ORA-16795: the standby database needs to be re-created
Cause: A switchover or failover operation caused this database to require re-creation. The database was marked for re-creation because it was not a viable standby database for the new primary database. Until this error status is resolved for this database, information about this database and the broker configuration to which it belongs is unavailable to a broker client that is connected to this database. Therefore, all commands directed by that client to this database cannot be completed.
Action: Re-create (or flash back) the standby database. Connect to the primary database in the broker configuration and reenable broker management of that database. Once enabled, it is possible to connect to that standby database and manage it with the broker. Alternatively, many client commands that cannot be completed at the standby database when in this error state can be completed successfully when issued to the primary database. In this case, simply reconnect to the primary database and retry the command.
ORA-16795错误表明，Standby数据库必须重新创建，以便将Primary数据库同步到异地位置。官方解释是，当用户尝试从Primary数据库恢复到Standby数据库时，可能会遇到ORA-16795错误。
常见的案例可能是在Primary数据库的实例上，数据库管理员执行了一些DML（数据操纵语言）和DDL（数据定义语言）操作，而这些操作在当前数据库版本的Standby数据库实例中不可执行。
1）停止Primary和Standby数据库实例
2）删除原始Standby数据库
3）使用RMAN，复制Primary到新的Standby数据库
4）启动Primary和Standby数据库实例
5）将新的Standby数据库添加到Data Guard Broker中
6）完成新数据库的复制，保持Primary和Standby数据库同步