Oracle备份恢复中，redo的恢复相对来说还是比较简单的，只要保证每组的成员不止一个，出现问题的几率就相当小，即使出了问题我们也可按照不同的方法将他们恢复，所以如果碰到日志文件损坏，完全不必紧张！按照下面的方法来做，基本上都能搞定！

试验一：用命令清空日志组方法

1、 查看原来表中数据

SQL> conn test/test

Connected.

SQL> select * from test;

       TEL

----------

         1

         2

         3

2、插入新数据

SQL> insert into test values(4);

1 row created.

SQL> commit;

Commit complete.

SQL>

3、 正常关闭数据库

4、 利用os command删除所有redo文件

5、 启动数据库

SQL> startup

ORACLE instance started.

Total System Global Area 353862792 bytes

Fixed Size                   730248 bytes

Variable Size             285212672 bytes

Database Buffers           67108864 bytes

Redo Buffers                 811008 bytes

Database mounted.

ORA-00313: open failed for members of log group 1 of thread 1

ORA-00312: online log 1 thread 1: '/T3/ORACLE/oradata/ORA9/redo01.log'

6、 查看当前日志状态

SQL> select * from v$log;

    GROUP#    THREAD# SEQUENCE#      BYTES    MEMBERS ARC STATUS

---------- ---------- ---------- ---------- ---------- --- ----------------

FIRST_CHANGE# FIRST_TIME

------------- ----------

         1          1          2 104857600          1 YES INACTIVE

       487837 01-9月 -05

         2          1          4 104857600          1 NO CURRENT

       487955 01-9月 -05

         3          1          3 104857600          1 YES INACTIVE

       487839 01-9月 -05

看来redo01.log不是当前日志，对于这类非当前日志可以直接clear,系统会重新自动生成一个redo文件

7、SQL> alter database clear logfile group 1;

Database altered.

7、 继续启动db

SQL> alter database open;

alter database open

*

ERROR at line 1:

ORA-00313: open failed for members of log group 2 of thread 1

ORA-00312: online log 2 thread 1: '/T3/ORACLE/oradata/ORA9/redo02.log'

8、 看来redo也得恢复，但是redo02是当前redo,直接clear是不行的

SQL> alter database clear logfile group 2;

alter database clear logfile group 2

*

ERROR at line 1:

ORA-00350: log 2 of thread 1 needs to be archived

ORA-00312: online log 2 thread 1: '/T3/ORACLE/oradata/ORA9/redo02.log'

9、 按照oracle的某些做法也是不行的

SQL> alter database clear unarchived logfile group 2 unrecoverable datafile;

alter database clear unarchived logfile group 2 unrecoverable datafile

*

ERROR at line 1:

ORA-00313: open failed for members of log group 2 of thread 1

ORA-00312: online log 2 thread 1: '/T3/ORACLE/oradata/ORA9/redo02.log'

ORA-27037: unable to obtain file status

SVR4 Error: 2: No such file or directory

Additional information: 3

10、              尝试从其他冷被分cp过来一个，再作clear,还是不行

SQL> host cp /T3/ORACLE/oradata2/ORA9/redo02.log /T3/ORACLE/oradata/ORA9/

SQL> alter database clear unarchived logfile group 2 unrecoverable datafile;

alter database clear unarchived logfile group 2 unrecoverable datafile

*

ERROR at line 1:

ORA-00322: log 2 of thread 1 is not current copy

ORA-00312: online log 2 thread 1: '/T3/ORACLE/oradata/ORA9/redo02.log'

SQL>

11、              但是对于非当前日志就都可以，下面看看redo03

SQL> alter database clear logfile group 3;

Database altered.

结论：

如果数据库是正常shutdown,非当前日志都可以直接clear来重新生成，而且不丢失数据，因为正常关闭db,数据已经写入dbf文件了。唯独当前日志不可以，当前日志必须用其他方法恢复，不管是不是正常关闭，

方法二：用cancel模式恢复数据库

前面的出错提示，步骤都一样，唯独恢复的方法不一样

SQL> startup

ORACLE instance started.

Total System Global Area 353862792 bytes

Fixed Size                   730248 bytes

Variable Size             285212672 bytes

Database Buffers           67108864 bytes

Redo Buffers                 811008 bytes

Database mounted.

ORA-00313: open failed for members of log group 1 of thread 1

ORA-00312: online log 1 thread 1: '/T3/ORACLE/oradata/ORA9/redo01.log'

看看丢失了哪些redo

SQL> host ls /T3/ORACLE/oradarta/ORA9/redo*

/T3/ORACLE/oradarta/ORA9/redo*: No such file or directory

看来redo都丢了

直接recover

SQL> recover database until cancel;

Media recovery complete.

