数据库从mount到open的过程，是个详细的检查过程，oracle在open过程中会进行很多的检测，数据文件的存在，以及scn一致性等等，其中非常重要的并且大家熟知的有下面两个信息检测：
1：第一次检查数据文件头的检查点计数（chenkpoint cnt）是否和控制文件中的检查点计数（chenkpoint cnt）一致，此步骤主要是用以确认数据文件是否来自同一版本。
2：第二次检查数据文件头的开始scn（checkpoint scn）和控制文件中记录的每个文件的结束scn（stop scn）是否一致，如果两者相同，不需要进行恢复，如果不同，则数据库需要进行恢复。
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以上两个检测，总结起来，第一次是版本一致性检测，第二次是是否需要恢复性的检测。
下面通过具体的操作，来演示上面两个过程的具体实现。
[oracle@www cicro]$ sqlplus "/as sysdba"
SQL*Plus: Release 9.2.0.1.0 - Production on Thu Aug 10 17:17:16 2006
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to:
Oracle9i Release 9.2.0.1.0 - Production
JServer Release 9.2.0.1.0 - Production
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL>quit
Disconnected from Oracle9i Release 9.2.0.1.0 - Production
JServer Release 9.2.0.1.0 - Production
[oracle@www cicro]$ ls
cicrodb.dbf control03.ctl example01.dbf redo02.log test undotbstemp.dbf cicrodb.dbf.bak cwmlite01.dbf indx01.dbf redo03.log tools01.dbf users01.dbf control01.ctl cws33db.dbf odm01.dbf system01.dbf undotbs01.dbf xdb01.dbf control02.ctl drsys01.dbf redo01.log temp01.dbf undotbs02.dbf
[oracle@www cicro]$ cp cicrodb.dbf cicrodb.dbf.old
[oracle@www cicro]$ sqlplus "/as sysdba"
SQL*Plus: Release 9.2.0.1.0 - Production on Thu Aug 10 15:36:32 2006
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to an idle instance.
SQL> startup mount
ORACLE instance started.
Total System Global Area 235999352 bytes
Fixed Size 450680 bytes
Variable Size 201326592 bytes
Database Buffers 33554432 bytes
Redo Buffers 667648 bytes
Database mounted.
SQL> alter session set events 'immediate trace name file_hdrs level 10';
Session altered.
此时，/opt/oracle/oradata/cicro/cicrodb.dbf数据文件头信息如下：
**********************************************************
DATA FILE #11:
(name #15) /opt/oracle/oradata/cicro/cicrodb.dbf
creation size=1280 block size=8192 status=0xe head=15 tail=15 dup=1
tablespace 12, index=12 krfil=11 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:137 scn: 0x0800.0195c4d2 08/10/2006 15:36:04
Stop scn: 0x0800.0195c4d2 08/10/2006 15:36:04
Creation Checkpointed at scn: 0x0000.01213333 12/28/2005 15:28:58
thread:1 rba:(0x60.baf.10)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Offline scn: 0x0800.017b052f prev_range: 0
Online Checkpointed at scn: 0x0800.017b0530 08/02/2006 02:29:36
thread:1 rba:(0x1.2.0)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Hot Backup end marker scn: 0x0000.00000000
以上是控制文件的信息，也就是说信息是从控制文件得到的。
以下信息是读取数据文件头得到的。
aux_file is NOT DEFINED
FILE HEADER:
Software vsn=153092096=0x9200000, Compatibility Vsn=134217728=0x8000000
Db ID=44014079=0x29f99ff, Db Name='CICRO'
Activation ID=0=0x0
Control Seq=1295=0x50f, File size=7680=0x1e00
File Number=11, Blksiz=8192, File Type=3 DATA
Tablespace #12 - CICRO rel_fn:11
Creation at scn: 0x0000.01213333 12/28/2005 15:28:58
Backup taken at scn: 0x0000.00000000 01/01/1988 00:00:00 thread:0
reset logs count:0x239b4610 scn: 0x0800.017b0530 recovered at 08/10/2006 15:18:39
status:0x0 root dba:0x00000000 chkpt cnt: 137 ctl cnt:136
begin-hot-backup file size: 0
Checkpointed at scn: 0x0800.0195c4d2 08/10/2006 15:36:04
thread:1 rba:(0x1a.2ac.10)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Backup Checkpointed at scn: 0x0000.00000000
thread:0 rba:(0x0.0.0)
enabled threads: 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
External cache id: 0x0 0x0 0x0 0x0
Absolute fuzzy scn: 0x0000.00000000
Recovery fuzzy scn: 0x0000.00000000 08/10/2006 14:18:35
Terminal Recovery Stamp scn: 0x0000.00000000 01/01/1988 00:00:00
从以上可以看出，此时数据库数据文件头Checkpoint cnt和控制文件Checkpoint cnt相同。数据文件头的Checkpointed at scn和控制文件中的Checkpointed at scn也相同。
然后在dump出控制文件信息，如下
SQL> alter session set events 'immediate trace name CONTROLF level 10';
Session altered.
