Every Oracle database has a control file.
that must be opened for database operation to proceed.
A control file contains also entries that specify:
- Database name
- Timestamp of database creation
If the physical makeup of the database is altered (for example, if a new datafile or redo log file is created), then the control file is automatically modified by Oracle Database to reflect the change. A control file is also used in database recovery.
If the control file can't be read the database doesn't know what else exists! This is why you should be careful to keep good backups of your control files using plain of system backups. This is also why Oracle maintains multiple copies (typically 3) of the control file for safety. It multiplex the control file, that is, simultaneously maintain a number of identical control file copies, to protect against a failure involving the control file.
Control files in Data Dictionary
select name from v$controlfile;