Control file and its functions in Oracle.

Control file and its functions in Oracle

This article answers the following queries :
•         What is the control file in oracle?
•         What are the functions of control file in oracle?
•         What are the control file contents ?
•         Can database function properly without control file?
•         Can we edit control file
•         Who can modify control file?
•         At what time control file will be created?

What is control file in Oracle and what are its functions ?
Control file is a small binary file which is necessary for the database to start and operate successfully.

What are the functions of control file ?
Each control file is associated with only one database.  Oracle continuously updates control file during database use so this file must be available for writing whenever the database is in the open state.  Control file will be created at the same time of database creation.
Whenever a datafile or a redolog file is added to, dropped or renamed in the database, the control file is updated to reflect the physical structural change.
These changes are recorded in control file which facilitates:
>   Oracle to identify the files that are required or available in case database recovery is needed
>   Oracle to identify the datafiles and redolog files to open during database startup.

Can database function properly without control file?
No. Database cannot function properly if the control file is not available.

Can we edit control file? Who can modify control file?
Please note control file cannot be edited by database administrator or by any user. Control file information can only be modified by Oracle.

Contents of control files :
> Control file contains information such as
>   Database name
>   Timestamp of database creation
>   Tablespace information
>   The log history
>   Archive log information
>   Current log sequence number
>   Checkpoint information
>   Names and locations of associated datafiles and redolog files
>   Datafile copy information
>   Datafile offline ranges
>   Backup set and backup related information
>   Backup datafile and redolog information