This figure shows the same Oracle Data Guard configuration in three different frames, as described in the following list:
The leftmost frame shows the configuration before fast-start failover occurs. Oracle Data Guard is operating in a steady state, with the primary database transmitting redo data to the target standby database and the observer monitoring the state of the entire configuration.
The center frame shows the configuration during fast-start failover. Disaster strikes the primary database, and its network connections to both the observer and the target standby database are lost. Upon detecting the break in communication, the observer attempts to reestablish a connection with the primary database for the amount of time defined by the FastStartFailoverThreshold property before initiating a fast-start failover. If the observer is unable to regain a connection to the primary database within the specified time, and the target standby database is ready for fast-start failover, then fast-start failover ensues.
The rightmost frame shows the configuration after fast-start failover has occurred. The fast-start failover has completed and the target standby database is running in the primary database role. After the former primary database has been repaired, the observer reestablishes its connection to that database and reinstates it as a new standby database. The new primary database starts transmitting redo data to the new standby database.