Sql Server系统数据库有什么作用
Master Master数据库保存有放在SQLSERVER实体上的所有数据库，它还是将引擎固定起来的粘合剂。由于如果不使用主数据库，SQLSERVER就不能启动，所以你必须要小心地管理好这个数据库。因此，对这个数据库进行常规备份是十分必要的。 这个数据库包括了诸如系统
Master
Master数据库保存有放在SQLSERVER实体上的所有数据库，它还是将引擎固定起来的粘合剂。由于如果不使用主数据库，SQLSERVER就不能启动，所以你必须要小心地管理好这个数据库。因此，对这个数据库进行常规备份是十分必要的。
这个数据库包括了诸如系统登录、配置设置、已连接的SERVER等信息，以及用于该实体的其他系统和用户数据库的一般信息。主数据库还存有扩展存储过程，它能够访问外部进程，从而让你能够与磁盘子系统和系统API调用等特性交互。这些过程一般都用像C++这样的现代编程语言。
如果不幸碰到系统崩溃而必须恢复主数据库的情况，你可以参看MCSE/MCDBA Steven Warren在TechRepublic上发表的文章。这篇文章讲得十分透彻，它解释了恢复这一重要数据库所需要的一些特殊步骤。
Model
Model是一个用来在实体上创建新用户数据库的模版数据库。你可以把任何存储过程、视图、用户等放在模型数据库里，这样在创建新数据库的时候，新数据库就会包含你放在模型数据库里的所有对象了。
Tempdb
正如其名字所提示的，tempdb存有临时对象，例如全局和本地临时表格和存储过程。
这个数据库在SQLSERVER每次重启的时候都会被重新创建，而其中包含的对象是依据模型数据库里定义的对象被创建的。除了这些对象，tempdb还存有其他对象，例如表格变量、来自表格值函数的结果集，以及临时表格变量。由于tempdb会保留SQLSERVER实体上所有数据库的这些对象类型，所以对数据库进行优化配置是非常重要的。
在SQL Server 2005里，tempdb数据库还有一项额外的任务;它还被用作一些特性的版本库，例如新的快照隔离层和在线索引操作等。关于新的隔离层的简要说明，请参考我关于SQL Server 2005高级特性的文章。
Distribution
当你的SQLSERVER实体被配置为复制分发SERVER时，这个数据库就会被添加到你的系统里。在默认情况下，数据库的名字就是distribution，但是你可以更改它的名字。这个数据库用来保存历史和快照、合并和事务复制等的元数据。
Msdb
Msdb数据库用来保存于数据库备份、SQL Agent信息、DTS程序包、SQLSERVER任务等信息，以及诸如日志转移这样的复制信息。
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