从OCP考题里找出来的，暂时未实验
1.Change the value of the DB_RECOVERY_FILE_DEST initialization parameter to a new value.
2.Shut down the instance.
3.Start up the instance and mount the database.
4.Execute the ALTER DATABASE FLASHBACK OFF command.
5.Execute the ALTER DATABASE FLASHBACK ON command.
6.Open the database.
原文：http://www.cnblogs.com/remote-antiquity/p/7100605.html