Archive Log Mode during Hot Backups

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.

if so
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 regards

depends how you are doing the backups

It's all depends on your business requirement whether the database is on archive log mode or noarchive log.

In case any mishaps like database crash or accedentally deleted table(s) or datafile(s) or tablespace(s) ...

If your business can effort to loose the data from last full backup to the time of mishap then you can put the database in NOarchivelog mode.

If your business needs to recover every thing upto the time of mishap then you should put the database in archivelog mode.

Thanks,

with thanks to tummala, can we take successfull hot backup(db up and runing) in no archive mode.(not concern to restore or recovery)

if not, then what is the role of REDO log and Archived logs in hot backup process.

with regards.

no you cannot

and they have the same role as they do when there isnt a backup - recording changes

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 regards.

so what happens to the changes when the backup is taking place, if you don't have archive log mode where are those changes to be kept?

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)

with regards

Probably the below link clears your confusion.

http://advait.wordpress.com/2008/05/...kup-oracle-9i/

Thanks,

with thanks to tummala

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)

with regards

Quote:

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hot backups?.(i am not concerned about restore and recover but only about hot backup process)

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you SHOULD concern about restore and recover when are you trying to take the hot backup. Because, hot backup is not consistent and in case of recovery you should need archive logs to get back your data.

Thanks,

Quote:

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Originally Posted by prthvira

...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)

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The answer is pretty simple -providing you are not using RMAN you must put your tablespaces in backup mode, otherwise the backup you may take will be unrecoverable.

As you may remember in order to recover from a Hot Backup you have to do two different things...
1- Restore your Hot Backup
2- Recover the database -here is where archivelogs enter in the picture.
How does Oracle knows what has to be recovered from archivelogs?... looking at the SCN. If you never put your tablespace in backup mode SCN would not be frozen then Oracle wouldn't know what has to be recovered.

Hope this clarifies.