Creating Co ntrol Files

This section describes ways to create control files, and contains the following topics:

Creating Initial Control Files
Creating Additional Copies, Renaming, and Relocating Control Files
Creating New Control Files

Creating Initial Control Files

The initial control files of an Oracle Database are created when you issue the CREATE DATABASE statement. The names of the control files are specified by the CONTROL_FILES parameter in the initialization parameter file used during database creation. The filenames specified in CONTROL_FILES should be fully specified and are operating system specific. The following is an example of a CONTROL_FILES initialization parameter:

CONTROL_FILES = (/u01/oracle/prod/control01.ctl,
                 /u02/oracle/prod/control02.ctl, 
                 /u03/oracle/prod/control03.ctl)

If files with the specified names currently exist at the time of database creation, you must specify the CONTROLFILE REUSE clause in the CREATE DATABASE statement, or else an error occurs. Also, if the size of the old control file differs from the SIZE parameter of the new one, you cannot use the REUSE clause.

The size of the control file changes between some releases of Oracle Database, as well as when the number of files specified in the control file changes. Configuration parameters such as MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, MAXDATAFILES, and MAXINSTANCES affect control file size.

You can subsequently change the value of the CONTROL_FILES initialization parameter to add more control files or to change the names or locations of existing control files.

Creating Additional Copies, Renaming, and Relocating Control Files

You can create an additional control file copy for multiplexing by copying an existing control file to a new location and adding the file name to the list of control files. Similarly, you rename an existing control file by copying the file to its new name or location, and changing the file name in the control file list. In both cases, to guarantee that control files do not change during the procedure, shut down the database before copying the control file.

To add a multiplexed copy of the current control file or to rename a control file:

Shut down the database.
Copy an existing control file to a new location, using operating system commands.
Edit the CONTROL_FILES parameter in the database initialization parameter file to add the new control file name, or to change the existing control filename.
Restart the database.

Creating New Control Files

This section discusses when and how to create new control files.

When to Create New Control Files

It is necessary for you to create new control files in the following situations:

All control files for the database have been permanently damaged and you do not have a control file backup.
You want to change the database name.

For example, you would change a database name if it conflicted with another database name in a distributed environment.

Note:
You can change the database name and DBID (internal database identifier) using the DBNEWID utility. See Oracle Database Utilities for information about using this utility.
The compatibility level is set to a value that is earlier than 10.2.0, and you must make a change to an area of database configuration that relates to any of the following parameters from the CREATE DATABASE or CREATE CONTROLFILE commands: MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, and MAXINSTANCES. If compatibility is 10.2.0 or later, you do not have to create new control files when you make such a change; the control files automatically expand, if necessary, to accommodate the new configuration information.

For example, assume that when you created the database or recreated the control files, you set MAXLOGFILES to 3. Suppose that now you want to add a fourth redo log file group to the database with the ALTER DATABASE command. If compatibility is set to 10.2.0 or later, you can do so and the controlfiles automatically expand to accommodate the new logfile information. However, with compatibility set earlier than 10.2.0, your ALTER DATABASE command would generate an error, and you would have to first create new control files.

For information on compatibility level, see "About The COMPATIBLE Initialization Parameter".

The CREATE CONTROLFILE Statement

You can create a new control file for a database using the CREATE CONTROLFILE statement. The following statement creates a new control file for the prod database (a database that formerly used a different database name):

CREATE CONTROLFILE
   SET DATABASE prod
   LOGFILE GROUP 1 ('/u01/oracle/prod/redo01_01.log', 
                    '/u01/oracle/prod/redo01_02.log'),
           GROUP 2 ('/u01/oracle/prod/redo02_01.log', 
                    '/u01/oracle/prod/redo02_02.log'),
           GROUP 3 ('/u01/oracle/prod/redo03_01.log', 
                    '/u01/oracle/prod/redo03_02.log') 
   RESETLOGS
   DATAFILE '/u01/oracle/prod/system01.dbf' SIZE 3M,
            '/u01/oracle/prod/rbs01.dbs' SIZE 5M,
            '/u01/oracle/prod/users01.dbs' SIZE 5M,
            '/u01/oracle/prod/temp01.dbs' SIZE 5M
   MAXLOGFILES 50
   MAXLOGMEMBERS 3
   MAXLOGHISTORY 400
   MAXDATAFILES 200
   MAXINSTANCES 6
   ARCHIVELOG;

Cautions:

The CREATE CONTROLFILE statement can potentially damage specified datafiles and redo log files. Omitting a filename can cause loss of the data in that file, or loss of access to the entire database. Use caution when issuing this statement and be sure to follow the instructions in "Steps for Creating New Control Files".
If the database had forced logging enabled before creating the new control file, and you want it to continue to be enabled, then you must specify the FORCE LOGGING clause in the CREATE CONTROLFILE statement. See "Specifying FORCE LOGGING Mode".

Steps for Creating New Control Files

Complete the following steps to create a new control file.

Make a list of all datafiles and redo log files of the database.

If you follow recommendations for control file backups as discussed in "Backing Up Control Files" , you will already have a list of datafiles and redo log files that reflect the current structure of the database. However, if you have no such list, executing the following statements will produce one.
```
SELECT MEMBER FROM V$LOGFILE;
SELECT NAME FROM V$DATAFILE; 
SELECT VALUE FROM V$PARAMETER WHERE NAME = 'control_files';
```
If you have no such lists and your control file has been damaged so that the database cannot be opened, try to locate all of the datafiles and redo log files that constitute the database. Any files not specified in step 5 are not recoverable once a new control file has been created. Moreover, if you omit any of the files that make up the SYSTEM tablespace, you might not be able to recover the database.
Shut down the database.

If the database is open, shut down the database normally if possible. Use the IMMEDIATE or ABORT clauses only as a last resort.
Back up all datafiles and redo log files of the database.
Start up a new instance, but do not mount or open the database:
```
STARTUP NOMOUNT
```
Create a new control file for the database using the CREATE CONTROLFILE statement.

When creating a new control file, specify the RESETLOGS clause if you have lost any redo log groups in addition to control files. In this case, you will need to recover from the loss of the redo logs (step 8). You must specify the RESETLOGS clause if you have renamed the database. Otherwise, select the NORESETLOGS clause.
Store a backup of the new control file on an offline storage device. See "Backing Up Control Files" for instructions for creating a backup.
Edit the CONTROL_FILES initialization parameter for the database to indicate all of the control files now part of your database as created in step 5 (not including the backup control file). If you are renaming the database, edit the DB_NAME parameter in your instance parameter file to specify the new name.
Recover the database if necessary. If you are not recovering the database, skip to step 9.

If you are creating the control file as part of recovery, recover the database. If the new control file was created using the NORESETLOGS clause (step 5), you can recover the database with complete, closed database recovery.

If the new control file was created using the RESETLOGS clause, you must specify USING BACKUP CONTROL FILE. If you have lost online or archived redo logs or datafiles, use the procedures for recovering those files.

See Also:
Oracle Database Backup and Recovery User's Guide for information about recovering your database and methods of recovering a lost control file
Open the database using one of the following methods:
- If you did not perform recovery, or you performed complete, closed database recovery in step 8, open the database normally.
```
ALTER DATABASE OPEN; 
```
- If you specified RESETLOGS when creating the control file, use the ALTER DATABASE statement, indicating RESETLOGS.
```
ALTER DATABASE OPEN RESETLOGS;
```

The database is now open and available for use.

Creating Control Files