Lesson 1

Oracle uses a control file to keep track of the current state of a database. You, the database administrator (DBA), use initialization parameters to control many aspects of how a database operates. This module gives you the information that you need to manage both the control file and the initialization parameters. By the end of this module, you will know how to:

1. Explain the importance of multiplexing the control files
2. Add new control files to a database
3. Move an existing control file
4. Remove a control file from a database
5. Back up your control file
6. View current database parameter settings
7. Change parameter settings while the database is open

The first part of this module concentrates on the skills that you need to manage the control file. The last part of the module covers database parameter settings.

In Oracle Database 19c, multiplexing control files is a critical best practice for database reliability and fault tolerance. It involves maintaining multiple identical copies of control files to protect against corruption or loss.
Here's a detailed explanation:
What is a Control File?
A control file is a small binary file that maintains critical metadata about the database, including:

• Database name and identifier (DBID)
• Data file names and locations
• Online redo log file locations
• Checkpoint information
• Archive log history
• Information about backup and recovery

If a control file is damaged or lost, the database cannot function normally, resulting in immediate downtime or data loss until recovery occurs. ## Why Multiplex Control Files in Oracle 19c? Multiplexing control files addresses these potential risks:
How to Multiplex Control Files in Oracle 19c
Step-by-Step Procedure:
1. Check existing control files:

-- List current control file locations
SELECT name FROM v$controlfile;

Output example:

+--------------------------------------------+
| NAME                                       |
+--------------------------------------------+
| /u01/app/oracle/oradata/ORCLCDB/control01.ctl |
| /u01/app/oracle/oradata/ORCLCDB/control02.ctl |
+--------------------------------------------+

2. Add a new control file copy:
- Shutdown the database gracefully:

SHUTDOWN IMMEDIATE;

- Copy an existing control file to a new location (done at OS level):

cp /u01/app/oracle/oradata/ORCLCDB/control01.ctl /u02/app/oracle/oradata/ORCLCDB/control03.ctl

- Update the initialization parameter (`CONTROL_FILES`) to include the new control file in your `init.ora` or `spfile`:

ALTER SYSTEM SET CONTROL_FILES =
 '/u01/app/oracle/oradata/ORCLCDB/control01.ctl',
 '/u01/app/oracle/oradata/ORCLCDB/control02.ctl',
 '/u02/app/oracle/oradata/ORCLCDB/control03.ctl'
SCOPE=SPFILE;

- Restart the database to apply the change:

SHUTDOWN IMMEDIATE;
STARTUP;

Performance and Reliability Benefits:

• High Availability:
  • Prevents database downtime due to control file corruption or hardware failure.
• Fault Tolerance:
  • Oracle automatically updates all multiplexed control files simultaneously, providing redundancy without performance penalties.
• Easy Recovery:
  • Faster recovery from failures without the need to restore control files from backups, minimizing downtime.

Recommendations for Multiplexing in Oracle 19c:

• At least two or preferably three control files.
• Place copies on different physical disks or storage systems to further mitigate hardware failure risks.
• Regularly verify the status of control files through dynamic views like v$controlfile.

Checking Control File Multiplexing Status:
To confirm successful multiplexing:

SELECT name FROM v$controlfile;

This will show all active control files.
Conclusion Multiplexing control files is a best practice in Oracle 19c databases, greatly reducing the risk of downtime, data loss, and recovery complexity. This ensures that your database remains highly reliable, robust, and easier to manage.
In the next lesson, you will learn what it means to multiplex a control file and why that is important.