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The oracle database control file is a very important file. It is a binary file automatically generated when the database is created, which records the status information of the database and mainly includes the following contents.

The name of the 0 database. A control file can only belong to one database.

The time when the database was created

The name, location, online and offline status information of the @ data file

The name, location and archiving information of the redo log file

All tablespace information

The current log serial number

Recent checkpoint information

The control file is read in the Mount phase of database startup. When the database is started, the default rule is used to find and open the parameter file, and the location information of the control file is contained in the parameter file. After opening the control file, the database will be opened through the location of various database files recorded in the control file, thus starting the database to the available state. When the database is started successfully, during the operation of the database, the database server can constantly modify the contents of the control file, so when the database is opened, the control file must be readable and writable. However, no other user can modify the control file, and only the instance of the database can modify the information in the control file.

To view the control file information, you can view the control file information and control the file name from the V$controlfile view

In addition to viewing control file information from the V$controlfile view, you can also view it from the V$parameter view

How to view the content information stored in a control file

You can use V$controlfile_record_section

View type,record_size,records_total,records_used in V$controlfile_record_section

From the screenshot, you can see that the control file stores information about the creation of the database, redo log information, data files and archived log records and other information. This valuable information is used for data maintenance and management, and many data dictionary views are information obtained from control files.

Store multiple control files

Because the control file is very important, it requires that there can be not only one control file, usually more than 3 control files in the database, and stored on different disks. This method of using control files is also known as the multiplexing of control files. One way to achieve multiple is to copy the control file to multiple locations and modify the CONTROL_FILES parameter in the initialization parameter file to include all the control file names. It is important to note that when there are multiple control files, oracle updates all control files at the same time, but only reads the first control file listed in CONTROL_FILES.

An example is given to illustrate the method of multiplexing control files.

The database state is open. Modify the CONTROL_FILES parameter in SPFILE

Shut down the database

Use operating system commands to copy files to a new location

Restart the instance

Backup control file

Backup control file

In order to ensure the security of the database, the control file is backed up when the location information of the data file or log file changes, such as when the data file is added to the tablespace. There are two backup methods: backup as binary file and backup as script file

Give an example of how to back up as a binary file:

Check how many control files exist in the current system before backing up control files

Backup control file

Modify system parameter file

An ORA-00214 error was reported after starting the database after shutting down the database, due to inconsistent versions of the control files

The version of control01.ctl control file is 817, and the version of control02.ctl is 806.

Use control01.ctl to overwrite control03.ctl to keep the version of the control file consistent.

Shut down the database

Just restart the database.

Restore control file

Assuming that the control file specified by CONTROLD_FILES is corrupted, but the control file can still be accessed in the data dictionary, you can use the following steps to recover:

Close the database instance

Delete control file

Start the database

The status of the database at this time is

Overwrite the damaged control file with the intact control file with the operating system

Close the current database

Restart the database instance

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