immediately after all available redo data from the primary is applied.

Recover From an Unplanned Failover

A failover is an unplanned event that assumes the primary database is lost. The standby database is converted to a primary database immediately after all available primary redo logs are applied. You can use flashback and Oracle Data Guard Broker to reinstate the original primary database as a physical standby.

After a failover, the original primary database must be reinstated as a physical standby. Reinstating the original primary database is easier when you have flashback database and Oracle Data Guard Broker enabled.

Step 3 in this example shuts down the primary on-premises database to imitate an unplanned outage. This example uses Oracle Data Guard Broker to reinstate the primary database.

On-premises database: db1
physical standby database instance in the cloud: db1_phx3g7

On the primary on-premises Oracle Exadata Database Machine, log in as sysdba

Display the configuration for the on-premises database.

DGMGRL> show configuration;

The output should look similar to the following:

Configuration - onpremexadr
  Protection Mode: MaxPerformance
  Members:
    db1        - Primary database
    db1_phx3g7 - Physical standby database 
      Warning: ORA-16809: multiple warnings detected for the member
Fast-Start Failover:  Disabled
Configuration Status:
WARNING   (status updated 36 seconds ago)

Connect to the primary on-premises database instance and perform a shutdown to imitate an unplanned outage.
```
bash-4.2$ sqlplus / as sysdba
SQL> shutdown abort;
```
The output should look similar to the following:
```
ORACLE instance shut down.
```

On Oracle Database Exadata Cloud Service, display the configuration for the database instance.

DGMGRL> show configuration;

The output should look similar to the following:

Configuration - onpremexadr
  Protection Mode: MaxPerformance
  Members:
  db1        - Primary database
    Error: ORA-12514: TNS:listener does not currently know of service requested in 
connect descriptor
    db1_phx3g7 - Physical standby database 
Fast-Start Failover:  Disabled
Configuration Status:
ERROR   (status updated 0 seconds ago)

Initiate the failover to the Oracle Database Exadata Cloud Service instance.
```
DGMGRL> > failover to db1_phx3g7;
```
The output should look similar to the following:
```
Performing failover NOW, please wait...
Failover succeeded, new primary is "db1_phx3g7"
```

Display the configuration for the database instance in Oracle Database Exadata Cloud Service.

DGMGRL> show configuration;

The output should look similar to the following:

Configuration - onpremexadr

  Protection Mode: MaxPerformance
  Members:
  db1_phx3g7 - Primary database
    Warning: ORA-16809: multiple warnings detected for the member
    db1        - Physical standby database (disabled)
      ORA-16661: the standby database needs to be reinstated
Fast-Start Failover:  Disabled
Configuration Status:
WARNING   (status updated 28 seconds ago)

On the on-premises Oracle Exadata Database Machine (db1), which is now Standby, start instance on one node.
```
$srvctl start instance -db db1 -instance db11
```
Use the reinstate database command to make the deactivated primary the standby database.
A reinstate makes the old, deactivated primary the standby database, allowing it to receive redo data from the new primary (the activated standby database).
```
DGMGRL> reinstate database db1;
```
The output should look similar to the following:
```
Reinstating database
        "db1", please wait...Reinstatement of database "db1" succeeded
```

Display the configuration for the on-premises database instance.

DGMGRL> show configuration;

The output should look similar to the following:

Configuration - onpremexadr
  Protection Mode: MaxPerformance
  Members:
  db1_phx3g7 - Primary database
    db1        - Physical standby database 
Fast-Start Failover:  Disabled
Configuration Status:
SUCCESS   (status updated 14 seconds ago)

Switch to the on-premises Oracle Exadata Database Machine when needed.