这次实验模拟一下，Oracle 11g在非归档模式下，且没有备份的条件，进行的日志文件的恢复
这里所有的redo日志都被我删除了，下面是报错和数据库模式：
SQL> startup
ORACLE instance started.
Total System Global Area 845348864 bytes
Fixed Size 1339796 bytes
Variable Size 645926508 bytes
Database Buffers 192937984 bytes
Redo Buffers 5144576 bytes
Database mounted.
ORA-00313: open failed for members of log group 1 of thread 1
ORA-00312: online log 1 thread 1: '/u01/app/oracle/oradata/myorcl/redo1.log'
ORA-27037: unable to obtain file status
Linux Error: 2: No such file or directory
Additional information: 3
ORA-00312: online log 1 thread 1: '/u01/app/oracle/oradata/myorcl/redo01.log'
ORA-27037: unable to obtain file status
Linux Error: 2: No such file or directory
Additional information: 3
SQL> select log_mode,open_mode from v$database;
LOG_MODE OPEN_MODE
------------ --------------------
NOARCHIVELOG MOUNTED
首先，我们要用resetlogs的方法尝试打开数据库：
SQL> alter database open resetlogs;
alter database open resetlogs
*
ERROR at line 1:
ORA-01139: RESETLOGS option only valid after an incomplete database recovery
提示resetlogs这个选项只有在一个不完全数据库恢复后才可以使用，既然这样，我们就给它做一个数据库恢复：
SQL> recover database using backup controlfile;
ORA-00279: change 1736992 generated at 01/18/2014 18:01:56 needed for thread 1
ORA-00289: suggestion :
/u01/app/oracle/product/11.2.0/db_1/ora_log/1_1_837194464.dbf
ORA-00280: change 1736992 for thread 1 is in sequence #1
Specify log: {=suggested | filename | AUTO | CANCEL}
ORA-00308: cannot open archived log
'/u01/app/oracle/product/11.2.0/db_1/ora_log/1_1_837194464.dbf'
ORA-27037: unable to obtain file status
Linux Error: 2: No such file or directory
Additional information: 3
下面，我们再来resetlogs启动数据库:
SQL> alter database open resetlogs;
alter database open resetlogs
*
ERROR at line 1:
ORA-01113: file 1 needs media recovery
ORA-01110: data file 1: '/u01/app/oracle/oradata/myorcl/system01.dbf'
提示要进行介质恢复，因为我们根本没有redo日志，根本没有办法恢复，只能通过添加隐藏参数，让数据库忽略数据一致性验证：
SQL> alter system set "_allow_resetlogs_corruption"=true scope=spfile;
System altered.
SQL> startup force mount;
ORACLE instance started.
Total System Global Area 845348864 bytes
Fixed Size 1339796 bytes
Variable Size 645926508 bytes
Database Buffers 192937984 bytes
Redo Buffers 5144576 bytes
Database mounted.
到这里，再来添加resetlogs选项，来打开数据库：
SQL> alter database open resetlogs;
Database altered.
数据库打开了，但是还没有结束，我们要将修改的隐藏参数修改到默认值，并重新启动数据库：
SQL> alter system reset "_allow_resetlogs_corruption" scope=spfile;
System altered.
SQL> startup force;
ORACLE instance started.
Total System Global Area 845348864 bytes
Fixed Size 1339796 bytes
Variable Size 645926508 bytes
Database Buffers 192937984 bytes
Redo Buffers 5144576 bytes
Database mounted.
Database opened.
SQL> select KSPPINM,KSPPSTVL from x$ksppi a,x$ksppcv b where a.indx=b.indx and ksppinm like '%resetlogs%';
KSPPINM
--------------------------------------------------------------------------------
KSPPSTVL
--------------------------------------------------------------------------------
_no_recovery_through_resetlogs
FALSE
_allow_resetlogs_corruption
FALSE
这里可以看到这个隐藏参数已经变成false了。这就完成了日志文件的恢复。