Oracle 实例和 Oracle 数据库
一般 Oracle 数据库(Oracle Database)可以分为两部分： (1) 实例(Instance) 实例是一个非固定的、基于内存的基本进程与内存结构。当服务器关闭后，实例也就不存在了。 (2) 数据库(Database) 数据库（Database）指的是固定的、基于磁盘的数据文件、控制文件、
一般 Oracle 数据库(Oracle Database)可以分为两部分：
(1) 实例(Instance)
实例是一个非固定的、基于内存的基本进程与内存结构。当服务器关闭后，实例也就不存在了。
(2) 数据库(Database)
数据库（Database）指的是固定的、基于磁盘的数据文件、控制文件、日志文件、参数文件和归档日志文件等。
一般情况下，Oracle数据库都是一个数据库对应一个实例。如下图所示。
数据服务器(Database server)一般指的是数据库各软件部件(如SQL PLUS，OEM，EXP/IMP等)和实例及数据库3个主要部分，是由安装在服务器上的所有软件(包括各种类型的文件)和启动成功后的实例组成的。
参考:《Oracle 11g 权威指南》(第二版) 谷长勇
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