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'
尝试clear unarchived logfile group ,报错：
SQL>; alter database clear unarchived logfile group 2;
alter database clear unarchived logfile group 2
*
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
看来他是因为找不到这个文件，从有效的备份中cp一个过来看看
SQL>; host cp /T3/ORACLE/oradatabak/redo02* /T3/ORACLE/oradata/ORA9
SQL>; alter database clear unarchived logfile group 2;
Database altered.
搞定……….
9、 按照oracle的某些做法也是可以的
SQL>; alter database clear unarchived logfile group 1 unrecoverable datafile;
Database altered.
10、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，当前日志必须首先从有效的备份中拷贝一个日志文件过来，然后用
alter database clear unarchived logfile group n 或alter database clear unarchived logfile group n,除此之外，还可以用下面的方法来做
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
方法四：修改系统参数方法
1、 插入数据
SQL>; select * from test;
TEL
----------
1
2
3
4
SQL>; insert into test values(5);
1 row created.
SQL>; commit;
Commit complete.
SQL>;
2、 强行关闭
SQL>; shutdown abort
ORACLE instance shut down.
SQL>;
3、 手工模拟删除redo
4、 启动db
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 3 of thread 1
ORA-00312: online log 3 thread 1: '/T3/ORACLE/oradata/ORA9/redo03.log'
ORA-27037: unable to obtain file status
SVR4 Error: 2: No such file or directory
Additional information: 3
5、 尝试使用前3中方法中最简单的
SQL>; recover database until cancel;
ORA-00279: change 550174 generated at 09/02/2005 16:00:19 needed for thread 1
ORA-00289: suggestion : /T3/ORACLE/arch/1_1.dbf
ORA-00280: change 550174 for thread 1 is in sequence #1
Specify log: {
看来不行
6、 修改init.ora，加入一行
_allow_resetlogs_corruption=true
7、 启动with pfile
SQL>; startup
ORACLE instance started.
Total System Global Area 320308312 bytes
Fixed Size 730200 bytes
Variable Size 285212672 bytes
Database Buffers 33554432 bytes
Redo Buffers 811008 bytes
Database mounted.
ORA-01589: must use RESETLOGS or NORESETLOGS option for database open
SQL>; host ls /T3/ORACLE/oradata/ORA9/redo*
/T3/ORACLE/oradata/ORA9/redo*: No such file or directory
SQL>; alter database open resetlogs;
Database altered.
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
8、 检验数据
SQL>; select * from test.test;
TEL
----------
1
2
3
4
SQL>;
看到了吧，我们前面由于执行了SHUTDOWN ABORT,这时候对数据的修改还没有保存到数据文件中，虽然执行了COMMIT,这个时候还在联机日志中，等待CKPT触发DBWR写入DATAFILE,但是这个时候执行了SHUTDOWN ABORT,redo被删除后，里面的信息也就丢了，造成数据丢失
9、 备份，去掉那个参数
试验五：丢失当前日志组的成员
1、SQL>; select * from v$logfile;
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
3 ONLINE
/T3/ORACLE/oradata/ORA9/redo03.log
2 ONLINE
/T3/ORACLE/oradata/ORA9/redo02.log
1 ONLINE
/T3/ORACLE/oradata/ORA9/redo01.log
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
1 ONLINE
/T3/ORACLE/oradata/ORA9/redo01a.log
2 ONLINE
/T3/ORACLE/oradata/ORA9/redo02a.log
3 ONLINE
/T3/ORACLE/oradata/ORA9/redo03a.log
SQL>; select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS
---------- ---------- ---------- ---------- ---------- --- ----------------
FIRST_CHANGE# FIRST_TIME
------------- ----------
1 1 2 104857600 2 YES INACTIVE
554599 02-9月 -05
2 1 3 104857600 2 YES INACTIVE
554601 02-9月 -05
3 1 4 104857600 2 NO CURRENT
554603 02-9月 -05
SQL>;
3、 模拟插入数据
SQL>; conn test/test
Connected.
