Database Reference
In-Depth Information
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always use the complete failover! the immediate failover is the last-resort-panic button to be avoided
wherever possible.
Caution
Performing a complete failover
The complete failover, which Oracle recommends over the previously discussed immediate failover, is the default.
During a complete failover Oracle will try to salvage as much redo from the primary as possible. This includes a new
Oracle feature, which allows you to manually mount the old primary and flush previously unsent redo. At the time
of this writing there was no Broker support to do so. This might allow for zero data loss, even though the Data Guard
configuration is not set to such a protection mode. If the old primary cannot be mounted this operation cannot take
place for obvious reasons.
The failover itself is executed very rapidly. Consider the below example:
DGMGRL> show configuration
Configuration - fsconfig
Protection Mode: MaxAvailability
Databases:
CDBFSDCA - Primary database
CDBFSDCB - Physical standby database
Fast-Start Failover: DISABLED
Configuration Status:
ORA-12543: TNS:destination host unreachable
ORA-16625: cannot reach database "CDBFSDCA"
DGM-17017: unable to determine configuration status
As you can see the primary database is inaccessible—the listener is down which implies a severe problem with
the host. After a little further investigation it turned out that the whole rack has gone offline due to a problem with
the power supply. After careful consideration and application of standard Business Continuity Plans the decision has
been made to fail over to the standby database. The DBA then enters the failover command as demonstrated below.
The connection to the Broker is initiated on the standby host to the standby database.
DGMGRL> help failover
Changes a standby database to be the primary database
Syntax:
FAILOVER TO <standby database name> [IMMEDIATE];
DGMGRL> failover to "CDBFSDCB";
Performing failover NOW, please wait...
Failover succeeded, new primary is "CDBFSDCB"
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