Undo表空间数据文件损坏

   UNDO表空间数据文件和system表空间数据文件都是数据库的关键数据文件，如果损坏会导致sql执行失败，用户无法登录，甚至实例崩溃等。同样恢复UNDO表空间数据文件也必须在数据库mount状态下进行。

数据库在运行过程中发现UNDO表空间数据文件损坏，此时是无法正常关闭数据库的：

SQL> shutdown immediate;

ORA-01122: database file 3 failed verification check

ORA-01110: data file 3: '/u01/app/oracle/oradata/orcl/undotbs01.dbf'

ORA-01210: data file header is media corrupt

   只能强制关闭数据库，再启动实例到mount状态下，利用备份恢复损坏的数据文件：

步骤:

A、          关闭数据库

SQL> shutdown abort

ORACLE instance shut down.

B、           启动数据库到mount状态

SQL> startup mount;

C、           在RMAN中，执行restore命令还原UNDO表空间数据文件

RMAN> restore datafile '/u01/app/oracle/oradata/orcl/undotbs01.dbf';

Starting restore at 02-DEC-12

using target database control file instead of recovery catalog

allocated channel: ORA_DISK_1

channel ORA_DISK_1: SID=18 device type=DISK

channel ORA_DISK_1: starting datafile backup set restore

channel ORA_DISK_1: specifying datafile(s) to restore from backup set

channel ORA_DISK_1: restoring datafile 00003 to /u01/app/oracle/oradata/orcl/undotbs01.dbf

channel ORA_DISK_1: reading from backup piece /u01/app/oracle/backup/full_ORCL_20121201_6_1.bak

channel ORA_DISK_1: piece handle=/u01/app/oracle/backup/full_ORCL_20121201_6_1.bak tag=TAG20121201T193434

channel ORA_DISK_1: restored backup piece 1

channel ORA_DISK_1: restore complete, elapsed time: 00:00:08

Finished restore at 02-DEC-12

D、          在RMAN中，执行recover database 恢复数据文件。

RMAN> recover database;

Starting recover at 02-DEC-12

using channel ORA_DISK_1

starting media recovery

media recovery complete, elapsed time: 00:00:00

Finished recover at 02-DEC-12

E、           打开数据库，恢复完成

RMAN> alter database open;

database opened

如果在数据库启动时，发现UNDO表空间数据文件损坏，数据库只能启动到mount状态，其恢复方法相同。