Oracle Database Administration chapter-4

Managing Control Files

Every Oracle Database has a control file, which is a small binary file that records the physical structure of the database. The control file includes:

·         The database name

·         Names and locations of associated datafiles and redo log files

·         The timestamp of the database creation

·         The current log sequence number

·         Checkpoint information

It is strongly recommended that you multiplex control files  i.e. Have at least two control files one in one hard disk and another one located in another disk, in a database.  In this way if control file becomes corrupt in one disk the another copy will be available and you don’t have to do recovery of control file.

You can  multiplex control file at the time of creating a database and later on also. If you have not multiplexed control file at the time of creating a database you can do it now by following given procedure.

Multiplexing Control File

Steps:

      1.      Shutdown the Database.

SQL>SHUTDOWN IMMEDIATE;

    2.      Copy the control file from old location to new location using operating system command. For example.

$cp /u01/oracle/ica/control.ora  /u02/oracle/ica/control.ora

    3.      Now open the parameter file and specify the new location like this

CONTROL_FILES=/u01/oracle/ica/control.ora

Change it to

CONTROL_FILES=/u01/oracle/ica/control.ora,/u02/oracle/ica/control.ora

    4.      Start the Database

Now Oracle will start updating both the control files and, if one control file is lost you can copy  it from another location.

Changing the Name of a Database

If you ever want to change the name of database or want to change the setting of MAXDATAFILES, MAXLOGFILES, MAXLOGMEMBERS then you have to create a new control file.

Creating A New Control File

Follow the given steps to create a new controlfile

Steps

1.      First generate the create controlfile statement

SQL>alter database backup controlfile to trace;

After giving this statement oracle will write the CREATE CONTROLFILE statement in a trace file. The trace file will be randomly named something like ORA23212.TRC and it is created in USER_DUMP_DEST directory.

2.      Go to the USER_DUMP_DEST directory and open the latest trace file in text editor. This file will contain the CREATE CONTROLFILE statement. It will have two sets of statement one with RESETLOGS and another without RESETLOGS. Since we are changing the name of the Database we have to use RESETLOGS option of CREATE CONTROLFILE statement. Now copy and paste the statement in a file. Let it be c.sql

3.      Now open the c.sql file in text editor and set the database name from ica to prod shown in an example below

CREATE CONTROLFILE

   SET DATABASE prod   

   LOGFILE GROUP 1 ('/u01/oracle/ica/redo01_01.log',

                    '/u01/oracle/ica/redo01_02.log'),

           GROUP 2 ('/u01/oracle/ica/redo02_01.log',

                    '/u01/oracle/ica/redo02_02.log'),

           GROUP 3 ('/u01/oracle/ica/redo03_01.log',

                    '/u01/oracle/ica/redo03_02.log')

   RESETLOGS

   DATAFILE '/u01/oracle/ica/system01.dbf' SIZE 3M,

            '/u01/oracle/ica/rbs01.dbs' SIZE 5M,

            '/u01/oracle/ica/users01.dbs' SIZE 5M,

            '/u01/oracle/ica/temp01.dbs' SIZE 5M

   MAXLOGFILES 50

   MAXLOGMEMBERS 3

   MAXLOGHISTORY 400

   MAXDATAFILES 200

   MAXINSTANCES 6

   ARCHIVELOG;

4.      Start and do not mount the database.

SQL>STARTUP NOMOUNT;

5.      Now execute c.sql script

SQL> @/u01/oracle/c.sql

6.      Now open the database with RESETLOGS

SQL>ALTER DATABASE OPEN RESETLOGS;

Cloning an Oracle Database.

You have a Production database running in one server. The company management wants to develop some new modules and they have hired some programmers to do that. Now these programmers require access to the Production database and they want to make changes to it. You as a DBA can’t give direct access to Production database so you want to create a copy of this database on another server and wants to give developers access to it.

