实例当前使用的undo表空间中也可能存在offline undo segment！

无意中发现了这一现象，记录一下...没看到到doc里是否有说明...

SQL> select segment_name,owner,tablespace_name,status,block_id,relative_fno status from dba_rollback_segs;

SEGMENT_NA OWNER TABLESPACE STATUS BLOCK_ID STATUS
---------- ------ ---------- ---------------- ---------- ----------
SYSTEM SYS SYSTEM ONLINE 9 1
_SYSSMU1$ PUBLIC UNDOTBS1 ONLINE 9 2
_SYSSMU2$ PUBLIC UNDOTBS1 ONLINE 25 2
_SYSSMU3$ PUBLIC UNDOTBS1 ONLINE 41 2
_SYSSMU4$ PUBLIC UNDOTBS1 ONLINE 57 2
_SYSSMU5$ PUBLIC UNDOTBS1 ONLINE 73 2
_SYSSMU6$ PUBLIC UNDOTBS1 ONLINE 89 2
_SYSSMU7$ PUBLIC UNDOTBS1 ONLINE 105 2
_SYSSMU8$ PUBLIC UNDOTBS1 ONLINE 121 2
_SYSSMU9$ PUBLIC UNDOTBS1 ONLINE 137 2
_SYSSMU10$ PUBLIC UNDOTBS1 ONLINE 153 2

SEGMENT_NA OWNER TABLESPACE STATUS BLOCK_ID STATUS
---------- ------ ---------- ---------------- ---------- ----------
_SYSSMU11$ PUBLIC UNDOTBS1 OFFLINE 15625 2
_SYSSMU12$ PUBLIC UNDOTBS1 OFFLINE 15641 2
_SYSSMU13$ PUBLIC UNDOTBS1 OFFLINE 15657 2
_SYSSMU14$ PUBLIC UNDOTBS1 OFFLINE 15673 2
_SYSSMU15$ PUBLIC UNDOTBS1 OFFLINE 15689 2
_SYSSMU16$ PUBLIC UNDOTBS1 OFFLINE 15705 2
_SYSSMU17$ PUBLIC UNDOTBS1 OFFLINE 15721 2
_SYSSMU18$ PUBLIC UNDOTBS2 OFFLINE 9 7
_SYSSMU19$ PUBLIC UNDOTBS2 OFFLINE 25 7
_SYSSMU20$ PUBLIC UNDOTBS2 OFFLINE 41 7
_SYSSMU21$ PUBLIC UNDOTBS2 OFFLINE 57 7

SEGMENT_NA OWNER TABLESPACE STATUS BLOCK_ID STATUS
---------- ------ ---------- ---------------- ---------- ----------
_SYSSMU22$ PUBLIC UNDOTBS2 OFFLINE 73 7
_SYSSMU23$ PUBLIC UNDOTBS2 OFFLINE 89 7
_SYSSMU24$ PUBLIC UNDOTBS2 OFFLINE 105 7
_SYSSMU25$ PUBLIC UNDOTBS2 OFFLINE 121 7
_SYSSMU26$ PUBLIC UNDOTBS2 OFFLINE 137 7
_SYSSMU27$ PUBLIC UNDOTBS2 OFFLINE 153 7

28 rows selected.

SQL> show parameter undo

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_management string AUTO
undo_retention integer 900
undo_tablespace string UNDOTBS1
SQL>