Re: Hot backups vs. Offline Backups

In article <4b6ph9$hp6_at_ixnews2.ix.netcom.com>, chuckh_at_ix.netcom.com (Chuck Hamilton) wrote:

> 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?

Naturally.  

>
> 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?

Of course.

> 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?

No.

Active transactions are recovered from the Redo Log archives, not the tablespaces.

That's why it's called a *Redo* log! :-)

graeme

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