Hot Backup Questions

[adewri]

Also my understanding is that when we give the alter tablespace end backup command all the redo generated during the backup is applied to the datafile to advance the datafile SCN to database SCN.

The same has to be done to the backup file to bring it to consistent state, hence the header is freezed so that oracle knows that redo generated between the SCN at begin backup and end backup need to be applied. (More ever the blocks changed during the backup are rewritten from the redo)

Or in other words if the SCN were not freezed, they would also be copied in the backup datafile. So how would oracle know if the datafile is inconsistent when its restored, as the SCN of the backup datafile would match the SCN at the alter tablespace end backup command. And Oracle uses SCN numbers to apply the redo.

HTH