_smu_debug_mode在AUM下的應用

OS: windows 2000
DB: oracle 10105
AUM/SMU是9i引入的一項新特性
Automatic undo management is undo-tablespace based. You allocate space in the form. of an undo tablespace, instead of allocating many rollback segments in different sizes.
In manual undo management mode, undo space is allocated externally as rollback segments
在AUM模式下，預設不允許對undo segment進行online/offline/drop操作；
SQL> show parameter undo

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string      AUTO—修改引數必須重啟才能生效
undo_retention                       integer     900
undo_tablespace                      string      UNDOTBS1

SQL> select segment_name,status from dba_rollback_segs;

SEGMENT_NAME                   STATUS
------------------------------ ----------------
SYSTEM                         ONLINE
_SYSSMU1$                      ONLINE
_SYSSMU2$                      ONLINE
_SYSSMU3$                      ONLINE
_SYSSMU4$                      ONLINE
_SYSSMU5$                      ONLINE
_SYSSMU6$                      ONLINE
_SYSSMU7$                      ONLINE
_SYSSMU8$                      ONLINE
_SYSSMU9$                      ONLINE
_SYSSMU10$                     ONLINE
_SYSSMU11$                     ONLINE
_SYSSMU12$                     ONLINE
_SYSSMU13$                     OFFLINE
_SYSSMU14$                     OFFLINE
_SYSSMU15$                     OFFLINE
_SYSSMU16$                     OFFLINE
_SYSSMU17$                     OFFLINE
_SYSSMU18$                     OFFLINE
_SYSSMU19$                     OFFLINE
_SYSSMU20$                     OFFLINE
_SYSSMU21$                     OFFLINE
_SYSSMU22$                     OFFLINE

23 rows selected.

SQL> alter rollback segment "_SYSSMU22$" online;

Rollback segment altered.
此時alertlog並不記錄錯誤，但是該segment仍然為offline；
必須設定引數_smu_debug_mode才能在AUM模式下對undo segment進行操作；
alter system set “_smu_debug_mode”=4; --0x00000004    Allow RBU operations to be executed in SMU mode

SQL> alter rollback segment "_SYSSMU22$" online;

Rollback segment altered.
此時undo segment可以正常online