数据库启动之OPEN
1、数据库OPEN模式 start open,默认是此模式，或alter database open；这是数据库正常操作的状态，此状态下，任何合法用户都可以数据库连接和执行正常的数据访问操作。 此时， ORACLE启动实例，并打开控制文件，打开所有联机数据文件，打开所有联机重做日志
1、数据库OPEN模式
start open,默认是此模式，或alter database open；这是数据库正常操作的状态，此状态下，任何合法用户都可以数据库连接和执行正常的数据访问操作。
此时，ORACLE启动实例，并打开控制文件，打开所有联机数据文件，打开所有联机重做日志文件。
此时任何数据文件或联机重做日志文件不存在，ORACLE将返回出错信息。此后ORACLE将检查所有联机数据文件和所有联机重做日志文件能否打开并检查数据一致性，如不一致则由SMON后台进程进行实例恢复。
2.数据库OPEN的几种特殊模式：
alterdatabase read only; 将数据库打开至只读模式。
alterdatabase read write; 恢复至正常模式。
只读模式的数据库可以： 执行查询，使用本地管理的表空间来执行磁盘排序。将数据文件脱机、联机，不能对表空间进行此操作。执行数据文件和表空间的脱机恢复。
数据库的限制模式： 此时只有具有restricted session系统权限的用户才可以登陆,。startup restrict
将已运行的数据库设置为限制模式 alter system enable restricted session; 此时已经登陆的用户将不受影响，未登陆的需要有restricted session系统权限。可以使用ALTER SYSTEM KILL SESSION 'sid,serial#' 杀掉已登陆用户进程。
查询有哪些用户已经登陆：
SQL>select sid,serial#,username,type from v$session where type like '%USER';
3.控制文件重要性
由于控制文件中记录了数据库数据文件、日志文件位置、检查点信息等，在OPEN阶段，ORACLE根据控制文件中记录的 这些信息找到对应文件，然后进行检查点及完整性检查。不存在问题则正常启动数据库。如存在检查点不一致或文件丢失，则需要进行恢复。
4.在OPEN过程吕，ORACLE检查以下两项：
检查数据文件头中检查点计数（checkpoint CNT）是否与控制文件中检查点计数（checkpoint CNT）一致。以此确定数据文件是否来自恢复文件。
如果检查点计数检查通过，数据库进行第二次检查，检查数据文件头的开始SCN和控制文件中记录的该文件的结束SCN是否一致，如果控制文件中记录的结束SCN等于数据文件头的开始SCN，不需要恢复。
关于实例恢复的详细分析：http://blog.csdn.net/haibusuanyun/article/details/17082235
以上两次检查通过后，打开数据库，锁定数据文件，并将每个数据文件的结束SCN设置为无穷大。
下面是实验：
SQL>alter database open;
alterdatabase open
*
第 1 行出现错误:
ORA-01157:无法标识/锁定数据文件 1 - 请参阅 DBWR 跟踪文件
ORA-01110:数据文件 1:'E:\SYSORADATA\SYSTEM01.DBF' ----------------在本文开始部分重命令了这个文件
SQL>host move e:\sysoradata\system01bak.dbf e:\sysoradata\system01.dbf
SQL>alter database open;
数据库已更改。
SQL>select status from v$instance;
STATUS
------------
OPEN
5.OPEN时的ALERT日志中信息---对字符集的判断
日志中红字的Database Characterset is ZHS16GBK 是每次数据库启动时，ORACLE判断控制文件中记录的字符集为数据库中字符集是否相符，相符则记录此条记录。
不相符，则以数据库中字符集为准更新控制文件中字符集信息，产生日志类似：updating Character set in controlfile to ZHS16GBK
第一次因数据文件不存在时的日志：
SunFeb 03 22:44:07 2013
alterdatabase open
SunFeb 03 22:44:07 2013
Errorsin file c:\app\administrator\diag\rdbms\orcl\orcl\trace\orcl_dbw0_988.trc:
ORA-01157:cannot identify/lock data file 1 - see DBWR trace file
ORA-01110:data file 1: 'E:\SYSORADATA\SYSTEM01.DBF'
ORA-27041:unable to open file
OSD-04002:无法打开文件
O/S-Error:(OS 2) 系统找不到指定的文件。
Errorsin file c:\app\administrator\diag\rdbms\orcl\orcl\trace\orcl_ora_324.trc:
ORA-01157:无法标识/锁定数据文件 1 - 请参阅 DBWR 跟踪文件
ORA-01110:数据文件 1:'E:\SYSORADATA\SYSTEM01.DBF'
ORA-1157signalled during: alter database open...
