Control Files

• The Control file is a small binary file that necessary for the database to start and operate successfully.
• Each Control file is associated with only one Oracle database.
• Control file is required at Mount stage during database startup and is required to operate the database
• A control file is updated continuously by the Oracle server during the 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 administartor or end user can edit the control file.
• If for some reason the control file is not accessible, the database does not function properly.
• If all copies of a database control files are lost, the database must be recovered before it can be opened.

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The contents of Control File:

• Database Name and Identifier
• Names and Locations of associated data files and online redo log files
• Time stamp of database creation
• The current log sequence number
• Check point information
• Tablespace Information
• Redo log archive information
• Location and status of Backups are recorded by the RMAN utility.

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Sizing the Control File:

• Keywords specified during the creation of the database affect the size of the control file.
• The size of the control file is influenced by the following keywords in the CREATE DATABASE or CREATE CONTROLFILE commands:

1. MAXLOGFILES
2. MAXLOGMEMBERS
3. MAXLOGHISTORY
4. MAXDATAFILES
5. MAXINSTANCES

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Multiplexing the Control File

I-Using SPFILE

Step 1: using ALTER SYSTEM SET command alter the SPFILE to include the list of control files to be used: main control file, multiplexed copies

Example:

SQL>ALTER SYSTEM SET control_files=

'/u01/oracle/product/10.2/DB1/ctrl01.ctl',

'/u02/oracle/product/10.2/DB1/ctrl02.ctl' SCOPE= SPFILE;

Step 2: Shutdown the database

Example:

SQL>shutown immediate

Step 3: Create additional control files

Example:

SQL>!cp /u01/oracle/product/10.2/DB1/ctrl01.ctl

/u02/oracle/product/10.2/DB1/ctrl02.ctl

(SQL>!cp )

Step 4: Startup the database

Example:

SQL>STARTUP

II-Using PFILE

Step 1: Shutdown the Database

Step 2: Create additional control files using OS copy command.

Step 3: Add new control file names to PFILE (Initialization Parameter file)

Step 4: Startup the database

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Control File Information

• V$CONTROLFILE : List the name and status of the control files.
• V$PARAMETER :List the status and location of all parameters
• V$CONTROLFILE_RECORD_SECTION: Provides the information about the control file record section
• SHOW PARAMETER CONTROL_FILES : Lists the name, status, and location of the control files.