Total System Global Area 524288000 bytes
Fixed Size 1220384 bytes
Variable Size 322961632 bytes
Database Buffers 197132288 bytes
Redo Buffers 2973696 bytes
Database mounted.
ORA-00313: open failed for members of log group 3 of thread 1
ORA-00312: online log 3 thread 1: '/u01/app/oracle/oradata/ora10g/redo03.log'
由于启动数据库会检查所有的文件，读取到在线日志文件redo03.log时，就报错了，因为已经被删除
--还原数据库
SYS@ora10g> recover database until cancel;
Media recovery complete.
SYS@ora10g> alter database open;
alter database open
*
ERROR at line 1:
ORA-01589: must use RESETLOGS or NORESETLOGS option for database open
由于之前是正常关闭数据库，在线日志的内容已经写到归档日志文件，利用归档日志进行还原，而还原后的数据库，必须用resetlogs方式来OPEN数据库
SYS@ora10g> alter database open resetlogs;
Database altered.
SYS@ora10g> conn zlm/zlm
Connected.
ZLM@ora10g> select count(*) from t1;
COUNT(*)
----------
20
ZLM@ora10g>
只要是正常关闭数据库的，并且开启了归档，那么即便是删除了current的在线日志，也是可以将数据库重新打开的，并且不会丢失数据（由归档来保证）
测试3：非正常关闭数据库，并删除当前在线日志文件
--添加测试数据后，abort方式关闭数据库
ZLM@ora10g> select group#,thread#,status,archived from v$log;
GROUP# THREAD# STATUS ARC
---------- ---------- ---------------- ---
1 1 CURRENT NO
2 1 UNUSED YES
3 1 INACTIVE YES
ZLM@ora10g> insert into t1 select * from dba_objects where rownum<11;
10 rows created.
ZLM@ora10g> select count(*) from t1;
COUNT(*)
----------
30
ZLM@ora10g> alter system archive log current;
System altered.
ZLM@ora10g> select group#,thread#,status,archived from v$log;
GROUP# THREAD# STATUS ARC
---------- ---------- ---------------- ---
1 1 ACTIVE YES
2 1 CURRENT NO
3 1 INACTIVE YES
ZLM@ora10g> shutdown abort
ORA-01031: insufficient privileges
ZLM@ora10g> conn / as sysdba
Connected.
SYS@ora10g> shutdown abort
ORACLE instance shut down.
SYS@ora10g>
--OS上将current在线日志文件redo02.log删除
[oracle@ora10g ora10g]$ rm -f redo02.log
[oracle@ora10g ora10g]$ ls -l redo*
-rw-r----- 1 oracle oinstall 52429312 Jun 24 11:16 redo01.log
-rw-r----- 1 oracle oinstall 52429312 Jun 24 11:08 redo03.log
--再次启动数据库
SYS@ora10g> startup
ORACLE instance started.
Total System Global Area 524288000 bytes
Fixed Size 1220384 bytes
Variable Size 327155936 bytes
Database Buffers 192937984 bytes
Redo Buffers 2973696 bytes
Database mounted.
ORA-00313: open failed for members of log group 2 of thread 1
ORA-00312: online log 2 thread 1: '/u01/app/oracle/oradata/ora10g/redo02.log'
ORA-27037: unable to obtain file status
Linux Error: 2: No such file or directory
Additional information: 3
SYS@ora10g> alter database clear logfile group 2;
alter database clear logfile group 2
*
ERROR at line 1:
ORA-01624: log 2 needed for crash recovery of instance ora10g (thread 1)
ORA-00312: online log 2 thread 1: '/u01/app/oracle/oradata/ora10g/redo02.log'
SYS@ora10g> recover database until cancel;
ORA-00279: change 1497127 generated at 06/24/2015 11:08:48 needed for thread 1
ORA-00289: suggestion : /u01/app/oracle/flash_recovery_area/ORA10G/archivelog/2015_06_24/o1_mf_1_2_%u_.arc
ORA-00280: change 1497127 for thread 1 is in sequence #2
Specify log: {<RET>=suggested | filename | AUTO | CANCEL}
cancel
ORA-01547: warning: RECOVER succeeded but OPEN RESETLOGS would get error below
ORA-01194: file 1 needs more recovery to be consistent
ORA-01110: data file 1: '/u01/app/oracle/oradata/ora10g/system01.dbf'
ORA-01112: media recovery not started
SYS@ora10g>
之前使用的方法，在此处都不成立，原因是数据库强制要求current的在线日志文件需要crash recover，重新创建自然是不行的，由于是非正常关闭数据库，也没有写入归档文件，当然也无法进行还原，那么此时只有通过别的方法来将数据库OPEN了，当然丢失数据已经是不可避免的了，也就是刚才current在线日志文件中未归档的那部分，即t1表中最后插入的10条记录，权衡利弊，即便是丢数据，也要先将数据库拉起来，那么可以通过设置隐含参数"_allow_resetlogs_corruption=true"来实现
SYS@ora10g> create pfile from spfile;
File created.
SYS@ora10g> show parameter spfile