Oracle在10g中引入了闪回区(flash recovery area)的概念，用以简化和完善备份，

1.闪回区的使用
为了启用闪回区功能，需要对DB_RECOVERY_FILE_DEST_SIZE和DB_RECOVERY_FILE_DEST 这两个参数进行设置，其中DB_RECOVERY_FILE_DEST_SIZE设置闪回区的大小，

DB_RECOVERY_FILE_DEST设置闪回区的位置。对于归档日志存放位置，如果没有设置log_archive_dest_1，则将使用闪回区来存放归档日志。

SQL> show parameter log_archive_dest_1

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
log_archive_dest_1                   string
log_archive_dest_10                  string

SQL> alter system set db_recovery_file_dest='/ora10g/db_recover_file/EBANK/' scope=both;

System altered.

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     411
Next log sequence to archive   413
Current log sequence           413

如果此时再将闪回区禁用，则归档日志存放路径将存放到$ORACLE_HOME/dbs下：

SQL> alter system set db_recovery_file_dest='' scopt=both;
alter system set db_recovery_file_dest='' scopt=both
                                          *
ERROR at line 1:
ORA-02065: illegal option for ALTER SYSTEM

SQL> c/scopt/scope
  1* alter system set db_recovery_file_dest='' scope=both
SQL> /

System altered.

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /oracle/product/10204/dbs/arch
Oldest online log sequence     411
Next log sequence to archive   413
Current log sequence           413

在实际管理过程中，对于归档日志的存放，最好手动指定位置：

SQL>  alter system set log_archive_dest_1='location=/ora10g/arch' scope=both;

System altered.

SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /ora10g/arch
Oldest online log sequence     411
Next log sequence to archive   413
Current log sequence           413

2.闪回区的监控。

 V$RECOVERY_FILE_DEST and V$FLASH_RECOVERY_AREA_USAGE这两个视图可以对闪回区进行监控

SQL> SELECT * FROM V$RECOVERY_FILE_DEST;

NAME                                               SPACE_LIMIT SPACE_USED SPACE_RECLAIMABLE NUMBER_OF_FILES
-------------------------------------------------- ----------- ---------- ----------------- ---------------
                                                     104857600          0                 0               0
SQL> SELECT * FROM V$FLASH_RECOVERY_AREA_USAGE;

FILE_TYPE    PERCENT_SPACE_USED PERCENT_SPACE_RECLAIMABLE NUMBER_OF_FILES
------------ ------------------ ------------------------- ---------------
CONTROLFILE                   0                         0               0
ONLINELOG                     0                         0               0
ARCHIVELOG                    0                         0               0
BACKUPPIECE                   0                         0               0
IMAGECOPY                     0                         0               0
FLASHBACKLOG                  0                         0               0