2008.12.22 Server&Instance(SGA,PGA)&database

 

1,Oracle Server

  is a database management system.

  consists of an oracle instance and an oracle database

2,Oracle Instance 中介，手段 

  is a means to access an oracle database

  always opens one and only one database ( Instance 多对一 database)

  Consists of memory(SGA...) and background process structures(PMON, SMON,DBWR...)

Connection & session

 User process

   Connection

 server proces

   session

 Background process:数据库核心的进程

3,database

  is a collection of data that is treated as unit

Consists of three file Types:

 data files;Control files;online redo log files;

other file:

  parameter file

  archived log files(归档文件)

  password file

 

$ ps -ef | grep oracle

$ ls

   controle01.ctl

   redo01.log

   example01.dbf

$  sqlplus /nolog

SQL〉 conn /as sysdba

 Connected  to an idle instance

SQL〉 startup

 oracle instance started

 SGA

SQL〉!

$ps -ef | grep oracle

 

Memory Stucture

Consists of two memory area Known as:

 System Global Area (SGA): allocated at instance start up,and is a fundamental compent of an Oracle instance.（狂消内存）

 Program Global Area(PGA): Allocated when the server proess is started.

$ps -ef | grep oracle

$ipcs  (ipcs 命令 用途 报告进程间通信设施状态。 )

  ---Shared Memory Segments---

SQL〉show sga;