Re: why need to backup undo tablespace?

From: niy38 <niy38_at_hotmail.com>
Date: Sat, 11 Dec 2004 15:37:53 -0700
Message-ID: <cpft0l$qom$1@onion.ccit.arizona.edu>

Howard J. Rogers wrote:
> Denis Do wrote:
>

>> On 2004-12-09, niy38_at_hotmail.com <niy38_at_hotmail.com> wrote:
>>
>>> as subject.
>>>
>>
>>  
>> As you know, in Oracle recovery process there are 2 stages:
>> - rolling database forward
>> - rolling uncommited transactions back
>>
>> Second step is impossible without RBS, and they are in UNDO
>> tablespace. 

>
>
> Actually, the first step is impossible, too. As a transaction is
> re-performed, we must re-generate the undo that was generated when the
> transaction was first performed. You need an undo segment for that, too,
> therefore.
>
> The whole thing is a major distraction in any case. The documented,
> supported, well-established rules are: you back up your control files
> and ALL data files, except for ones associated with temporary
> tablespaces, and you are permitted not to backup read-only tablespaces
> very often (though commonsense dictates you do it more than just once,
> which is the theoretical minimum).
>
> I have never even heard of anyone ever suggesting UNDO is somehow an
> exception to the rule before. I guess you just live and learn and should
> never be surprised at the levels of danger that some people are prepared
> to live with.
>

It's no doubt undo tablespace is a must for roll forward or rollback, and also I don't deny it's as important as backuping up datafiles. but the difference is: if you lose datafile and no backup, then you lose; but if you lose undo tablespace and no backup, you still can recreate the undo tablespace.

So backuping undo tablespace can bring convenience ( you don't have to recreate the undo tablespace), but it's just not a must. Received on Sat Dec 11 2004 - 16:37:53 CST