For the close backup, it's obvious we don't have to
backup undo: you even can create a new one after deleting
the original one.
This is quite understandable: since after shutdown
(normal, transactional, immediate), all transactions
are over. ( here I didn't consider undo_retention)
So I suppose for a must of backup undo, it's hot backup.
For an tablespace USERS, after I do a hot backup,
and its datafiles corrupt, now I do recovery, do I
need undo?
Howard J. Rogers wrote:
> niy38_at_hotmail.com wrote:
>
>> as subject.
>>
>
> I am at a loss to know what would prompt such a question!
>
> Why back up *any* tablespace? Because it contains data that needs to be
> preserved and recovered. The one tablespace that's not true for is the
> TEMPORARY tablespace.
>
> Undo segments are segments, just like tables and indexes are segments.
> It just happens that the data they contain is for Oracle's housekeeping
> benefit, and not for your edification and delight. But it's data
> nonetheless, without which Oracle cannot maintain read-consistency or
> transaction rollback functionality, and lots else besides.
>
> You presumably care about your tables and indexes, so you back them up.
> Oracle similarly cares quite a lot abouts *its* 'tables' -ie, the undo
> segments. They need backing up accordingly, too.
>
> I don't understand why you would even begin to think that they were
> somehow disposable or dispensible... but that's simply because I can't
> see inside your mind to see the thought processes that lead to the
> question. If you care to be a little more expansive about why you
> thought/think they might be capable of being not backed up, perhaps I
> can help clarify the matter better for you.
>
> Regards
> HJR
Received on Thu Dec 09 2004 - 10:43:04 CST
