flash recovery area配置

检查数据库是否开启闪回：

SQL> select flashback_on from v$database;

FLASHBACK_ON
------------------------------------
YES

打开闪回区，必须要将数据库在mount阶段才能开启，否则会报错，如下：

SQL> alter database flashback on;
alter database flashback on
*
ERROR at line 1:
ORA-38759: Database must be mounted by only one instance and not open.

打开闪回区，数据库必须在归档模式下，否则会报错，如下：

SQL> alter database flashback on;
alter database flashback on
*
ERROR at line 1:
ORA-38706: Cannot turn on FLASHBACK DATABASE logging.
ORA-38707: Media recovery is not enabled.

将数据库修改为归档模式：

SQL> alter database archivelog;

Database altered

在mount阶段，在归档模式下，打开闪回区：

SQL> alter database open;

Database altered.

查看数据库能闪回到最早的SCN：

SQL> select oldest_flashback_scn,oldest_flashback_time from v$flashback_database_log;

OLDEST_FLASHBACK_SCN OLDEST_FLASH
-------------------- ------------
	      648133 13-JUL-14

查看配置的基本参数：

SQL> show parameter db_recovery_file

NAME				     TYPE     VALUE
------------------------------------ -------- ------------------------------
db_recovery_file_dest		     string   +RECOVER
db_recovery_file_dest_size	     big inte 2G
				     ger

数据库可以恢复到多少分钟前的，默认是一天

SQL> show parameter flash

NAME				     TYPE     VALUE
------------------------------------ -------- ------------------------------
db_flashback_retention_target	     integer  1440

使用flash back area需要在初始化参数中定义两个参数，db_recovery_file_dest定义的是闪回区的位置，db_recovery_file_dest_size定义的是闪回区的大小，在RAC环境下配置时，需要保证每个节点的值是相同的：

修改这两个参数的时候，可以在线进行修改，如下：

SQL> alter system set db_recovery_file_dest = '+ASM' scope=both;

System altered.

SQL> alter system set db_recovery_file_dest_size='5g' scope=both sid='*';

System altered.

在使用ASM作为闪回区的位置时，只能指定到磁盘组级别，而不能是某个目录，因为ASM使用的是OMF进行管理的，会自动进行目录的创建：

SQL> alter system set db_recovery_file_dest='+recovery/test' scope=both;
alter system set db_recovery_file_dest='+recovery/test' scope=both
*
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-01261: Parameter db_recovery_file_dest destination string cannot be
translated

SQL> alter system set db_recovery_file_dest='+recovery' scope=both;

System altered.

监控闪回区空间的大小使用情况：

SQL> col name format a32 heading 'file name'
SQL> col spc_lmt_mb format 9999.99 heading 'space|limit|(mb)'
SQL>  col spc_usd_mb format 9999.99 heading 'space|limit|(mb)'
SQL> col spc_rcl_mb format 9999.99 heading 'reclm|space|(mb)'
SQL> col spc_usd_mb format 9999.99 heading 'space|used|(mb)'
SQL> col number_of_files format 99999 heading 'files'
SQL>  select name,space_limit/(1024*1024) spc_lmt_mb,space_used/(1024*1024) spc_usd_mb,space_reclaimable/(1024*1024) spc_rcl_mb,number_of_files from v$recovery_file_dest;

				    space    space    reclm
				    limit     used    space
file name			     (mb)     (mb)     (mb)  files
-------------------------------- -------- -------- -------- ------
+recovery			  5120.00   165.20	.00	 5

如果空间使用率到达85%，在alert日志中可以看到waring的日志，如果超过了97%，会记录一条critical warning日志。告警日志查看：

SQL> select reason,object_type,suggested_action from dba_outstanding_alerts;

查看是什么文件占用了空间：

SQL> select * from v$flash_recovery_area_usage;

FILE_TYPE		 PERCENT_SPACE_USED PERCENT_SPACE_RECLAIMABLE  files
------------------------ ------------------ ------------------------- ------
CONTROLFILE				.13			    0	   1
ONLINELOG			       2.93			    0	   3
ARCHIVELOG				  0			    0	   0
BACKUPPIECE				  0			    0	   0
IMAGECOPY				  0			    0	   0
FLASHBACKLOG				.15			    0	   1

6 rows selected.

在oracle11g的默认情况下，归档日志是保存在flash back area中的，因此如果空间不够，那么将会造成归档日志无法归档，从而删除过期的归档日志即可：

使用RMAN删除过期归档日志：

[oracle@kel ~]$ rman target /

Recovery Manager: Release 10.2.0.1.0 - Production on Mon Jul 14 00:08:02 2014

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

connected to target database: OMF (DBID=680034237)

RMAN> crosscheck archivelog all;

using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=154 devtype=DISK
validation succeeded for archived log
archive log filename=+RECOVER/omf/1_1_852236226.dbf recid=1 stamp=852320500
validation succeeded for archived log
archive log filename=+RECOVER/omf/1_2_852236226.dbf recid=2 stamp=852423499
validation succeeded for archived log
archive log filename=+RECOVER/omf/1_3_852236226.dbf recid=3 stamp=852579011
validation succeeded for archived log
archive log filename=+RECOVER/omf/1_4_852236226.dbf recid=4 stamp=852840609
Crosschecked 4 objects

RMAN> delete expired archivelog all;

released channel: ORA_DISK_1
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=154 devtype=DISK
specification does not match any archive log in the recovery catalog