这个时候redo还没有生成

SQL> host ls /T3/ORACLE/oradata/ORA9/redo*

/T3/ORACLE/oradata/ORA9/redo*: No such file or directory

启动数据库

SQL> alter database open ;

alter database open

*

ERROR at line 1:

ORA-01589: must use RESETLOGS or NORESETLOGS option for database open

SQL> alter database open resetlogs;

Database altered.

（注意，这里必须用resetlogs,否则会错误的

SQL> alter database open noresetlogs;

alter database open noresetlogs

*

ERROR at line 1:

ORA-00313: open failed for members of log group 1 of thread 1

ORA-00312: online log 1 thread 1: '/T3/ORACLE/oradata/ORA9/redo01.log'

SQL>

Resetlogs其实就是根据控制文件让系统自动重新生成redo,如果noresetlog的话，就不会重新生成redo,缺少了文件，db自然无法启动）

SQL> host ls /T3/ORACLE/oradata/ORA9/redo*

/T3/ORACLE/oradata/ORA9/redo01.log /T3/ORACLE/oradata/ORA9/redo02.log /T3/ORACLE/oradata/ORA9/redo03.log

SQL>

检验

SQL> select * from test.test;

       TEL

----------

         1

         2

         3

         4

SQL>

数据一点儿都没有丢失

结论：

如果数据库是正常关闭的，用recover database until cancel可以轻松恢复或者说重新建立所有的redo，不再区分是否是当前日志，而且由于正常关闭，不会丢失任何数据，唯一可能丢失的情况就是如果日志还没有归档

这种恢复方法由于要resetlogs,所以在恢复完成后，日志清零，以前的备份不再起作用，所以建议立即备份

SQL> archive log list;

Database log mode              Archive Mode

Automatic archival             Enabled

Archive destination            /T3/ORACLE/arch

Oldest online log sequence     0

Next log sequence to archive   1

Current log sequence           1

SQL>

实验三：通过重新生成控制文件来恢复redo

前面的都一样，只是处理方法不一样

SQL> startup

ORACLE instance started.

Total System Global Area 353862792 bytes

Fixed Size                   730248 bytes

Variable Size             285212672 bytes

Database Buffers           67108864 bytes

Redo Buffers                 811008 bytes

Database mounted.

ORA-00313: open failed for members of log group 1 of thread 1

ORA-00312: online log 1 thread 1: '/T3/ORACLE/oradata/ORA9/redo01.log'

SQL> alter database backup controlfile to trace;

Database altered.

SQL> shutdown immediate

ORA-01109: database not open

Database dismounted.

ORACLE instance shut down.

SQL>

2、 修改一下刚才生成的那个文件

CREATE CONTROLFILE REUSE DATABASE "ORA9"  RESETLOGS  ARCHIVELOG

-- SET STANDBY TO MAXIMIZE PERFORMANCE

    MAXLOGFILES 50

    MAXLOGMEMBERS 5

    MAXDATAFILES 100

    MAXINSTANCES 1

    MAXLOGHISTORY 226

LOGFILE

 GROUP 1 '/T3/ORACLE/oradata/ORA9/redo01.log' SIZE 100M,

 GROUP 2 '/T3/ORACLE/oradata/ORA9/redo02.log' SIZE 100M,

 GROUP 3 '/T3/ORACLE/oradata/ORA9/redo03.log' SIZE 100M

-- STANDBY LOGFILE

DATAFILE

 '/T3/ORACLE/oradata/ORA9/system01.dbf',

 '/T3/ORACLE/oradata/ORA9/undotbs01.dbf',

 '/T3/ORACLE/oradata/ORA9/cwmlite01.dbf',

 '/T3/ORACLE/oradata/ORA9/drsys01.dbf',

 '/T3/ORACLE/oradata/ORA9/example01.dbf',

 '/T3/ORACLE/oradata/ORA9/indx01.dbf',

 '/T3/ORACLE/oradata/ORA9/odm01.dbf',

 '/T3/ORACLE/oradata/ORA9/tools01.dbf',

 '/T3/ORACLE/oradata/ORA9/users01.dbf',

 '/T3/ORACLE/oradata/ORA9/xdb01.dbf',

 '/T3/ORACLE/oradata/ORA9/test01.dbf'

CHARACTER SET ZHS16GBK

;

另存为一个脚本，运行他

SQL> @clone.sql

Control file created.

SQL> alter database open resetlogs;

Database altered.

SQL>

搞定……………

结论：这种方法的关键是重新创建控制文件，后面的步骤和前面的道理一样的

前面的三种方法都是假设db是正常关闭的，数据已经写入数据库文件中，所以不会由数据存在redo种，所以clear的话也不会有数据丢失