UNDO表空间下的数据文件被误删除后的处理方法

UNDO表空间下的数据文件被误删除后的处理方法：

操作前备份数据库，以避免更大的损失。
思路：
1、把误删除的数据文件offline
2、正常打开数据库后创建新的UNDO表空间及数据文件
3、修改相应参数指向新的UNDO表空间
4、重新启动数据库验证
5、删除旧的UNDO表空间。


以下为我在虚拟机上模拟的场景：在数据库打开的状态下，用操作系统命令将undo表空间对应的唯一数据文件改名，以模拟数据文件被删除的情况。
关闭数据库
SQL> shutdown immediate;
Database closed.
Database dismounted.
Oracle instance shut down.
启动数据库，报错，提示找不到undo表空间下的数据文件/oradata/orcl/undotbs01.dbf
SQL> startup
ORACLE instance started.


Total System Global Area  536870912 bytes
Fixed Size                    2097624 bytes
Variable Size                  150998568 bytes
Database Buffers          377487360 bytes
Redo Buffers                    6287360 bytes
Database mounted.
ORA-01157: cannot identify/lock data file 2 - see DBWR trace file
ORA-01110: data file 2: '/oradata/orcl/undotbs01.dbf'


将该数据文件offline
SQL> alter database datafile 2 offline
2  ;


Database altered.


正常打开数据库
SQL> alter database open;


Database altered.


显示UNDO相关的参数
SQL> show parameter undo


NAME                                    TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string        AUTO
undo_retention                            integer        900
undo_tablespace                      string        UNDOTBS1
创建新的UNDO表空间
SQL> create undo tablespace undotbs2 datafile '/oradata/orcl/undotbs02.dbf' size 320M;


Tablespace created.


修改UNDO_TABLESPACE参数，指向新创建的UNDO表空间
SQL> alter system set undo_tablespace='undotbs2' scope=spfile;


System altered.
重新启动数据库
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.


SQL> startup 
ORACLE instance started.


Total System Global Area  536870912 bytes
Fixed Size                    2097624 bytes
Variable Size                  150998568 bytes
Database Buffers          377487360 bytes
Redo Buffers                    6287360 bytes
Database mounted.
Database opened.


SQL> select * from v$tablespace;


      TS# NAME                          INC BIG FLA ENC
---------- ------------------------------ --- --- --- ---
        0 SYSTEM                          YES NO  YES
        1 UNDOTBS1                          YES NO  YES
        2 SYSAUX                          YES NO  YES
        3 TEMP                          NO  NO  YES
        4 USERS                          YES NO  YES
        5 HRTBS                          YES NO  YES
        6 DEMO                          YES NO  YES
        8 UNDOTBS2                          YES NO  YES


8 rows selected.
确认UNDO_TABLESPACE参数已修改
SQL> show parameter undo


NAME                                    TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string        AUTO
undo_retention                            integer        900
undo_tablespace                      string        undotbs2

删除旧的UNDO表空间
SQL> drop tablespace undotbs1;

Tablespace dropped.