SunFeb 03 22:44:09 2013
Checkerrun found 1 new persistent data failures
恢复数据文件后OPEN日志：
Database Characterset is ZHS16GBK语句在偏后
SunFeb 03 22:45:01 2013
alterdatabase open
SunFeb 03 22:45:01 2013
LGWR:STARTING ARCH PROCESSES
SunFeb 03 22:45:01 2013
ARC0started with pid=19, OS id=420
ARC0:Archival started
LGWR:STARTING ARCH PROCESSES COMPLETE
ARC0:STARTING ARCH PROCESSES
SunFeb 03 22:45:02 2013
ARC1started with pid=21, OS id=2440
SunFeb 03 22:45:02 2013
ARC2started with pid=22, OS id=3216
ARC1:Archival started
ARC2:Archival started
ARC1:Becoming the 'no FAL' ARCH
ARC1:Becoming the 'no SRL' ARCH
ARC2:Becoming the heartbeat ARCH
SunFeb 03 22:45:02 2013
ARC3started with pid=23, OS id=2460
Thread1 opened at log sequence 56
Current log# 8 seq# 56 mem# 0: D:\DISK1\REDO05A.LOG
Current log# 8 seq# 56 mem# 1:D:\DISK2\REDO05B.LOG
Current log# 8 seq# 56 mem# 2: D:\DISK3\REDO05C.LOG
Current log# 8 seq# 56 mem# 3:D:\DISK4\REDO05D.LOG
Current log# 8 seq# 56 mem# 4: D:\DISK5\REDO05E.LOG
Successfulopen of redo thread 1
MTTRadvisory is disabled because FAST_START_MTTR_TARGET is not set
SunFeb 03 22:45:02 2013
SMON:enabling cache recovery
ARC3:Archival started
ARC0:STARTING ARCH PROCESSES COMPLETE
ArchivedLog entry 86 added for thread 1 sequence 53 ID 0x4f44a7a1 dest 1:
Successfullyonlined Undo Tablespace 2.
Verifyingfile header compatibility for 11gtablespace encryption..
Verifying11g file header compatibilityfor tablespace encryption completed
SMON:enabling tx recovery
SunFeb 03 22:45:17 2013
ArchivedLog entry 87 added for thread 1 sequence 54 ID 0x4f44a7a1 dest 1:
ArchivedLog entry 88 added for thread 1 sequence 54 ID 0x4f44a7a1 dest 2:
ArchivedLog entry 89 added for thread 1 sequence 54 ID 0x4f44a7a1 dest 3:
ArchivedLog entry 90 added for thread 1 sequence 54 ID 0x4f44a7a1 dest 4:
ArchivedLog entry 91 added for thread 1 sequence 54 ID 0x4f44a7a1 dest 5:
SunFeb 03 22:45:18 2013
ArchivedLog entry 92 added for thread 1 sequence 55 ID 0x4f44a7a1 dest 1:
ArchivedLog entry 93 added for thread 1 sequence 55 ID 0x4f44a7a1 dest 2:
ArchivedLog entry 94 added for thread 1 sequence 55 ID 0x4f44a7a1 dest 3:
ArchivedLog entry 95 added for thread 1 sequence 55 ID 0x4f44a7a1 dest 4:
ArchivedLog entry 96 added for thread 1 sequence 55 ID 0x4f44a7a1 dest 5:
SunFeb 03 22:45:18 2013
Database Characterset is ZHS16GBK
NoResource Manager plan active
SunFeb 03 22:45:30 2013
Startingbackground process QMNC
SunFeb 03 22:45:30 2013
QMNCstarted with pid=24, OS id=3684
SunFeb 03 22:45:40 2013
Completed: alter database open
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