Re: Hot backups vs. Offline Backups

chuckh_at_ix.netcom.com writes in article <4b6ph9$hp6_at_ixnews2.ix.netcom.com>:
>
> Peter Moore <pt_at_chaff.demon.co.uk> wrote:
> >Those people who think that you can't back up an open and active Oracle
> >database are *WRONG*.
 

> >If you are running Oracle7 you can backup a database while it is in use.
 

> >There are only two provisos:
 

> > 1) You are running in ARCHIVELOG mode.
> > 2) You issue the ALTER TABLESPACE name BEGIN/END BACKUP commands
> > before/after backing up the appropriate data files.
 

> >As long as you ensure that you also take backups of your control files and
> >archivelog files at the same time you will have no problems.
>
> What happens to your database integrity in the following scenario:
>
> 1. you're in the middle of a hot backup of tablespace 'a'
> 2. during that backup, a transaction occurs that effects objects in
> tablspaces 'a' *and* 'b'?
> 3. you finsish the hot back up of 'a' and being a hot backup of
> tablespace 'b'.
>
> If you have to restore both tablespaces, will you still have database
> integrity?
>
> I could be wrong and please correct me if I am, but wouldn't the
> backup of tablespace 'a' be missing parts of the transaction that the
> backup of tablespace 'b' contains? And if so, then don't you have to
> do an ALTER TABLESPACE x BEGIN/END BACKUP on all tablespaces that
> might be updated during the backup?
> --
> Chuck Hamilton
> chuckh_at_ix.netcom.com
>
This is why the database has to be in archivelog mode.

If you restore tablespace 'A', then the timestamps of the datafiles of tablespace 'A' is older than tablespace 'B'. Before you can open the database, you have to do media recovery where all missing updates are reapplied to tablespace 'A'; this information comes from the online and, possibly, from the offline redo-logs.  

> Never share a foxhole with anyone braver than yourself!
>
>
Willy Klotz

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