ORA-01548: 已找到活动回退段'_SYSSMU1$'，终止删除表空间 解决办法
http://smfflynj.itpub.net/post/31928/289863
验证过程：
1 查看所有回滚段信息：
select segment_name,status,tablespace_name from dba_rollback_segs;
SEGMENT_NAME STATUS TABLESPACE_NAME
------------------------------ ---------------- ------------------------------
SYSTEM ONLINE SYSTEM
_SYSSMU1$ NEEDS RECOVERY UNDOTBS1
_SYSSMU2$ NEEDS RECOVERY UNDOTBS1
_SYSSMU3$ NEEDS RECOVERY UNDOTBS1
_SYSSMU4$ NEEDS RECOVERY UNDOTBS1
_SYSSMU5$ NEEDS RECOVERY UNDOTBS1
_SYSSMU6$ NEEDS RECOVERY UNDOTBS1
_SYSSMU7$ NEEDS RECOVERY UNDOTBS1
_SYSSMU8$ NEEDS RECOVERY UNDOTBS1
_SYSSMU9$ NEEDS RECOVERY UNDOTBS1
_SYSSMU10$ NEEDS RECOVERY UNDOTBS1
SEGMENT_NAME STATUS TABLESPACE_NAME
------------------------------ ---------------- ------------------------------
_SYSSMU11$ OFFLINE UNDOTBS2
_S