深入剖析Oracle启动过程内部初始化
1 Oracle启动选项;
Oracle数据库在startup启动时，Oracle将在默认位置$ORACLE_HOME/dbs中查找初始化参数文件；Oracle以下面的顺序在其中寻找合适的初始化文件：
Spfile$ORACLE_SID.ora
Spfile.ora
Init$ORACLE_SID.ora
可以用几种方式启动oracle数据库，不同方式启动将影响启动数据库的程度，启动状态由nomount(数据库未装载)——>mount(数据库完成装载)——>open(数据库打开)
1.1 STARTUP NOMOUNT;
SQL> startup nomount
ORACLE instance started.
Total System Global Area 1603411968 bytes
Fixed Size 2253664 bytes
Variable Size 1375734944 bytes
Database Buffers 218103808 bytes
Redo Buffers 7319552 bytes
Oracle读参数文件，打开实例，启动Oracle后台进程,给Oracle分配SGA。此时数据库状态为未装载。
1.2 ALTER DATABASE MOUNT;
SQL> alter database mount;
Database altered.
Oracle 打开并读取控制文件，获取数据文件和重做日志文件的名称和位置。此时数据库完成装载。
1.3 ALTER DATABASE OPEN;
SQL> alter database open;
Database altered.
Oracle打开数据文件和重做日志文件，至此Oracle可以对外提供服务。
2 通过10046事件查看内部启动过程
SQL> startup nomount;
Total System Global Area 1603411968 bytes
Fixed Size 2253664 bytes
Variable Size 1375734944 bytes
Database Buffers 218103808 bytes
Redo Buffers 7319552 bytes
SQL> oradebug setmypid
Statement processed.
SQL> oradebug tracefile_name
/oracle/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_3682.trc
SQL> alter session set events'10046 trace name context forever,level 12';
Session altered.
SQL> alter database mount;
Database altered.
SQL> alter database open;
Database altered.
查看udump文件
[oracle@rhel6 ~]$ more /oracle/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_3682.trc
Trace file /oracle/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_3682.trc
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
ORACLE_HOME = /oracle/app/oracle/product/11.2.0
System name: Linux
Node name: rhel6
Release: 2.6.32-431.el6.x86_64
Version: #1 SMP Sun Nov 10 22:19:54 EST 2013
Machine: x86_64
VM name: VMWare Version: 6
Instance name: orcl
Oracle数据库mount启动读取控制文件，写日志文件
...
WAIT #140528657591192: nam='control file sequential read' ela= 8 file#=0 block#=1 blocks
=1 obj#=-1 tim=1502627703012561
WAIT #140528657591192: nam='control file sequential read' ela= 2 file#=1 block#=1 blocks
=1 obj#=-1 tim=1502627703012583
WAIT #140528657591192: nam='control file sequential read' ela= 47 file#=0 block#=3 block
s=8 obj#=-1 tim=1502627703012650
WAIT #140528657591192: nam='control file sequential read' ela= 13 file#=1 block#=3 block
s=8 obj#=-1 tim=1502627703012674
...
WAIT #140528657591192: nam='ADR block file read' ela= 847 =0 =0 =0 obj#=-1 tim=150262
7707123048
WAIT #140528657591192: nam='ADR block file read' ela= 576 =0 =0 =0 obj#=-1 tim=150262
7707124068
WAIT #140528657591192: nam='ADR block file read' ela= 562 =0 =0 =0 obj#=-1 tim=150262
7707125013
WAIT #140528657591192: nam='ADR block file read' ela= 473 =0 =0 =0 obj#=-1 tim=150262
7707125891
...
Oracle数据库open过程读取控制文件信息，与读取磁盘数据文件头部进行对比
alter database open
END OF STMT
PARSE #140528657591192:c=0,e=274,p=0,cr=0,cu=0,mis=1,r=0,dep=0,og=1,plh=0,tim=1502627713
479605
WAIT #140528657591192: nam='control file sequential read' ela= 8 file#=0 block#=1 blocks
=1 obj#=-1 tim=1502627713479904
WAIT #140528657591192: nam='control file sequential read' ela= 4 file#=1 block#=1 blocks
=1 obj#=-1 tim=1502627713479922
WAIT #140528657591192: nam='control file sequential read' ela= 2 file#=0 block#=15 block
s=1 obj#=-1 tim=1502627713479931
...
WAIT #140528657591192: nam='Disk file operations I/O' ela= 11 FileOperation=2 fileno=1 f
iletype=2 obj#=-1 tim=1502627713481300
WAIT #140528657591192: nam='Disk file operations I/O' ela= 6 FileOperation=2 fileno=2 fi
letype=2 obj#=-1 tim=1502627713481317
WAIT #140528657591192: nam='Disk file operations I/O' ela= 4 FileOperation=2 fileno=3 fi
letype=2 obj#=-1 tim=1502627713481327
WAIT #140528657591192: nam='Disk file operations I/O' ela= 4 FileOperation=2 fileno=4 fi
letype=2 obj#=-1 tim=1502627713481338
WAIT #140528657591192: nam='Disk file operations I/O' ela= 5 FileOperation=2 fileno=201
filetype=2 obj#=-1 tim=1502627713481351