问题：Dataguard 无法应用redo log，alert无任何报错信息。

现象：Oracle RAC一节点alert无报错信息，另一节报如下错误。

Thu Mar 15 15:26:22 2018
Error 1017 received logging on to the standby

Check that the primary and standby are using a password file
and remote_login_passwordfile is set to SHARED or EXCLUSIVE,
and that the SYS password is same in the password files.
returning error ORA-16191

PING[ARC2]: Heartbeat Failed to connect to standby 'bbdg'. Error is 16191.

处理方法：将无报错节点的密码文件orapwbbsvri1拷贝到报错的节点。

总结：如果sys密码在oracle安装后更改过，则在搭建dataguard的时候必须确保oracle所有节点和dataguard的密码文件是同一个文件。