Configuring the snapshot control file

It is common knowledge that data files can be backed up when the database is open. This option is called the hot backup or open database backup. It is possible because even when the files are being constantly modified and are inconsistent, they can be made consistent by using archived log files in the recovery stage. Creating a consistent file is imperative as otherwise the database can't be opened. Archived logs are self-contained anyway, so taking their backup with an open database is not an issue. However, in the case of the control file that always gets updated, a hot backup of it won't be usable at all. This presents an interesting issue, but fortunately, a solution to tackle it is available with RMAN in the form of a snapshot control file!

A snapshot control file is the point-in-time copy of the current control file when its backup is initiated in the open database mode. This is not really the backup of the control file (though it can be used as...