也同理找出/opt/oracle/oradata/cicro/cicrodb.dbf文件在控制文件中记录的信息。
***********************************************************
DATA FILE #11:
(name #15) /opt/oracle/oradata/cicro/cicrodb.dbf
creation size=1280 block size=8192 status=0xe head=15 tail=15 dup=1
tablespace 12, index=12 krfil=11 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:137 scn: 0x0800.0195c4d2 08/10/2006 15:36:04
Stop scn: 0x0800.0195c4d2 08/10/2006 15:36:04
Creation Checkpointed at scn: 0x0000.01213333 12/28/2005 15:28:58
thread:1 rba:(0x60.baf.10)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Offline scn: 0x0800.017b052f prev_range: 0
Online Checkpointed at scn: 0x0800.017b0530 08/02/2006 02:29:36
thread:1 rba:(0x1.2.0)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Hot Backup end marker scn: 0x0000.00000000
aux_file is NOT DEFINED
以上可以看到，在正常情况下，控制文件中dump出来的数据文件的scn，和dump数据文件头得到的数据文件scn是一样的，在dump数据文件头得到的信息中，一部分来自与控制文件，一部分来自与数据文件头，
如上说明。
继续往下测试：
SQL> alter database open;
Database altered.
SQL> quit
Disconnected from Oracle9i Release 9.2.0.1.0 - Production
JServer Release 9.2.0.1.0 - Production
[oracle@www cicro]$ sqlplus "/as sysdba"
SQL*Plus: Release 9.2.0.1.0 - Production on Thu Aug 10 15:54:11 2006
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to:
Oracle9i Release 9.2.0.1.0 - Production
JServer Release 9.2.0.1.0 - Production
SQL> alter system switch logfile;
System altered.
SQL> /
System altered.
执行日志切换，然后触发完全检查点，这样checkpoint scn将被更新。
SQL> select * from v$log;
GROUP# THREAD# SEQUENCE# BYTES MEMBERS ARC STATUS
---------- ---------- ---------- ---------- ---------- --- ----------------
FIRST_CHANGE# FIRST_TIM
------------- ---------
1 1 26 104857600 1 YES INACTIVE
8.7961E+12 10-AUG-06
2 1 27 104857600 1 YES INACTIVE
8.7961E+12 10-AUG-06
3 1 28 104857600 1 NO CURRENT
8.7961E+12 10-AUG-06
然后关闭数据库
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> quit
Disconnected from Oracle9i Release 9.2.0.1.0 - Production
JServer Release 9.2.0.1.0 – Production
接下来把原来备份的cicrodb.dbf替换过来。
[oracle@www cicro]$ ls
cicrodb.dbf control02.ctl drsys01.dbf redo01.log temp01.dbf undotbs02.dbf cicrodb.dbf.bak control03.ctl example01.dbf redo02.log test undotbstemp.dbf cicrodb.dbf.old cwmlite01.dbf indx01.dbf redo03.log tools01.dbf users01.dbf control01.ctl cws33db.dbf odm01.dbf system01.dbf undotbs01.dbf xdb01.dbf
[oracle@www cicro]$ mv cicrodb.dbf cicrodb.dbf.new
[oracle@www cicro]$ mv cicrodb.dbf.old cicrodb.dbf
[oracle@www cicro]$ sqlplus "/as sysdba"
SQL*Plus: Release 9.2.0.1.0 - Production on Thu Aug 10 15:57:36 2006
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to an idle instance.
SQL> startup mount
ORACLE instance started.
Total System Global Area 235999352 bytes
Fixed Size 450680 bytes
Variable Size 201326592 bytes
Database Buffers 33554432 bytes
Redo Buffers 667648 bytes
Database mounted.
SQL> alter session set events 'immediate trace name CONTROLF level 10';
Sessionaltered.
