Recover database using Backup Controlfile until cancel

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What's checked or what happens when we "run recover database using Backup controlfile until cancel;"? What is the does this command?

If you were to recover the database with a current control file, Oralce'll know the last SCN of the last checkpoint. So, Oracle can use the information on the archived and online redo logs to apply recovery up to that SCN. This was called a "complete" recovery.

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If do not has the current control file, your option was to use a backup controlfile. Which means Oracle does not know the SCN to stop applying recovery. So we tell Oracle that is using a "backup Controlfile" and that you'll tell it when to stop applying redo by reply ing "Cancel." When Oracle starts recovery, it looks at the datafiles to know the last time a checkpoint is performed on the datafile. Oracle now knows to start applying recovery to the datafile for all Scns after the SCN in the datafile header. Oracle rolls forward transactions. But the Oracle does not know if to stop, and eventually, the Oracle applies recovery in all of your archived redo logs. You can then tell Oracle to use the redo in the online redo logs. Oracle would ask you where to find more redo. At the this point, the it to quit applying redo by replying CANCEL.

Hopefully, you never has to use the This command. This is because multiplex your control files and has three copies of the control file, all on different disk units. If you lose a disk unit, you use the control files on the other disk units. The only time you need this command was when you lose all of the your control files. Either use a binary backup of the control file or re-create the control file with the Create Controlfile Command and then recover with the backup control file.