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oracle core 概述

時間：2014-04-28 01:14:08 阅读：621 評論：0 收藏：0 [點我收藏+]

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oracle數據庫系统的架构及其复杂，其提供的特性也非常的多。作为一种关系型數據庫，oracle提供的基本特性：

transaction
concurrency
read consistent

而支撐這些特性的必不或缺的組件組成了Oracle Core。

如下面的縮略圖所示

：

這個oracle系統的架構圖涵蓋了oracle最基本也是最爲重要的組件，理解了這些組件的協作關系，基本上就掌握了oracle的處理機制。
对于oracle core来说，这些已足够。

　　

1，文件：

图中描述了两种文件，Data files保存了真实的数据，redo log files连续的保存了系统对data files更改的记录。 data file的访问属于随机访问，这里牵涉到block size，tablespace，extent，segment等逻辑结构的概念，略..... redo log file属于顺序I/O，分为两种online redo log file，archived redo log files。

2，內存：

SGA作为oracle數據庫实例的共享内存部分，包括多种结构： data buffer：存放数据块的拷贝 log buffer：即将写入redo log file的重做日志 library cache：执行的sql或者plsql信息

3，scn：

协调整个oracle系统活动的一个时钟，称为System Change number。当发生commit的时候，scn号会递增，但这仅仅是scn号递增的一种情况，所以system commit number这个名词并不能完全描述scn。

4，後台進程：

dbwr：拷贝data cache中的数据到data files中。 lgwr：拷贝redo buffer中的重做到redo log files中。

5，用戶進程：

dedicated server：为每一个用户进程分配一个服务器进程 shared server：处理轻量级任务。　　下面的这个系列就来介绍一下这些组件是如何来有效的进行协作。

oracle core 概述,码迷,mamicode.com

oracle core 概述

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原文地址：http://www.cnblogs.com/xpchild/p/3695115.html

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