Data Guard switchover切换（Logical Standby Database）

1)Verify it is possible to perform a switchover on the primary database.
SELECT SWITCHOVER_STATUS FROM V$DATABASE;–TO STANDBY/SESSIONS ACTIVE

2)Prepare the current primary database for the switchover
ALTER DATABASE PREPARE TO SWITCHOVER TO LOGICAL STANDBY;–PREPARING SWITCHOVER
ALTER DATABASE PREPARE TO SWITCHOVER CANCEL;–cancel（终止操作）

3)Prepare the target logical standby database for the switchover
ALTER DATABASE PREPARE TO SWITCHOVER TO PRIMARY;
–PREPARING DICTIONARY–>PREPARING SWITCHOVER
ALTER DATABASE PREPARE TO SWITCHOVER CANCEL;–cancel（终止操作）

4)Ensure the current primary database is ready for the future primary
database’s redo stream
SELECT SWITCHOVER_STATUS FROM V$DATABASE;–TO LOGICAL STANDBY

5)Switch the primary database to the logical standby database role
ALTER DATABASE COMMIT TO SWITCHOVER TO LOGICAL STANDBY;

6)Ensure all available redo has been applied to the target logical standby
database that is about to become the new primary database
SELECT SWITCHOVER_STATUS FROM V$DATABASE;–TO PRIMARY

7)Switch the target logical standby database to the primary database role
ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY;

8)Start SQL Apply on the new logical standby database
ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE;