Databases Reference
In-Depth Information
How It Works
Before Oracle can start up normally, it must be able to locate and open each of the control files identified by the
control_files
initialization parameter. The control files are identical copies of each other. If a multiplexed control
file becomes damaged, you can either modify the
control_files
initialization parameter to match the locations of
the remaining good control files or copy a good control file to the location of the damaged or missing control file.
If you have one good copy of a control file, you can use that to replace the damaged control files. This minimizes
the need to restore your control file from a backup.
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Multiplexing your control files minimizes the chance of failure with these critical files. We highly recommend that
you multiplex your control files and try to place each copy on separate devices governed by different controllers.
Tip
Re-creating the Control File
Problem
One of the following situations applies:
•
You've experienced a failure and lost all of your control files, and you belatedly realize that you
don't have a binary backup of the control file.
•
You want to change a database setting that can be modified only by re-creating the control file.
•
You are relocating a large number of data files and/or online redo log files, and you find it
easier to re-create the control file with the new names and locations (instead of manually
renaming the files).
Solution
Use the
alter database backup controlfile
command to create a SQL file that you can use to re-create your
control files. Here is the general syntax:
alter database backup controlfile to trace [as '<directory/filename>' [reuse]]
[resetlogs|noresetlogs];
For example, suppose you want to write a file named
recreate.sql
written to the
/orahome/oracle
directory:
SQL>alter database backup controlfile to trace
as '/orahome/oracle/recreate.sql' noresetlogs;
Database altered.
The prior command creates a file that contains a
create controlfile
SQL statement. Manually edit the newly
created file and take out the lines that you don't require (for example, there are a lot of comment lines initially in the
file). Here is some sample output for this example:
CREATE CONTROLFILE REUSE DATABASE "O12C" NORESETLOGS NOARCHIVELOG
MAXLOGFILES 16
MAXLOGMEMBERS 4
MAXDATAFILES 1024
