取消快速恢复区报错ORA-38775，如下为实际操作过程：
SQL> show parameter db_recovery_file_dest
NAME TYPE VALUE
------------------------------------ ---------------------- ------------------------------
db_recovery_file_dest string /u01/app/oracle/oradata/orcl151/flashback
db_recovery_file_dest_size big integer 6G
SQL> alter system set db_recovery_file_dest='';
alter system set db_recovery_file_dest=''
*
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-38775: cannot disable recovery area - flashback database is enabled
取消快速恢复区，必须先禁用flashback database.
解决步骤如下：
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 3206836224 bytes
Fixed Size 2257520 bytes
Variable Size 1811942800 bytes
Database Buffers 1375731712 bytes
Redo Buffers 16904192 bytes
Database mounted.
SQL> alter database flashback off;
Database altered.
SQL> alter database open;
Database altered.
SQL> alter system set db_recovery_file_dest='';
System altered.
SQL> show parameter db_recovery_file
NAME TYPE VALUE
------------------------------------ ---------------------- ------------------------------
db_recovery_file_dest string
db_recovery_file_dest_size big integer 6G
