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Control File Contents (67)

原创 IT综合 作者:tsinglee 时间:2007-10-17 15:37:24 0 删除 编辑

A control file contains information about the associated database that is required for
access by an instance, both at startup and during normal operation. Control file
information can be modified only by Oracle; no database administrator or user can
edit a control file.
Among other things, a control file contains information such as:
1. The database name
2. The timestamp of database creation
3. The names and locations of associated datafiles and redo log files
4. Tablespace information
5. Datafile offline ranges
6. The log history
7. Archived log information
8. Backup set and backup piece information
9. Backup datafile and redo log information
10. Datafile copy information
11. The current log sequence number
12. Checkpoint information
The database name and timestamp originate at database creation. The database name
is taken from either the name specified by the DB_NAME initialization parameter or the
name used in the CREATE DATABASE statement.
Each time that a datafile or a redo log file is added to, renamed in, or dropped from the
database, the control file is updated to reflect this physical structure change. These
changes are recorded so that:
■ Oracle can identify the datafiles and redo log files to open during database startup
■ Oracle can identify files that are required or available in case database recovery is
necessary
Therefore, if you make a change to the physical structure of your database (using
ALTER DATABASE statements), then you should immediately make a backup of your
control file.
Control files also record information about checkpoints. Every three seconds, the
checkpoint process (CKPT) records information in the control file about the checkpoint
position in the redo log. This information is used during database recovery to tell
Oracle that all redo entries recorded before this point in the redo log group are not
necessary for database recovery; they were already written to the datafiles.

控制文件的内容
包含如下内容 :数据库名称 , 数据库创建的时间戳 ,数据文件和重做日志文件的名称与位置 ,表空间信息 ,
数据文件脱机 , 日志历史 , 归档信息 , 备份集备份片信息 , 检查点信息等
数据名称和时间戳在数据库创建时生成 , 数据库名称有初始化参数db_name指定 , 或者create database时指定的名称
当数据文件或者重做日志文件有新增 , 改名 , 删除时 , 控制文件都会改变来映射新的物理结构 , 这样做可以使Oracle
确定数据库启动时需要的数据和重做文件
当使用 alter database来改变物理结构时 , 最好能备份控制文件
每三秒钟 , CKPT记录检查点的位置 , 此信息在数据库恢复时告诉Oracle此时间点之前的redo entries record都是不需要的 .
他们已经被写入了数据文件中

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