今天测试手工通过bbed修改undo$中回滚段状态(从status$=5修改为1)[NEEDS RECOVERY 修改为 DELETE],然后尝试删除表空间,发现不能删除
删除表空间提示ORA-01561

SQL> drop tablespace undotbs;
drop tablespace undotbs
*
ERROR at line 1:
ORA-01561: failed to remove all objects in the tablespace specified
SQL> drop tablespace undotbs including contents;
drop tablespace undotbs including contents
*
ERROR at line 1:
ORA-01561: failed to remove all objects in the tablespace specified

查询相关信息

SQL> select ts#,name from v$tablespace;
       TS# NAME
---------- ------------------------------
         0 SYSTEM
         1 SYSAUX
         4 USERS
         6 UNDOTBS
         3 TEMP
SQL> select name,ts#,status$ from undo$;
NAME                                  TS#    STATUS$
------------------------------ ---------- ----------
SYSTEM                                  0          3
_SYSSMU1_3138885392$                    2          1
_SYSSMU2_4228238222$                    2          1
_SYSSMU3_2210742642$                    2          1
_SYSSMU4_1455318006$                    2          1
_SYSSMU5_3787622316$                    2          1
_SYSSMU6_2460248069$                    2          1
_SYSSMU7_1924883037$                    2          1
_SYSSMU8_1909280886$                    2          1
_SYSSMU9_3593450615$                    2          1
_SYSSMU10_2490256178$                   2          1
NAME                                  TS#    STATUS$
------------------------------ ---------- ----------
_SYSSMU11_253524401$                    6          1
_SYSSMU12_842775869$                    6          1
_SYSSMU13_2794767139$                   6          1
_SYSSMU14_2067649841$                   6          1
_SYSSMU15_3270221471$                   6          1
_SYSSMU16_4094338609$                   6          1
_SYSSMU17_709661646$                    6          1
_SYSSMU18_699588262$                    6          1
_SYSSMU19_718640828$                    6          1
_SYSSMU20_3516920665$                   6          1
_SYSSMU21_793796797$                    6          1
NAME                                  TS#    STATUS$
------------------------------ ---------- ----------
_SYSSMU22_3988785920$                   6          1
_SYSSMU23_1828333848$                   6          1
_SYSSMU24_1223218862$                   6          1
_SYSSMU25_2939844199$                   6          1
_SYSSMU26_1317300205$                   6          1
_SYSSMU27_1654033223$                   6          1
_SYSSMU28_3748619502$                   6          1
_SYSSMU29_1868765904$                   6          1
_SYSSMU30_3379578723$                   6          1
31 rows selected.
SQL> select segment_name,status from dba_rollback_segs;
SEGMENT_NAME                   STATUS
------------------------------ ----------------
SYSTEM                         ONLINE

通过这里可以看出,通过bbed的修改,除system回滚段外,其他均已经被标志为delete状态,对于这样的情况,很本能的怀疑是extent或者segment未被清理掉导致

查询EXTENT和SEGMENT

SQL> select SEGMENT_NAME from dba_extents where TABLESPACE_NAME='UNDOTBS';
no rows selected
SQL> select segment_name from dba_segments where  TABLESPACE_NAME='UNDOTBS';
no rows selected
SQL> select count(*) from seg$ where ts#=6;
  COUNT(*)
----------
        10
SQL> select count(*) from seg$ where ts#=2;
  COUNT(*)
----------
         0
SQL> select file#,type# from  seg$ where ts#=6;
     FILE#      TYPE#
---------- ----------
         3         10
         3         10
         3         10
         3         10
         3         10
         3         10
         3         10
         3         10
         3         10
         3         10
10 rows selected.

通过查询我们发现SEG$中含有10条记录,而通过dbms_metadata.get_ddl分析DBA_SEGMENTS是的,得出type为10恰好是TYPE2 UNDO信息.

解决办法
删除掉这些因为手工修改undo$信息导致遗留下来的后遗症对象

SQL> delete from seg$ where ts#=6;
10 rows deleted.
SQL> commit;
Commit complete.
SQL> drop tablespace undotbs ;
Tablespace dropped.

这样的直接修改基表的做法,在一般的情况下非常不建议使用,可能带来系统不稳定.但是在数据库异常处理过程中,可能将成为一个法宝