oracle9i回滚段表空间丢失后的处理方法:

用隐含参数恢复数据库的例子：

具体操作步骤如下：

首先把初init.ora文件里自动管理改为手工管理,然后加入隐含参数:
#undo_management=AUTO
undo_tablespace=UNDOTBS
_corrupted_rollback_segments=(_SYSSMU1$,_SYSSMU2$,_SYSSMU3$,_SYSSMU4$,_SYSSMU5$,_SYSSMU6$,_SYSSMU7$,_SYSSMU8$,_SYSSMU9$,_SYSSMU10$)  

SQL>startup mount  （数据库启动到mount状态)
SQL> alter database datafile 'D:\ORACLE\ORADATA\ORCL\UNDOTBS01.DBF' offline drop；
Database altered.

SQL>alter database open;
Database opened.
SQL> show parameter undo

NAME TYPE VALUE
------------------------------------ ----------- ---------
undo_management string MANUAL
undo_retention integer 900
undo_suppress_errors boolean FALSE
undo_tablespace string UNDOTBS

SQL> drop tablespace undotbs including contents;
Tablespace dropped.

重建undotbs表空间:
SQL> create undo tablespace undotbs datafile 'D:\ORACLE\ORADATA\ORCL\UNDOTBS01.DBF'
size 100M;
Tablespace created.

SQL> shutdown immediate  (关闭数据库)
Database closed.
Database dismounted.
ORACLE instance shut down.

编辑init.ora初始化参数文件,去掉隐含参数，设置
undo_management=AUTO
undo_tablespace=UNDOTBS
保存init.ora文件，然后执行
SQL> startup mount
ORACLE instance mounted.
Total System Global Area 114061244 bytes
Fixed Size 282556 bytes
Variable Size 79691776 bytes
Database Buffers 33554432 bytes
Redo Buffers 532480 bytes
Database mounted.

SQL>alter database datafile 'D:\ORACLE\ORADATA\ORCL\UNDOTBS01.DBF' online;
Database altered.

SQL>alter database open;
Database opened.
SQL> show parameter undo

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_management string AUTO
undo_retention integer 900
undo_suppress_errors boolean FALSE
undo_tablespace string UNDOTBS