SQL>; select * from test;
TEL
----------
1
2
3
4
SQL>; insert into test values(5);
1 row created.
SQL>; commit
2 ;
Commit complete.
4、 shutdown db,模拟删除一个当前日志成员
$ cd oradata/ORA9
$ ls redo03*
redo03.log redo03a.log
$ rm redo03a.log
5、 启动db,表面没有错误
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.
Database opened.
SQL>;
6、 查看日至成员
SQL>; select * from v$logfile;
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
3 ONLINE
/T3/ORACLE/oradata/ORA9/redo03.log
2 ONLINE
/T3/ORACLE/oradata/ORA9/redo02.log
1 ONLINE
/T3/ORACLE/oradata/ORA9/redo01.log
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
1 ONLINE
/T3/ORACLE/oradata/ORA9/redo01a.log
2 ONLINE
/T3/ORACLE/oradata/ORA9/redo02a.log
3 INVALID ONLINE
/T3/ORACLE/oradata/ORA9/redo03a.log
7、 删除出问题的联机日志文件
SQL>; alter database drop logfile member '/T3/ORACLE/oradata/ORA9/redo03a.log';
alter database drop logfile member '/T3/ORACLE/oradata/ORA9/redo03a.log'
*
ERROR at line 1:
ORA-01609: log 3 is the current log for thread 1 - cannot drop members
ORA-00312: online log 3 thread 1: '/T3/ORACLE/oradata/ORA9/redo03.log'
ORA-00312: online log 3 thread 1: '/T3/ORACLE/oradata/ORA9/redo03a.log'
SQL>;
看来当前日志成员是不允许删除的
SQL>; alter system switch logfile;
System altered.
SQL>; select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS
---------- ---------- ---------- ---------- ---------- --- ----------------
FIRST_CHANGE# FIRST_TIME
------------- ----------
1 1 5 104857600 2 NO CURRENT
557687 02-9月 -05
2 1 3 104857600 2 YES INACTIVE
554601 02-9月 -05
3 1 4 104857600 2 YES ACTIVE
554603 02-9月 -05
SQL>; alter database drop logfile member '/T3/ORACLE/oradata/ORA9/redo03a.log';
Database altered.
SQL>; alter database add logfile member '/T3/ORACLE/oradata/ORA9/redo03a.log' to group 3;
Database altered.
SQL>; select * from v$logfile;
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
3 ONLINE
/T3/ORACLE/oradata/ORA9/redo03.log
2 ONLINE
/T3/ORACLE/oradata/ORA9/redo02.log
1 ONLINE
/T3/ORACLE/oradata/ORA9/redo01.log
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
1 ONLINE
/T3/ORACLE/oradata/ORA9/redo01a.log
2 ONLINE
/T3/ORACLE/oradata/ORA9/redo02a.log
3 INVALID ONLINE
/T3/ORACLE/oradata/ORA9/redo03a.log
看来还得切换一下日至
SQL>; alter system switch logfile;
System altered.
SQL>; select * from v$logfile;
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
3 ONLINE
/T3/ORACLE/oradata/ORA9/redo03.log
2 ONLINE
/T3/ORACLE/oradata/ORA9/redo02.log
1 ONLINE
/T3/ORACLE/oradata/ORA9/redo01.log
GROUP# STATUS TYPE
---------- ------- -------
MEMBER
--------------------------------------------------------------------------------
1 ONLINE
/T3/ORACLE/oradata/ORA9/redo01a.log
2 ONLINE
/T3/ORACLE/oradata/ORA9/redo02a.log
3 ONLINE
/T3/ORACLE/oradata/ORA9/redo03a.log
至此，大功告成…………….
结论：
只要日志组的member不是一个，出现前面的4种可能性是非常小的，即使出现了也有相应的恢复方法，所以不必惊慌；
如果memer多于1个，即使坏了其中的几个，也不会 影响数据库的正常启动，启动后，再进行相应的操作即可， 所以这个时候每天察看alert.log就显得非常重要了。
Remen