Oracle Control File multiplexing

There are a lot of operations on the Internet about control files, I probably looked down. A lot of them are scrambled to go around. The following is an example of how Oracle's control files are described in its own understanding and operations.

First introduce the control file

In the Oralce database, the control file is a small binary file, and the general size is automatically created around 10MB when the database is created and updated when the database changes. Control files are constantly updated and the control files are guaranteed to be available at all times. Control files play an important role in Oracle, and the database that has no control files or control files must be down. The control file contains database structure information, data files, and log file information.

Because the control file is important in the database, it is important to protect the file. Therefore, it is recommended to use the multi-path control file or backup control file method. When the control file is corrupted, the user can restore the control file through a backup. The system provides manual creation and backup of control files into textual form to provide more flexibility in managing and protecting control files. The control file records the corresponding database structure I information such as: Data file, log file name and location and the current parameter location, which mainly includes the following:

1. Database name and SID identification.

2. List of data files and log files.

3. Time stamp for database creation.

4. Tablespace information.

5. The current redo log file sequence number.

6. Archive log information.

7. Check point information.

8. Start and end of the rollback segment.

9. Back up data file information.

Data files are so important how do we manage the control files on a daily basis?

(1) Timely backup of control files

The control files of an Oracle database are created automatically when the database is created, and in general, the control file should have at least one copy (at least two control files, placed on different disks, to ensure that data rollback occurs when the data is abnormal). When an instance of an Oracle database is started, The control file is used to establish an association between the database (including: Data files, control files, and log files) and instances. Must be opened during data manipulation. When the physical composition of the database (adding a log file) changes, Oracle automatically logs this change to the control file. If the physical composition of the database has changed, the user is established to back up the control files in a timely manner.

(2) Protection of control documents

When the control file is corrupted, the database will not start. And the repair is difficult. The control file plays a role in the database operation. Because the control file plays a very important role in the entire database, Therefore, it is necessary to use various policies or guidelines to protect the control files when managing the control files. The current method is multiplexed control files and backup control files. How to multiplex the control file, in the initialization parameter Control_ File lists all the control file names for the current database. Oracle will modify all control files at the same time based on the information in the Control_file parameter, but only the information in the first control file. In addition, it is important to note that during the entire data run, If any of the control files are corrupted, the instance cannot continue to run. Multiplexing of control files consists of two steps to change the Control_files parameter and copy the file, as follows:

1. Change the control_files parameter.

A. Set the multipath parameters and the control file should be saved under a different disk file.

2. Implement the backup operation of the file.

A. Implement A backup mechanism for the control files.

Oracle Control File multiplexing