If we talk only about hot backups, and not about restore or recover.
in begin backup mode SCN in header of datafile is frozen and
1. data is updated in datafiles when ever a DML is fired
2. and SCN in updated after finishing backup i.e end backup mode taking the information from checkpoint.
1. why database is required to be in archive log mode for taking hot backup?
2. is the REDO or Archived REDOs are used by datafiles during the backup phase or after completing the backup.
3. if not, then what is the requirement to keep database in archive log mode.
with thanks to davey23uk, What is the necessity to keep database in Archive Log Mode to take hot backup, I mean what actually happens inside, such that archive log mode is required, if not hot backup cannot be taken.
with thanks to davey23uk, what i understood is changes are always written to redo log. if DB in archive mode, on log switch archive is generated, if in no archive mode, changes are lost the moment redo log group is used again.
During hot backup, changes are written in datafile and recorded in redo logs.
then why the archive log mode is required (not concerning to restore and recover). (i understood db should be in archive log mode, what i want to know is what's happening internally during hot backup, such that archive log mode is required)
great information, but one query, once we end hot backups,SCN in datafile header is updated to current scn, at that time do any changes, inserts happened during backup are written to datafile from archived redo logs. if not then why it is compulsary to put database in archive log mode during hot backups?.(i am not concerned about restore and recover but only about hot backup process)