一： Performing a Failover to a Physical Standby Database

https://docs.oracle.com/cd/E11882_01/server.112/e41134/role_management.htm#SBYDB00625

章节：8.2.2， This section describes how to perform a failover to a physical standby database.

二： activate_standby_db_clause

https://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_1004.htm#i2078537

activate_standby_db_clause

Use the  ACTIVATE  STANDBY  DATABASE clause to convert a standby database into a primary database.

PHYSICAL Specify  PHYSICAL to activate a physical standby database. This is the default.

LOGICAL Specify  LOGICAL to activate a logical standby database. If you have more than one logical standby database, then you should first ensure that the same log data is available on all the standby systems.

FINISH APPLY This clause applies only to logical standby databases. Use it to initiate  terminal apply, which is the application of any remaining redo to bring the logical standby database to the same state as the primary database. When terminal apply is complete, the database completes the switchover from logical standby to primary database.

If you require immediate restoration of the database in spite of data loss, then omit this clause. The database will execute the switchover from logical standby to primary database immediately without terminal apply.

三：Oracle 10g/11g关于activate standby database

https://www.linuxidc.com/Linux/2013-09/90091.htm

http://blog.itpub.net/267265/viewspace-2134546/

四、failover后能够恢复DG

https://blog.csdn.net/shiyu1157758655/article/details/55261193

为了能够在failover后能够恢复DG,需要在主库上开启flashback

关于开启flashback 可以参考：

http://blog.csdn.net/shiyu1157758655/article/details/55095760

如果不开启flashback的话，DG就要重新搭建