1 Introduction to the Oracle Database
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145
Overview of the Oracle Instance 1.1.7 Oracle实例概述
146 An Oracle database server consists of an Oracle
database and an Oracle instance. Every time a database
is started, a system global area (SGA) is allocated and
Oracle background processes are started. The
combination of the background processes and memory
buffers is called an Oracle instance.
一个Oracle数据库服务器包括Oracle数据库[此处特指
数据库物理文件]和Oracle实例。当数据库启动时,
将在内存中分配系统全局区(system global
area,SGA),并启动Oracle后台进程。上述内存区
和后台进程一起被称为Oracle实例(instance)。
147
Real Application Clusters: Multiple Instance Systems
1.1.7.1 Real Application Clusters: 多实例系统
148 Some hardware architectures (for example, shared disk
systems) enable multiple computers to share access to
data, software, or peripheral devices. Real Application
Clusters (RAC) takes advantage of such architecture by
running multiple instances that share a single physical
database. In most applications, RAC enables access to
a single database by users on multiple computers with
increased performance.
有的硬件体系结构(例如共享磁盘系统)可以让多
个计算机共享的使用数据、应用程序、或周边设
备。Real Application Clusters (实时应用集群,RAC)
通过运行多个实例同时访问一个物理数据库来发挥
这种体系结构的优势。在RAC体系结构下,可以提
高应用程序中多个用户访问同一数据库的性能。
149 An Oracle database server uses memory structures and
processes to manage and access the database. All
memory structures exist in the main memory of the
computers that constitute the database system.
Processes are jobs that work in the memory of these
computers.
Oracle数据库服务器使用其自身的内存结构和后台进
程来管理、访问数据库。所有内存结构都存在于数
据库系统所在计算机的主内存中。后台进程是工作
于计算机内存中的作业。
150 See Also:
Oracle Database Oracle Clusterware and
Oracle Real Application Clusters
Administration and Deployment Guide
另见:
Oracle
数据库集群组件及Oracle RAC 管理
与部署指南
151
Instance Memory Structures
1.1.7.2 实例内存结构
152 Oracle creates and uses memory structures to complete
several jobs. For example, memory stores program
code being run and data shared among users. Two
basic memory structures are associated with Oracle:
the system global area and the program global area.
The following subsections explain each in detail.
Oracle创建并利用内存结构来完成各项工作。例如,
在内存中存储需要运行的程序代码和用户使用的数
据。和Oracle有关的两个基本内存结构是系统全局区
(system global area,SGA)和程序全局区
(program global area,PGA)。以下各小节将做进
一步解释。
153
System Global Area
1.1.7.3 系统全局区
154 The System Global Area (SGA) is a shared memory
region that contains data and control information for
one Oracle instance. Oracle allocates the SGA when an
instance starts and deallocates it when the instance
shuts down. Each instance has its own SGA.
系统全局区(System Global Area,SGA)是包含了
一个Oracle实例所拥有的数据及控制信息的共享内存
区域。Oracle在实例启动时分配SGA空间,并在实例
关闭时回收。每个实例都有自己的SGA。
155 Users currently connected to an Oracle database share
the data in the SGA. For optimal performance, the
entire SGA should be as large as possible (while still
fitting in real memory) to store as much data in
memory as possible and to minimize disk I/O.
连接到Oracle数据库中的用户可以共享SGA中的数
据。为了优化性能,应该使SGA尽可能的大(还要
依据实际可用内存情况而定),以便在内存中尽可
能多的存储数据,使磁盘I/O最小化。
156 The information stored in the SGA is divided into
several types of memory structures, including the
database buffers, redo log buffer, and the shared pool.
SGA的内容可以被分为以下几类内存结构,包括数
据库缓冲区,重做日志缓冲区,和共享池。