sql> !cat /etc/redhat-release
Red Hat Enterprise Linux Server release 6.5 (Santiago)
sql> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
PL/sql Release 11.2.0.4.0 - Production
CORE 11.2.0.4.0 Production
TNS for Linux: Version 11.2.0.4.0 - Production
NLSRTL Version 11.2.0.4.0 - Production
查看当前使用的undo表空间信息
sql> show parameter undo_tablespace
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_tablespace string UNDOTBS1
sql> select tablespace_name,file_id,file_name,round (bytes / (1024 * 1024),0) total_space from dba_data_files where tablespace_name='UNDOTBS1';
TABLESPACE_NAME FILE_ID FILE_NAME TOTAL_SPACE
------------------------------ ---------------------------------------- ---------------------------------------- ----------
UNDOTBS1 3 /u01/app/oracle/oradata/orcl/undotbs01.dbf 60
1、数据库状态静止时（无DML操作期间）执行UNDO表空间切换（由UNDOTBS1切换为UNDOTBS2）
（1）创建新的undo表空间UNDOTBS2
sql> create undo tablespace UNDOTBS2 datafile '/u01/app/oracle/oradata/orcl/undotbs02.dbf' size 10M;
Tablespace created.
（2）切换UNDOTBS2为新的undo表空间
sql> alter system set undo_tablespace = undotbs2 scope=both;
System altered.
（3）此时数据库处于静止状态，无任何DML操作，查看UNDOTBS1已经处于OFFLINE状态
TABLESPACE_NAME STATUS COUNT(*)
------------------------------ ---------------- ----------
UNDOTBS1 OFFLINE 10
SYSTEM ONLINE 1
UNDOTBS2 ONLINE 10
（4）检查确认UNDOTBS1中没有ONLINE的segment
sql> select status,segment_name from dba_rollback_segs where status not in ('OFFLINE') and tablespace_name='UNDOTBS1';
no rows selected
（5）删除旧的UNDOTBS1
sql> Drop tablespace UNDOTBS1 including contents and datafiles;
Tablespace dropped.
（6）至此，undo表空间由UNDOTBS1成功切换为UNDOTBS2 .
2、数据库中有DML操作期间，切换UNDO表空间步骤（由UNDOTBS2切换为UNDOTBS1）
session 1正在执行如下操作：
conn test/test
create table test (name varchar(2));
insert into test values ('zhangsan');
commit;
update test set name='lisi' where name='zhangsan';
此时未提交
session 2开始切换undo表空间操作
（1）确认当前使用的undo表空间
undo_tablespace string UNDOTBS2
（2）查看当前undo表空间的所有SELMENT均为ONLINE状态
STATUS SEGMENT_NAME
---------------- ------------------------------
ONLINE _SYSSMU11_3423735372$
ONLINE _SYSSMU12_567660877$
ONLINE _SYSSMU13_100563780$
ONLINE _SYSSMU14_1447748955$
ONLINE _SYSSMU15_478708454$
ONLINE _SYSSMU16_3309423900$
ONLINE _SYSSMU17_525951688$
ONLINE _SYSSMU18_130984470$
ONLINE _SYSSMU19_3964826557$
ONLINE _SYSSMU20_994913344$
10 rows selected.
（3）创建新的undo表空间UNDOTBS1
sql> create undo tablespace UNDOTBS1 datafile '/u01/app/oracle/oradata/orcl/undotbs01.dbf' size 10M;
（4）设置UNDOTBS1为默认undo表空间
sql> alter system set undo_tablespace = undotbs1 scope=both;
（5）此时检查UNDOTBS2中任然有一个SEGMENT处于ONLINE状态
UNDOTBS1 ONLINE 10
UNDOTBS2 OFFLINE 9
UNDOTBS2 ONLINE 1
故此时不能盲目删除UNDOTBS2表空间，否则将报错或导致数据不一致；甚至会导致数据库故障（或许~大概~有可能。。。）
此时需等待UNDOTBS2变为OFFLINE后才可执行删除该表空间的操作。
等待ing...
（6）此时回到session 1执行commit;，再回到session 2查看UNDOTBS2的状态变为OFFLINE
UNDOTBS2 OFFLINE 10
（7）此时删除UNDOTBS2即可
sql> Drop tablespace UNDOTBS2 including contents and datafiles;
sql> show parameter undo
undo_management string AUTO
undo_retention integer 900
undo_tablespace string UNDOTBS1
（8）至此，undo表空间由UNDOTBS2成功切换为UNDOTBS1
参考文章：IF: How to Switch to a New Undo Tablespace (文档 ID 1951695.1)
转自：http://blog.csdn.net/lk_db/article/details/51219266
原文链接：https://www.f2er.com/oracle/208102.html