以下是dump出来的控制文件中cicrodb.dbf文件的信息。
***********************************************************
DATABASE ENTRY
*********************************************************** (blkno = 0x1, size = 192, max = 1, in-use = 1, last-recid= 0)
DF Version: creation=0x9200000 compatible=0x8000000, Date 09/14/2005 14:01:35
DB Name "CICRO"
Database flags = 0x00404001
Controlfile Creation Timestamp 09/14/2005 14:01:35
Incmplt recovery scn: 0x0000.00000000
Resetlogs scn: 0x0800.017b0530 Resetlogs Timestamp 08/02/2006 02:29:36
Prior resetlogs scn: 0x0000.0123d11d Prior resetlogs Timestamp 12/29/2005 11:52:32
Redo Version: creation=0x9200000 compatable=0x9200000
#Data files = 14, #Online files = 14
Database checkpoint: Thread=1 scn: 0x0800.0195c773
Threads: #Enabled=1, #Open=0, Head=0, Tail=0
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
Max log members = 5, Max data members = 1
Arch list: Head=3, Tail=3, Force scn: 0x0800.0195c20fscn: 0x0800.0195c761
Controlfile Checkpointed at scn: 0x0800.0195c761 08/10/2006 15:56:27
thread:0 rba:(0x0.0.0)
enabled threads: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
***********************************************************
CHECKPOINT PROGRESS RECORDS
***********************************************************
(blkno = 0x4, size = 104, max = 1, in-use = 1, last-recid= 0)
THREAD #1 - status:0x1 flags:0x0 dirty:0
low cache rba:(0xffffffff.ffffffff.ffff) on disk rba:(0x1c.2.0)
on disk scn: 0x0800.0195c761 08/10/2006 15:56:27
resetlogs scn: 0x0800.017b0530 08/02/2006 02:29:36
heartbeat: 598125514 mount id: 73105079
MTTR statistics status: 0
***********************************************************
DATA FILE RECORDS
***********************************************************DATA FILE #11:
(name #15) /opt/oracle/oradata/cicro/cicrodb.dbf
creation size=1280 block size=8192 status=0xe head=15 tail=15 dup=1
tablespace 12, index=12 krfil=11 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:140 scn: 0x0800.0195c773 08/10/2006 15:57:01
Stop scn: 0x0800.0195c773 08/10/2006 15:57:01
Creation Checkpointed at scn: 0x0000.01213333 12/28/2005 15:28:58
thread:1 rba:(0x60.baf.10)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Offline scn: 0x0800.017b052f prev_range: 0
Online Checkpointed at scn: 0x0800.017b0530 08/02/2006 02:29:36
thread:1 rba:(0x1.2.0)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Hot Backup end marker scn: 0x0000.00000000
aux_file is NOT DEFINED
然后在dump出数据文件头信息
SQL> alter session set events 'immediate trace name file_hdrs level 10';
Session altered.
***********************************************************
DATA FILE #11:
(name #15) /opt/oracle/oradata/cicro/cicrodb.dbf
creation size=1280 block size=8192 status=0xe head=15 tail=15 dup=1
tablespace 12, index=12 krfil=11 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:140 scn: 0x0800.0195c773 08/10/2006 15:57:01
Stop scn: 0x0800.0195c773 08/10/2006 15:57:01
Creation Checkpointed at scn: 0x0000.01213333 12/28/2005 15:28:58
thread:1 rba:(0x60.baf.10)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Offline scn: 0x0800.017b052f prev_range: 0
Online Checkpointed at scn: 0x0800.017b0530 08/02/2006 02:29:36
thread:1 rba:(0x1.2.0)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Hot Backup end marker scn: 0x0000.00000000
aux_file is NOT DEFINED
以上信息是来自与控制文件，所以与控制文件信息相同。
以下信息是来自于当前的数据文件头，此时由于cicrodb.dbf是旧的数据文件，就出现问题了。
FILE HEADER:
Software vsn=153092096=0x9200000, Compatibility Vsn=134217728=0x8000000
Db ID=44014079=0x29f99ff, Db Name='CICRO'
Activation ID=0=0x0
Control Seq=1295=0x50f, File size=7680=0x1e00