Let us see an example of cloning a database

We have a database running the production server with the following files

PARAMETER FILE located in /u01/oracle/ica/initica.ora

CONTROL FILES=/u01/oracle/ica/control.ora
BACKGROUND_DUMP_DEST=/u01/oracle/ica/bdump
USER_DUMP_DEST=/u01/oracle/ica/udump
CORE_DUMP_DEST=/u01/oracle/ica/cdump
LOG_ARCHIVE_DEST_1=”location=/u01/oracle/ica/arc1”

DATAFILES =

            /u01/oracle/ica/sys.dbf
            /u01/oracle/ica/usr.dbf
            /u01/oracle/ica/rbs.dbf
            /u01/oracle/ica/tmp.dbf
            /u01/oracle/ica/sysaux.dbf

LOGFILE=

            /u01/oracle/ica/log1.ora
            /u01/oracle/ica/log2.ora

Now you want to copy this database to SERVER  2 and in SERVER 2 you don’t have /u01 filesystem. In SERVER 2 you have /d01 filesystem.

To Clone this Database on SERVER 2 do the following.

Steps :-

1.      In SERVER 2 install the same version of o/s and same version Oracle as in SERVER 1.

2.      In SERVER 1 generate CREATE CONTROLFILE statement by typing the following command

SQL>alter database backup controlfile to trace;

Now, go to the USER_DUMP_DEST directory and open the latest trace file. This file will contain steps and as well as CREATE CONTROLFILE statement. Copy the CREATE CONTROLFILE statement and paste in a file. Let the filename be cr.sql

The CREATE CONTROLFILE Statement will look like this.

CREATE CONTROLFILE

   SET DATABASE prod   

   LOGFILE GROUP 1 ('/u01/oracle/ica/log1.ora'

           GROUP 2 ('/u01/oracle/ica/log2.ora'

  DATAFILE '/u01/oracle/ica/sys.dbf' SIZE 300M,

            '/u01/oracle/ica/rbs.dbf' SIZE 50M,

            '/u01/oracle/ica/usr.dbf' SIZE 50M,

            '/u01/oracle/ica/tmp.dbf' SIZE 50M,

                      ‘/u01/oracle/ica/sysaux.dbf’ size 100M;

   MAXLOGFILES 50

   MAXLOGMEMBERS 3

   MAXLOGHISTORY 400

   MAXDATAFILES 200

   MAXINSTANCES 6

   ARCHIVELOG;

3.      In SERVER 2 create the following directories

$cd /d01/oracle

$mkdir ica

$mkdir arc1

$cd ica

$mkdir bdump udump cdump

Shutdown the database on SERVER 1 and transfer all datafiles, logfiles and  control file to SERVER 2 in /d01/oracle/ica directory.

Copy parameter file to SERVER 2 in /d01/oracle/dbs directory and copy all archive log files to SERVER 2 in /d01/oracle/ica/arc1 directory. Copy the cr.sql script file to /d01/oracle/ica directory.

4.      Open the parameter file SERVER 2 and change the following parameters

CONTROL FILES=//d01/oracle/ica/control.ora
BACKGROUND_DUMP_DEST=//d01/oracle/ica/bdump
USER_DUMP_DEST=//d01/oracle/ica/udump
CORE_DUMP_DEST=//d01/oracle/ica/cdump
LOG_ARCHIVE_DEST_1=”location=//d01/oracle/ica/arc1”

5.      Now, open the cr.sql file in text editor and change the locations like this

CREATE CONTROLFILE

   SET DATABASE prod   

   LOGFILE GROUP 1 ('//d01/oracle/ica/log1.ora'

           GROUP 2 ('//d01/oracle/ica/log2.ora'

  DATAFILE '//d01/oracle/ica/sys.dbf' SIZE 300M,

            '//d01/oracle/ica/rbs.dbf' SIZE 50M,

            '//d01/oracle/ica/usr.dbf' SIZE 50M,

            '//d01/oracle/ica/tmp.dbf' SIZE 50M,

                      ‘//d01/oracle/ica/sysaux.dbf’ size 100M;

   MAXLOGFILES 50

   MAXLOGMEMBERS 3

   MAXLOGHISTORY 400

   MAXDATAFILES 200

   MAXINSTANCES 6

   ARCHIVELOG;

In SERVER 2 export ORACLE_SID environment variable and start the instance

$export ORACLE_SID=ica

$sqlplus

Enter User:/ as sysdba

SQL> startup nomount;

6.      Run cr.sql script to create the controlfile

SQL>@/d01/oracle/ica/cr.sql

7.      Open the database

SQL>alter database open;