Introductionof oracle control file

 

Introductionof oracle control file

 

1. It is created when database is created,It can be re-created. 

2. The control file is a small binary file necessary for the database to start and operate successfully. If for some reason the control file is not accessible, the database does not function properly.

3. Every Oracle database has a control file. Each control file is associated with only one Oracle database.

4. A control file contains entries that specify the physical structure of the database. The contents of the control file include the following:

(1)The database name to which the control file belongs. A control file can belong to only one database.
(2)The database creation time stamp.
(3)The name, location, and online/offline status information of the datafiles.
(4)The name and location of the redo log files.
(5)Redo log archive information.
(6)Tablespace names.
(7)The current log sequence number , which is a unique identifier that is incremented and recorded when an online redo log file is switched.
(8)The most recent checkpoint information.
(9)The beginning and ending of undo segments.
(10)Recovery Manager’s backup information.( Recovery Manager (RMAN) is the Oracle utility you use to back up and recover databases.)

5. Like the redo log, Oracle lets the control file be multiplexed for protection of the control file, can be multiplexed up to eight times.
6. Before a database is opened, the control file is read to determine if the database is in a valid state to use.

7. A control file is updated continuously by the Oracle server during database use, so it must be available for writing whenever the database is open. The information in the control file can be modified only by the Oracle server; no database administrator or end user can edit the control file.

8. If all copies of a database’s control files are lost, the database must be recovered before it can be opened. At least one control file is required, but control files can be multiplexed up to eight times.