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Lesson 3Database control file introduction
ObjectiveDiscuss the use of database control files.

Database Control File

The control file contains information about all the files associated with your Oracle database. This is one of the files read during the startup of your instance to help determine the integrity of your database. If your database's control file is corrupt, the database cannot be mounted. If your database starts, you know your control file is good.
Recovering your database is very difficult without a good control file, so it is highly recommended that you maintain multiple copies of your control file and store each one on separate drives with separate controllers. You should also make sure the control file(s) are backed up on a regular basis. If your only control file becomes corrupted, recovery becomes more difficult. We will cover the process of multiplexing your control files later in this lesson.

Oracle 13c Control file Components

Question: How many sections does the control file contain in Oracle 13c?
In Oracle 13c, the control file is a crucial component for maintaining the integrity and consistency of the database. The control file is divided into six primary sections to manage different aspects of the database. These sections are:
  1. Header: The header section contains essential information such as the control file's structure, version, and compatibility. It ensures that the control file is compatible with the current Oracle 13c version and the database.
  2. Database Information: This section stores crucial database information, including the database's unique identifier (DBID), creation timestamp, and system change number (SCN). This information is necessary for recovery operations and ensuring database consistency.
  3. Checkpoint Information: Checkpoint information is vital for database recovery and instance recovery. This section maintains a record of the most recent checkpoint for each datafile and redo log file, enabling Oracle to recover the database to a consistent state in case of a failure.
  4. Redo Log Information: The redo log information section maintains details about the redo log files, such as their sequence numbers, sizes, and status. This information is critical for database recovery and maintaining a continuous record of changes made to the database.
  5. Datafile Information: This section contains information about all datafiles associated with the database, including their filenames, sizes, and status. Oracle uses this information to manage the datafiles and ensure data consistency during recovery operations.
  6. Archive Log Information: The archive log information section records details about the archived redo log files, which are essential for media recovery. This section helps Oracle identify the correct archived redo logs required for a successful recovery operation.

In summary, the control file in Oracle 13c is broken down into six primary sections, each responsible for managing different aspects of the database to ensure consistency, integrity, and efficient recovery operations.

Control File Sections Legacy

The control file is broken down into 17 sections (12 more than Oracle7.) This is a binary file and can not be viewed or directly modified using a standard editor. Among other things, a control file contains information such as:
  1. The names and locations of associated data files and online redo log files
  2. The log history
  3. Archived log information
  4. Backup set and backup piece information
  5. Backup data file and redo log information
  6. The current log sequence number
  7. Checkpoint information

You will not be tested during the OCP exam on the different sections of the control file. You should know that it contains information about the above sections and that this information is updated on a regular basis. I will indicate when the control file is being updated where appropriate.
The next lesson is about control file maintenance.