【oracle】切换undo表空间

1.新建undo表空间
SQL> create undo tablespace undotbs2 datafile 'E:\oracle\product\oradata\orcl\un
dotbs02.dbf' size 10M autoextend on next 10M maxsize 500M;
2.由于undo_tablespace是个动态参数，所以任何时候都可以set。
SQL> alter system set undo_tablespace='undotbs2' scope=both;
系统已更改。
3.查看原来的undo表空间中的undo segment是否都为offline
SQL> select tablespace_name,segment_name,status from dba_rollback_segs;
TABLESPACE_NAME                SEGMENT_NAME                   STATUS
------------------------------ ------------------------------ ----------------
SYSTEM                         SYSTEM                         ONLINE
UNDOTBS1                       _SYSSMU1$                      OFFLINE
UNDOTBS1                       _SYSSMU2$                      OFFLINE
UNDOTBS1                       _SYSSMU3$                      OFFLINE
UNDOTBS1                       _SYSSMU4$                      OFFLINE
UNDOTBS1                       _SYSSMU5$                      OFFLINE
UNDOTBS1                       _SYSSMU6$                      OFFLINE
UNDOTBS1                       _SYSSMU7$                      OFFLINE
UNDOTBS1                       _SYSSMU8$                      OFFLINE
UNDOTBS1                       _SYSSMU9$                      OFFLINE
UNDOTBS1                       _SYSSMU10$                     OFFLINE
UNDOTBS2                       _SYSSMU11$                     ONLINE
UNDOTBS2                       _SYSSMU12$                     ONLINE
UNDOTBS2                       _SYSSMU13$                     ONLINE
UNDOTBS2                       _SYSSMU14$                     ONLINE
UNDOTBS2                       _SYSSMU15$                     ONLINE
UNDOTBS2                       _SYSSMU16$                     ONLINE
UNDOTBS2                       _SYSSMU17$                     ONLINE
UNDOTBS2                       _SYSSMU18$                     ONLINE
UNDOTBS2                       _SYSSMU19$                     ONLINE
TABLESPACE_NAME                SEGMENT_NAME                   STATUS
------------------------------ ------------------------------ ----------------
UNDOTBS2                       _SYSSMU20$                     ONLINE
21 rows selected
原来undotbs1的undo_segment 都为offline，则可以删除undotbs1.
SQL> drop tablespace undotbs1 including contents and datafiles;
表空间已删除。
再次查看：
SQL> select tablespace_name,segment_name,status from dba_rollback_segs;
TABLESPACE_NAME                SEGMENT_NAME                   STATUS
------------------------------ ------------------------------ ----------------
SYSTEM                         SYSTEM                         ONLINE
UNDOTBS2                       _SYSSMU11$                     ONLINE
UNDOTBS2                       _SYSSMU12$                     ONLINE
UNDOTBS2                       _SYSSMU13$                     ONLINE
UNDOTBS2                       _SYSSMU14$                     ONLINE
UNDOTBS2                       _SYSSMU15$                     ONLINE
UNDOTBS2                       _SYSSMU16$                     ONLINE
UNDOTBS2                       _SYSSMU17$                     ONLINE
UNDOTBS2                       _SYSSMU18$                     ONLINE
UNDOTBS2                       _SYSSMU19$                     ONLINE
UNDOTBS2                       _SYSSMU20$                     ONLINE
11 rows selected
SQL> show parameter undo
NAME                                 TYPE        VALUE
------------------------------------ ----------- -----------------------
undo_management                      string      AUTO
undo_retention                       integer     900
undo_tablespace                      string      undotbs2
由于没有offline undotbs1，所以物理删除数据文件的时候报错：
E:\oracle\product\oradata\orcl>del undotbs01.dbf
E:\oracle\product\oradata\orcl\UNDOTBS01.DBF
另一个程序正在使用此文件，进程无法访问。
将oracle的服务关闭后，可以删除。
重新切换，这次先offline，再drop。
SQL> create undo tablespace undotbs1 datafile 'E:\oracle\product\oradata\orcl\undotbs01.dbf' size 10M autoextend on next 10M maxsize 500M;
Tablespace created
SQL> alter system set undo_tablespace='undotbs1' scope=both;
System altered
SQL> select tablespace_name,segment_name,status from dba_rollback_segs;
TABLESPACE_NAME                SEGMENT_NAME                   STATUS
------------------------------ ------------------------------ ----------------
SYSTEM                         SYSTEM                         ONLINE
UNDOTBS1                       _SYSSMU1$                      ONLINE
UNDOTBS1                       _SYSSMU2$                      ONLINE
UNDOTBS1                       _SYSSMU3$                      ONLINE
UNDOTBS1                       _SYSSMU4$                      ONLINE
UNDOTBS1                       _SYSSMU5$                      ONLINE
UNDOTBS1                       _SYSSMU6$                      ONLINE
UNDOTBS1                       _SYSSMU7$                      ONLINE
UNDOTBS1                       _SYSSMU8$                      ONLINE
UNDOTBS1                       _SYSSMU9$                      ONLINE
UNDOTBS1                       _SYSSMU10$                     ONLINE
UNDOTBS2                       _SYSSMU11$                     OFFLINE
UNDOTBS2                       _SYSSMU12$                     OFFLINE
UNDOTBS2                       _SYSSMU13$                     OFFLINE
UNDOTBS2                       _SYSSMU14$                     OFFLINE
UNDOTBS2                       _SYSSMU15$                     OFFLINE
UNDOTBS2                       _SYSSMU16$                     OFFLINE
UNDOTBS2                       _SYSSMU17$                     OFFLINE
UNDOTBS2                       _SYSSMU18$                     OFFLINE
UNDOTBS2                       _SYSSMU19$                     OFFLINE
TABLESPACE_NAME                SEGMENT_NAME                   STATUS
------------------------------ ------------------------------ ----------------
UNDOTBS2                       _SYSSMU20$                     OFFLINE
21 rows selected
SQL> alter tablespace undotbs2 offline;
Tablespace altered
SQL> drop tablespace undotbs2 including contents and datafiles;
Tablespace dropped
SQL> select tablespace_name,segment_name,status from dba_rollback_segs;
TABLESPACE_NAME                SEGMENT_NAME                   STATUS
------------------------------ ------------------------------ ----------------
SYSTEM                         SYSTEM                         ONLINE
UNDOTBS1                       _SYSSMU1$                      ONLINE
UNDOTBS1                       _SYSSMU2$                      ONLINE
UNDOTBS1                       _SYSSMU3$                      ONLINE
UNDOTBS1                       _SYSSMU4$                      ONLINE
UNDOTBS1                       _SYSSMU5$                      ONLINE
UNDOTBS1                       _SYSSMU6$                      ONLINE
UNDOTBS1                       _SYSSMU7$                      ONLINE
UNDOTBS1                       _SYSSMU8$                      ONLINE
UNDOTBS1                       _SYSSMU9$                      ONLINE
UNDOTBS1                       _SYSSMU10$                     ONLINE
11 rows selected
SQL> show parameter undo
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string      AUTO
undo_retention                       integer     900
undo_tablespace                      string      undotbs1
--EOF
原文链接：http://blog.yafeishi.net/2012/09/change-undo-tbs.html