ORA-16442: ALTER SYSTEM FLUSH REDO TO STANDBY succeeded, but some redo has not been applied.
Cause: The target standby database did not apply all received redo.
Action: Allow the target standby database to apply all redo and then reissue the ALTER SYSTEM FLUSH REDO TO STANDBY statement.
该错误消息表明，Oracle数据库可能处于不一致的状态，主站和备站之间的redo可能不同步，即某些redo无法在备份上过防操作执行。