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对于Oracle体系结构初步理解

Jun 07, 2016 pm 05:29 PM
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对于Oracle体系结构的理解-------初步理解 首先,Oracle体系架构是有一张体系图,我也是从这张图的理解。其实体系架构就是这张图

对于Oracle体系结构的理解-------初步理解

首先,Oracle体系架构是有一张体系图,我也是从这张图的理解。其实体系架构就是这张图,要理解体系架构就必须把这张图搞懂才行。

体系图:

一、oracle服务器组成

rdbma是实现的一套完整的解决方案,包括instance  database

instance :内存结构、后台进程

database:物理文件、文件的逻辑结构

二、内存结构

1、User Process

用户访问数据库建立的回话,访问数据库的方式有:1、直接在本地通过socket访问  2、通过TCP 三次握手建立连接到服务器,这种连接方式需要配置$ORACLE_HOME/NETWORK/ADMIN/TNSNAMES.ORA访问的网络地址 3、通过远程方式连接

2、Seerver Process

服务器进程,客户端向服务器发送一个连接就建立一个服务器进程。由于用户执行的服务要在内存中,所以要把提交的数据从进程读取到内存,即为了达到这一目的,oracle设计了PGA

3、Instance

instance即包括服务器上的各个进程,,为数据库提供服务,一个instance只对应一个database,但是一个database可以有多个instance(这个在特殊情况下才有)。

4、PGA (Programe Global Area)

即程序全局区域,是User Process与数据库建立一个连接时,是由oracle数据库服务器本身自动分配它的内存区域,该区域是为当前用户与数据库建立回话保留的,是私有的内存区域;在创建回话时被分配,结束回话后就会释放回收。

组成:它包括:UGA (User Global Area)和Stack Space

UGA包含:User Session Date、Cursor Status、Sort Area

4、SGA(System Global Area)

即系统全局内存区域,在启动实例时被分配,主要用于存储数据库信息的内存区,该信息被进程共享,而从上面的图中可以看到,SGA其中又有:Shared Pool、Database Buffer Cache、Java Pool、Redo Log Buffer、Large Pool,而且共享池里面又有Library Cache、Data Dictionary Cache;共享池里面主要用于缓存被执行SQL语句和被调用的数据定义。在高速缓冲区里面存放数据库用过的数据块(即用户的高速缓冲区),而高速缓冲区又分为三个区:脏数据区(Dirty Buffers)、自由区(Free Buffers)、保留区(Pinned Buffers)

5、介绍用户进程执行一个SQL查询语句时,由用户提交给服务器,再由服务器返回给用户的过程。

a.用户进程先与服务器建立连接

b.建立连接之后,用户把数据提交给服务器进程,服务器进程把数据信息提交给PGA中的UGA中

c.信息通过UGA处理之后传递给instance

d.intance中的共享池负责处理这条语句,library cache负责判断是硬分析还是软分析

e.根据cdo(优化器)得到执行计划准备执行语句,过程是:先在数据字典缓存区查询语句中的对象放在哪个表空间,指定的行放在哪个块里面。

f.开始执行,由于这个执行需要在内存中执行,所以在执行前还需要判断在数据缓存区data buffer cache中是否已经缓存了需要执行的块?如果是,则在内存中读取到数据得到需要的结果返回给用户;如果不是,则服务器进程把块从IO读入到data buffer cache缓存下来,然后ondo块把该块做成镜像,然后从镜像中读取数据返回给用户。

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