File Number=11, Blksiz=8192, File Type=3 DATA
Tablespace #12 - CICRO rel_fn:11
Creation at scn: 0x0000.01213333 12/28/2005 15:28:58
Backup taken at scn: 0x0000.00000000 01/01/1988 00:00:00 thread:0
reset logs count:0x239b4610 scn: 0x0800.017b0530 recovered at 08/10/2006 15:18:39
status:0x0 root dba:0x00000000 chkpt cnt: 137 ctl cnt:136
（chkpt cnt: 137是记录checkpoint的执行次数，由于是旧的数据文件，chkpt cnt的值还是原来没有替换cicrodb.dbf以前的状态，所以与dump出来的控制文件中记录的chkpt cnt就出现了不同，此时检测就不能通过。）
begin-hot-backup file size: 0
Checkpointed at scn: 0x0800.0195c4d2 08/10/2006 15:36:04
（此时文件的Checkpointed at scn是在没有替换cicrodb.dbf以前的Checkpointed at scn，与dump出来的控制文件中记录的Checkpointed at scn不相同，因此，open时肯定需要恢复）
thread:1 rba:(0x1a.2ac.10)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
Backup Checkpointed at scn: 0x0000.00000000
thread:0 rba:(0x0.0.0)
enabled threads: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
External cache id: 0x0 0x0 0x0 0x0
Absolute fuzzy scn: 0x0000.00000000
Recovery fuzzy scn: 0x0000.00000000 08/10/2006 14:18:35
Terminal Recovery Stamp scn: 0x0000.00000000 01/01/1988 00:00:00
尝试删除cicrodb.dbf文件，然后dump出来数据文件头信息，看看又是什么情况
SQL> quit
Disconnected from Oracle9i Release 9.2.0.1.0 - Production
JServer Release 9.2.0.1.0 - Production
[oracle@www cicro]$ ls
cicrodb.dbf control02.ctl drsys01.dbf redo01.log temp01.dbf undotbs02.dbf cicrodb.dbf.bak control03.ctl example01.dbf redo02.log test undotbstemp.dbf cicrodb.dbf.new cwmlite01.dbf indx01.dbf redo03.log tools01.dbf users01.dbf control01.ctl cws33db.dbf odm01.dbf system01.dbf undotbs01.dbf xdb01.dbf
[oracle@www cicro]$ mv cicrodb.dbf cicrodb.dbf.nn
[oracle@www cicro]$ sqlplus "/as sysdba"
SQL*Plus: Release 9.2.0.1.0 - Production on Thu Aug 10 16:25:13 2006
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to:
Oracle9i Release 9.2.0.1.0 - Production
JServer Release 9.2.0.1.0 – Production
SQL> alter session set events 'immediate trace name file_hdrs level 10';
Session altered.
SQL>
此时Dump出数据文件头信息，如下：
***********************************************************
DATA FILE #11:
(name #15) /opt/oracle/oradata/cicro/cicrodb.dbf
creation size=1280 block size=8192 status=0xe head=15 tail=15 dup=1
tablespace 12, index=12 krfil=11 prev_file=0
unrecoverable scn: 0x0000.00000000 01/01/1988 00:00:00
Checkpoint cnt:140 scn: 0x0800.0195c773 08/10/2006 15:57:01
Stop scn: 0x0800.0195c773 08/10/2006 15:57:01
Creation Checkpointed at scn: 0x0000.01213333 12/28/2005 15:28:58
thread:1 rba:(0x60.baf.10)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Offline scn: 0x0800.017b052f prev_range: 0
Online Checkpointed at scn: 0x0800.017b0530 08/02/2006 02:29:36
thread:1 rba:(0x1.2.0)
enabled threads: 01000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Hot Backup end marker scn: 0x0000.00000000
aux_file is NOT DEFINED
以上仍就是转自控制文件的信息。
ORA-01157: cannot identify/lock data file 11 - see DBWR trace file
ORA-01110: data file 11: '/opt/oracle/oradata/cicro/cicrodb.dbf'
*** Error 1157 in open/read file # 11 ***
此时就提示ORA-01157错误，也就是数据库open时要报的错误。
继续下面的测试，恢复刚才删除的数据文件，尝试打开数据库：
SQL> quit
Disconnected from Oracle9i Release 9.2.0.1.0 - Production
JServer Release 9.2.0.1.0 - Production
[oracle@www cicro]$ ls
cicrodb.dbf.bak control02.ctl drsys01.dbf redo01.log temp01.dbf undotbs02.dbf cicrodb.dbf.new control03.ctl example01.dbf redo02.log test undotbstemp.dbf cicrodb.dbf.nn cwmlite01.dbf indx01.dbf redo03.log tools01.dbf users01.dbf control01.ctl cws33db.dbf odm01.dbf system01.dbf undotbs01.dbf xdb01.dbf
[oracle@www cicro]$ mv cicrodb.dbf.nn cicrodb.dbf
[oracle@www cicro]$ sqlplus "/as sysdba"
