How and When to create a control file......?

Q. When to create control files ?
A. Create controlfiles when
1. You have lost all your control files.
2. When you want to rename a database name (db_name)

Q. How to create control files.
You need a create controlfile script for recreating control files.

SQL*Plus: Release 9.2.0.2.0 - Production on Fri Feb 28 17:04:00 2003
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.

Enter user-name: sys as sysdbaEnter password:Connected to:Oracle9i Enterprise Edition Release 9.2.0.2.1 - ProductionWith the Partitioning, Oracle Label Security, OLAP and Oracle Data Mining optionsJServer Release 9.2.0.2.0 -
Production

SQL> alter database backup controlfile to trace;
Database altered.
SQL>This will create a trace file in the udump directory.
Im my case it wasE:\oracle\admin\ORCL\udump\orcl_ora_2052.trc
Edit the file to point the path of the datafiles and redologfiles.

CREATE CONTROLFILE REUSE DATABASE "ORCL" RESETLOGS ARCHIVELOGMAXLOGFILES 5MAXLOGMEMBERS 3MAXDATAFILES 14MAXINSTANCES 1MAXLOGHISTORY 226LOGFILEGROUP 1 'E:\ORACLE\ORADATA\ORCL\REDO01.LOG' SIZE 100M,GROUP 2 'E:\ORACLE\ORADATA\ORCL\REDO02.LOG' SIZE 100M,GROUP 3 'E:\ORACLE\ORADATA\ORCL\REDO03.LOG' SIZE 100MDATAFILE'E:\ORACLE\ORADATA\ORCL\SYSTEM01.DBF','E:\ORACLE\ORADATA\ORCL\UNDOTBS01.DBF','E:\ORACLE\ORADATA\ORCL\EXAMPLE01.DBF','E:\ORACLE\ORADATA\ORCL\INDX01.DBF','E:\ORACLE\ORADATA\ORCL\TOOLS01.DBF','E:\ORACLE\ORADATA\ORCL\USERS01.DBF','E:\ORACLE\ORADATA\ORCL\OEM_REPOSITORY.DBF','E:\ORACLE\ORADATA\ORCL\CWMLITE01.DBF','E:\ORACLE\ORADATA\ORCL\DRSYS01.DBF','E:\ORACLE\ORADATA\ORCL\ODM01.DBF','E:\ORACLE\ORADATA\ORCL\XDB01.DBF','E:\ORACLE\ORADATA\ORCL\USERS02.DBF','E:\ORACLE\ORADATA\ORCL\USERS03.DBF','E:\ORACLE\ORADATA\ORCL\USERS04.DBF'CHARACTER SET WE8MSWIN1252;ALTER DATABASE OPEN RESETLOGS;and rename it to ctl.sqlThen startup the database in nomount mode and run the ctl.sql file as sys as sysdba userSQL*Plus: Release 9.2.0.2.0 - Production on Fri Feb 28 17:25:14 2003Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.Enter user-name: sys as sysdbaEnter password:Connected to an idle instance.SQL> startup nomountORACLE instance started.Total System Global Area 80812648 bytesFixed Size 453224 bytesVariable Size 54525952 bytesDatabase Buffers 25165824 bytesRedo Buffers 667648 bytesS
QL> @E:\oracle\admin\ORCL\udump\ctl.sql
Control file created.
Database altered.
SQL> select status from v$instance;
STATUS-----------------------------------OPEN
SQL> select name from v$controlfile;
NAME--------------------------------------------------------E:\ORACLE\ORADATA\ORCL\CONTROL01.
CTLE:\ORACLE\ORADATA\ORCL\CONTROL02.
CTLE:\ORACLE\ORADATA\ORCL\CONTROL03.
CTLTo rename the database change reuse to set in the create control file script as shown belowCREATE CONTROLFILE SET DATABASE "ORCL" RESETLOGS ARCHIVELOGMAXLOGFILES 5MAXLOGMEMBERS 3MAXDATAFILES 14MAXINSTANCES 1MAXLOGHISTORY 226LOGFILEGROUP 1
'E:\ORACLE\ORADATA\ORCL\REDO01.LOG' SIZE 100M,GROUP 2 'E:\ORACLE\ORADATA\ORCL\REDO02.LOG' SIZE 100M,GROUP 3 'E:\ORACLE\ORADATA\ORCL\REDO03.LOG' SIZE 100MDATAFILE'
E:\ORACLE\ORADATA\ORCL\SYSTEM01.DBF','
E:\ORACLE\ORADATA\ORCL\UNDOTBS01.DBF','
E:\ORACLE\ORADATA\ORCL\EXAMPLE01.DBF','
E:\ORACLE\ORADATA\ORCL\INDX01.DBF','
E:\ORACLE\ORADATA\ORCL\TOOLS01.DBF','
E:\ORACLE\ORADATA\ORCL\USERS01.DBF','
E:\ORACLE\ORADATA\ORCL\OEM_REPOSITORY.DBF','
E:\ORACLE\ORADATA\ORCL\CWMLITE01.DBF','
E:\ORACLE\ORADATA\ORCL\DRSYS01.DBF','
E:\ORACLE\ORADATA\ORCL\ODM01.DBF','
E:\ORACLE\ORADATA\ORCL\XDB01.DBF','
E:\ORACLE\ORADATA\ORCL\USERS02.DBF','
E:\ORACLE\ORADATA\ORCL\USERS03.DBF','
E:\ORACLE\ORADATA\ORCL\USERS04.DBF'
CHARACTER SET WE8MSWIN1252;
ALTER DATABASE OPEN RESETLOGS;