Re: why need to backup undo tablespace?

niy38 wrote:

> Howard J. Rogers wrote:
> 

[snip]

>> 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.

It *is* a data file. It might be a slightly special one functionally, as far as the database is concerned, but it is just another datafile at heart. That you acknowledge it is as important to back it up as any other data file is critical, and should be the thing which anyone reviewing this thread in months or years to come latches on to.

That you can make a recovery work without an undo tablespace is one thing, and is just about justifiable in theory. The issue -the *practical* issue- is: can you *guarantee* that it will work for all Oracle versions, with and without RMAN, hot and cold, and without invalidating your support contract, on all O/Ses? And underlying that question is another: have you tested your undo-less recovery mechanism under all possible scenarios and circumstances?

Because unless you can do that, your later statement that backing up the undo tablespace is merely 'a convenience, not a must' is simple 100% wrong. 100% wrong, at least, for anyone running Oracle in a production,   business, real-world, environment.

And never mind that in 9i and above, your advice would rob me of Flashback capability... and that means I can't avoid performing an incomplete recovery in some scenarios, and those scenarios would thus result in data loss when they otherwise wouldn't have needed to.

It really is a non-starter to advocate as you do.

Regards
HJR Received on Sat Dec 11 2004 - 20:54:06 CST