undo表空间的数据文件从os直接删除了，数据库还没shutduwn，undo需要恢复。
undo表空间的数据文件从os直接删除了，数据库还没shutduwn，，undo需要恢复。
1，数据库正常运行状态中；
2，rm - fundotbs02.dbf， 数据库在不知情的情况下接着运行，直到有日志错误告警。
fri apr 19 13:27:03 2013
[3942] ora-01554 reason: failed to get txn-enqueue tx-0x000d0000-0x00000000
errors in file /u01/app/oracle/diag/rdbms/ora11g/ora11g/trace/ora11g_smon_3942.trc:
ora-01595: error freeing extent (17) of rollback segment (13))
ora-01554: transaction concurrency limit reached reason:failed to get tx-enqueue params:851968, 0
fri apr 19 13:27:51 2013
errors in file /u01/app/oracle/diag/rdbms/ora11g/ora11g/trace/ora11g_j000_10253.trc:
ora-12012: error on auto execute of job 43
ora-01116: error in opening database file 7
ora-01110: data file 7: '/u01/app/oracle/ora11g/undotbs02.dbf'
ora-27041: unable to open file
linux error: 2: no such file or directory
additional information: 3
errors in file /u01/app/oracle/diag/rdbms/ora11g/ora11g/trace/ora11g_j000_10253.trc:
ora-12012: error on auto execute of job 43
ora-01116: error in opening database file 7
ora-01110: data file 7: '/u01/app/oracle/ora11g/undotbs02.dbf'
ora-27041: unable to open file
linux error: 2: no such file or directory
additional information: 3
3，此时创建spfile也会报错。
 sql> create pfile from spfile;
 create pfile from spfile
 *
 error at line 1:
 ora-01116: error in opening database file 7
 ora-01110: data file 7: '/u01/app/oracle/ora11g/undotbs02.dbf'
 ora-27041: unable to open file
 linux error: 2: no such file or directory
 additional information: 3
 4，此时，注意保留现场，不要随意关闭数据库，查询有哪里undo的段正在使用。
 sql> select * from v$rollname;
        usn name
 ---------- ------------------------------
          0 system
        11 _syssmu11_2087506584$
        12 _syssmu12_1903386335$
        13 _syssmu13_3816552520$
        14 _syssmu14_2728152801$
        15 _syssmu15_2082928664$
        16 _syssmu16_1938921541$
        17 _syssmu17_3062294638$
8 rows selected.
 如果数据库已经强行关闭了，可以查询如下。
 sql> select segment_name,status,tablespace_name from dba_rollback_segs where status='needs recovery';
    segment_name                  status          tablespace_name
 ------------------------------ ---------------- ------------------------------
11 _syssmu11_2087506584$ needs recovery  undotbs2
        12 _syssmu12_1903386335$ needs recovery  undotbs2
        13 _syssmu13_3816552520$ needs recovery  undotbs2
        14 _syssmu14_2728152801$ needs recovery  undotbs2
        15 _syssmu15_2082928664$ needs recovery  undotbs2
        16 _syssmu16_1938921541$ needs recovery  undotbs2
        17 _syssmu17_3062294638$ needs recovery  undotbs2