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1. What does failover means ?

A failover is when the primary database is unavailable. Failover is performed only in the event of a catastrophic failure of the primary database, and the failover results in a transition of a standby database to the primary role. The database administrator can configure Data Guard to ensure no data loss.

2. What does switchover mean ?

A switchover is a role reversal between the primary database and one of its standby databases. A switchover ensures no data loss. This is typically done for planned maintenance of the primary system. During a switchover, the primary database transitions to a standby role, and the standby database transitions to the primary role. The transition occurs without having to re-create either database.

3. Configure Connect Time Failover

Connect time failover will reroute incoming connections to the instance that has just become primary. This type of failover should work in cases where the old primary node is down, old primary network is down, old primary listener is down,
or old primary instance is now the standby.

When the old primary network is down, failover functionality is built into the basic layer of Oracle Net. We simply tcp timeout and fail to the next host in the list. 

DBname_alias =
          (DESCRIPTION =
                   (ADDRESS_LIST =
                          (ADDRESS = (PROTOCOL = TCP)(HOST = primary_host)(PORT = 1521))
                          (ADDRESS = (PROTOCOL = TCP)(HOST = standby_host)(PORT = 1521))
                    )
           (CONNECT_DATA =
                          (INSTANCE_NAME=DBname_primary)
                          (SERVICE_NAME = DBname)
           )
           )

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