undo表空间的数据文件丢失，如果没有备份的情况下，而且丢失的undo文件可以置为offline状态后（注意是offline不是recover状态），则可以如下恢复，下边给出一个例子。
undo表空间文件丢失恢复（1）--有备份的情况下恢复：http://blog.itpub.net/26736162/viewspace-1458654/
undo表空间文件丢失恢复（2）--无备份有redo的情况下恢复：http://blog.itpub.net/26736162/viewspace-1458663/
undo表空间文件丢失恢复（3）--无备份无redo的情况下恢复：http://blog.itpub.net/26736162/viewspace-1458750/
[oracle@rhel6_lhr ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Thu Mar 12 18:13:13 2015
Copyright (c) 1982, 2007, Oracle. All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> show parameter undo
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_management string AUTO
undo_retention integer 900
undo_tablespace string UNDOTBS1
SQL>
---这里一致性关闭后重启
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> ho rm /u03/app/oracle/oradata/ora1024g/undotbs01.dbf
SQL> startup;
ORACLE instance started.
Total System Global Area 448790528 bytes
Fixed Size 2084616 bytes
Variable Size 130023672 bytes
Database Buffers 310378496 bytes
Redo Buffers 6303744 bytes
Database mounted.
ORA-01157: cannot identify/lock data file 2 - see DBWR trace file
ORA-01110: data file 2: '/u03/app/oracle/oradata/ora1024g/undotbs01.dbf'
SQL> set line 9999
SQL> col name format a100
SQL> select name,status,enabled from v$datafile;
NAME STATUS ENABLED
---------------------------------------------------------------------------------------------------- ------- ----------
/u03/app/oracle/oradata/ora1024g/system01.dbf SYSTEM READ WRITE
/u03/app/oracle/oradata/ora1024g/undotbs01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/sysaux01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/users01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/example01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/undotbs02.dbf ONLINE READ WRITE
6 rows selected.
SQL>
SQL> alter database datafile 2 offline;
Database altered.
SQL> select name,status,enabled from v$datafile;
NAME STATUS ENABLED
---------------------------------------------------------------------------------------------------- ------- ----------
/u03/app/oracle/oradata/ora1024g/system01.dbf SYSTEM READ WRITE
/u03/app/oracle/oradata/ora1024g/undotbs01.dbf OFFLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/sysaux01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/users01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/example01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/undotbs02.dbf ONLINE READ WRITE
6 rows selected.
SQL>
SQL> alter database open;
Database altered.
SQL>
SQL> set line 9999
SQL> col name format a100
SQL> select name,status,enabled from v$datafile;
NAME STATUS ENABLED
---------------------------------------------------------------------------------------------------- ------- ----------
/u03/app/oracle/oradata/ora1024g/system01.dbf SYSTEM READ WRITE
/u03/app/oracle/oradata/ora1024g/undotbs01.dbf OFFLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/sysaux01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/users01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/example01.dbf ONLINE READ WRITE
/u03/app/oracle/oradata/ora1024g/undotbs02.dbf ONLINE READ WRITE
6 rows selected.
SQL> select segment_name,status,tablespace_name from dba_rollback_segs;
SEGMENT_NAME STATUS TABLESPACE_NAME
------------------------------ ---------------- ------------------------------
SYSTEM ONLINE SYSTEM
_SYSSMU10$ OFFLINE UNDOTBS1
_SYSSMU9$ OFFLINE UNDOTBS1
_SYSSMU8$ OFFLINE UNDOTBS1
_SYSSMU7$ OFFLINE UNDOTBS1
_SYSSMU6$ OFFLINE UNDOTBS1
_SYSSMU5$ OFFLINE UNDOTBS1
_SYSSMU4$ OFFLINE UNDOTBS1
_SYSSMU3$ OFFLINE UNDOTBS1
_SYSSMU2$ OFFLINE UNDOTBS1
_SYSSMU1$ OFFLINE UNDOTBS1
_SYSSMU20$ OFFLINE UNDOTBS2
_SYSSMU19$ OFFLINE UNDOTBS2
_SYSSMU18$ OFFLINE UNDOTBS2
_SYSSMU17$ OFFLINE UNDOTBS2
_SYSSMU16$ OFFLINE UNDOTBS2
_SYSSMU15$ OFFLINE UNDOTBS2
_SYSSMU14$ OFFLINE UNDOTBS2
_SYSSMU13$ OFFLINE UNDOTBS2
_SYSSMU12$ OFFLINE UNDOTBS2
_SYSSMU11$ OFFLINE UNDOTBS2
21 rows selected.
SQL> create undo tablespace undotbs2 datafile '/u03/app/oracle/oradata/ora1024g/undotbs02.dbf' size 5m autoextend on;
Tablespace created.
SQL> alter system set undo_tablespace=undotbs2 scope=spfile;
System altered.
SQL> alter system set undo_management=manual scope=spfile;
System altered.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 448790528 bytes
Fixed Size 2084616 bytes
Variable Size 130023672 bytes
Database Buffers 310378496 bytes
Redo Buffers 6303744 bytes
Database mounted.
Database opened.
SQL>
SQL> drop tablespace UNDOTBS1;
Tablespace dropped.
SQL>
SQL> create undo tablespace undotbs1 datafile '/u03/app/oracle/oradata/ora1024g/undotbs01.dbf' size 50m autoextend on;
Tablespace created.
SQL> alter system set undo_tablespace=UNDOTBS1 scope=spfile;
System altered.
SQL> alter system set undo_management=auto scope=spfile;
System altered.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 448790528 bytes
Fixed Size 2084616 bytes
Variable Size 130023672 bytes
Database Buffers 310378496 bytes
Redo Buffers 6303744 bytes
Database mounted.
Database opened.
SQL> show parameter undo
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_management string AUTO
undo_retention integer 900
undo_tablespace string UNDOTBS1
SQL>