undo_retention的值为10800，既3小时。

日终会报错。修改undo_retention为3600。

1、检查UNDO Segment状态:

select usn,xacts,rssize/1024/1024/1024,hwmsize/1024/1024/1024,

shrinks from v$rollstat order by rssize;

2、创建新的UNDO表空间undotbs3

create undo tablespace undotbs3 ×××××;

3、切换UNDO表空间为新的UNDO表空间：

alter system set undo_tablespace=undotbs3 scope=both sid=dbbx2;

4、等待原UNDO表空间所有UNDO SEGMENT OFFLINE 的语句：

select usn ,xacts,status,rssize/1024/1024/1024,

hwmsize/1024/1024/1024,shrinksfrom v$rollstat order by rssize;

5、删除原UNDO表空间：

drop tablespace undotbs2 including contents;