算法计算规则如下：Arg [c]*4得出一个数值，假设为V_Wrap,
如果Arg [d]=0，则V_Wrap值为需要的level
Arg [d] < 1073741824，V_Wrap+1为需要的level
Arg [d] < 2147483648，V_Wrap+2为需要的level
Arg [d] < 3221225472，V_Wrap+3为需要的level
数据库处于mount状态下，执行:alter session set events '10015 trace name adjust_scn level 1';
再alter database open;
可以检查v$datafile与v$datafile_header的substr(checkpoint_change#,1,14)大小相同
四.归档模式下的red log恢复
1）inactive logfile损坏的情况
session 1:
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS
---------- ---------- ---------- ---------- ---------- --- ----------------
FIRST_CHANGE# FIRST_TIM
------------- ---------
1 1 4 104857600 1 NO CURRENT
1.2792E+13 04-JUN-14
2 1 2 104857600 1 YES INACTIVE
1.2792E+13 04-JUN-14
3 1 3 104857600 1 YES INACTIVE
1.2792E+13 04-JUN-14
SQL> col member for a70
SQL> select * from v$logfile;
GROUP# STATUS TYPE
---------- ------- -------
MEMBER IS_
---------------------------------------------------------------------- ---
3 ONLINE
/kttest1-1_data1/emsdev/redo03.dbf NO
1 ONLINE
/kttest1-1_data1/emsdev/redo01.dbf NO
2 ONLINE
/kttest1-1_data1/emsdev/redo02.dbf NO
session 2:
root@kttest1-1 # dd if=/dev/null of=/kttest1-1_data1/emsdev/redo03.dbf bs=512 count=10
0+0 records in
0+0 records out
在这一步，如果不将数据库进行shutdown，继续进行logfile的切换，那么redo03仍然是可以写的，然而存在潜在风险。
session 1:
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 3207790592 bytes
Fixed Size 2119072 bytes
Variable Size 381586016 bytes
Database Buffers 2818572288 bytes
Redo Buffers 5513216 bytes
Database mounted.
ORA-00320: cannot read file header from log 3 of thread 1
ORA-00312: online log 3 thread 1: '/kttest1-1_data1/emsdev/redo03.dbf'
SQL> alter database clear logfile group 3;
Database altered.
SQL> alter database drop logfile group 3;
Database altered.
SQL> alter database add logfile group 3 ('/kttest1-1_data1/emsdev/redo03.dbf') size 100m reuse;
Database altered.
SQL> alter database open; ++++ 这里地方由于原来旧有的redo03被进程持有，可能句柄未释放，所以仍然报错，重启实例即可.
alter database open
*
ERROR at line 1:
ORA-00320: cannot read file header from log 3 of thread 1
ORA-00312: online log 3 thread 1: '/kttest1-1_data1/emsdev/redo03.dbf'
SQL> startup
ORACLE instance started.
Total System Global Area 3207790592 bytes
Fixed Size 2119072 bytes
Variable Size 381586016 bytes
Database Buffers 2818572288 bytes
Redo Buffers 5513216 bytes
Database mounted.
Database opened.
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS
---------- ---------- ---------- ---------- ---------- --- ----------------
FIRST_CHANGE# FIRST_TIM
------------- ---------
1 1 4 104857600 1 YES INACTIVE
1.2792E+13 04-JUN-14
2 1 2 104857600 1 YES INACTIVE
1.2792E+13 04-JUN-14
3 1 5 104857600 1 NO CURRENT
1.2792E+13 04-JUN-14
SQL> alter system switch logfile;
System altered.
2. 归档模式下current logfile损坏
场景一：
session 1:
SQL> set line 200
SQL> col member for a30
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS FIRST_CHANGE# FIRST_TIM
---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- ---------
1 1 4 104857600 1 YES INACTIVE 1.2792E+13 04-JUN-14
2 1 6 104857600 1 NO CURRENT 1.2792E+13 04-JUN-14
3 1 5 104857600 1 YES INACTIVE 1.2792E+13 04-JUN-14
SQL> select * from v$logfile;
GROUP# STATUS TYPE MEMBER IS_
---------- ------- ------- ------------------------------ ---
3 ONLINE /kttest1-1_data1/emsdev/redo03 NO
.dbf
1 ONLINE /kttest1-1_data1/emsdev/redo01 NO
.dbf
2 ONLINE /kttest1-1_data1/emsdev/redo02 NO
.dbf
session 2:
root@kttest1-1 # dd if=/dev/null of=/kttest1-1_data1/emsdev/redo02.dbf bs=512 count=10
0+0 records in
0+0 records out
session 1:
SQL> shutdown immediate
ORA-03113: end-of-file on communication channel
Process ID: 15430
Session ID: 74 Serial number: 1
SQL> conn /as sysdba
Connected to an idle instance.
SQL> startup
ORACLE instance started.