Oracle物理结构概述
数据文件每一个Oracle数据库都有一个或多个物理的数据文件,数据库信息(结构,数据)都保存在这些数据文件中,并且这些文件也只Oracl
数据文件
每一个Oracle数据库都有一个或多个物理的数据文件,数据库信息(结构,数据)都保存在这些数据文件中,并且这些文件也只Oracle才能够解释与管理这些存储.Oracle数据文件具有以下一些特性:
1.一个数据文件仅仅关联一个数据库,数据文件与数据库之间对应关系是一对一关系,当然反过数据库与数据文件是一对多关系.
2.数据文件可以自动扩展,当数据存储需要更多存储空间时候,就是存储数据的数据随存储数据量增大,数据文件也可以自动增长,以满足数据存储需要.
3.一个或多个数据文件组成一个逻辑单元,称之为表空间.数据文件与表空间之间对应关系也是一对一关系,当然反过表空间与数据文件对应关系是一对多的关系.
存储在数据文件中的是可以读,当然这些数据是保存在Oracle数据库实例中特定的内存区域中,如果一个用户要读取数据库中一个表,这个用户是不能直接读取物理磁盘上的数据文件的,首先Oracle接受这个请求后,从造当位置(物理磁盘)上读取相应的数据到内存中,这个时候用户才可以看见数据.Oracle软件是解释Oracle存储与管理数据的.如果这个时候我们修改数据,这些数据是不会立即写到磁盘中的.要到特定时候才会写磁盘.频繁立即写会引I/O性能下降.
Oracle会在特定时候完成这数据写工作.
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