数据库启动之MOUNT

How a Database Is Mounted

The instance mounts a database to associate the database with this instance. To mount the database, the instance obtains the names of the database control files specified in the CONTROL_FILES initialization parameter and opens the files. Oracle Database reads the control files to find the names of the data files and the online redo log files that it will attempt to access when opening the database.

In a mounted database, the database is closed and accessible only to database administrators. Administrators can keep the database closed while completing specific maintenance operations. However, the database is not available for normal operations.

If Oracle Database allows multiple instances to mount the same database concurrently, then the CLUSTER_DATABASE initialization parameter setting can make the database available to multiple instances. Database behavior depends on the setting:

• If CLUSTER_DATABASE is false (default) for the first instance that mounts a database, then only this instance can mount the database.

• If CLUSTER_DATABASE is true for the first instance, then other instances can mount the database if their CLUSTER_DATABASE parameter settings are set totrue. The number of instances that can mount the database is subject to a predetermined maximum specified when creating the database.

See Also:

• Oracle Database Administrator's Guide to learn how to mount a database

• Oracle Real Application Clusters Administration and Deployment Guide for more information about the use of multiple instances with a single database

实例挂载
mount状态下实例与数据库发生关联。挂载数据库，实例从初始化变量CONTROL_FILES中获取数据库控制文件并打开之。数据库读取控制文件，找到数据文件和联机重做日志文件的名字，它会尝试打开数据库时访问。
mount状态情况下，数据库是关闭的，并且只有数据库管理员可以访问。完成特定的维护操作的同时，管理员可以保持数据库关闭。然而，一般的数据库操作还是不允许的。
如果数据库允许同时挂载多个实例，那么可以用初始化变量CLUSTER_DATABASE设置；依据下列设置：
 如果第一个实例挂载数据库时初始化变量CLUSTER_DATABASE 设置为FALSE（默认设置），那么仅只有该实例可以挂载到数据库上
 如果第一个实例挂载数据库时初始化变量CLUSTER_DATABASE 设置为TRUE，那么其他的实例的初始化变量CLUSTER_DATABASE如果也设置为TRUE,这些实例也可以挂载到该数据库上。数据库能够被挂在的实例数量是根据数据库创建的时候预定义的最大数量。