Howard, does UNDO tablespace need to backup?
"Howard J. Rogers" <hjr_at_dizwell.com> wrote in message
news:3fa9829d$0$9607$afc38c87_at_news.optusnet.com.au...
>
> "John" <jbradshaw777_at_yahoo.com> wrote in message
> news:f2f59d82.0311051457.66d575ac_at_posting.google.com...
> > "Howard J. Rogers" <hjr_at_dizwell.com> wrote in message
> news:<3fa94dae$0$3787$afc38c87_at_news.optusnet.com.au>...
> >
> > > > 2. Can a transaction span more than one rollback segment?
> > >
> > > No. If it starts in one rollback segment, it must finish in that
> rollback
> > > segment. In 9i, with "undo segments" (which are just rollback segments
> with
> > > a different name) that's modified slightly because one segment can
> 'steal
> > > extents' from another, and so a transaction can indeed appear to cross
> > > between segments. But that's uniquely 9i.
> > >
> >
> > Thanks, Howard. Speaking of 9i AUM, are you aware of anything problmes
> > associated with it?
>
> Yes, one or two. Check out Metalink, because they are all platform-specific.
> There used to be dozens (we're talking bugs here). I wouldn't have touched
> it in 9.0.1, but most seem fixed in 9.2. But check.
>
> In terms of whether a (hypothetically) bug-free implementation has intrinsic
> problems, yes there are still some gotchas. The one I fell into was creating
> enormous undo tablespaces because flashback seemed such a good idea, and I
> had the disk space. Unfortunately, having oodles of free space left causes
> Oracle to put off the day when new transactions start sharing existing undo
> segments: Oracle tends to create new undo segments for each new transaction
> until space pressure is felt (it's a complex algorithm, so it's not that
> 'pat', but it's along those lines). Net result: huge tablespace means lots
> of undo segments. Each undo segment has a segment header block. Therefore,
> huge tablespace means lots of undo segment header blocks clogging up my
> buffer cache.
>
> But, sized appropriately, I actually quite like AUM. But ask Jonathan: he's
> not so keen on it, I think.
>
> >It's been around for more than a couple of years,
>
> Not really. I seem to recall teaching one of the first 9i courses in Oz
> around about August last year. So just over a year and a bit. It's still not
> totally mature, I think.
>
> > I would assume most of the kinks would have been fixed by now.
>
> Assuming anything is always risky! Particularly with AUM. It's pretty close,
> and I've never encountered any disasters with it, but check Metalink very,
> very carefully.
>
> >What do
> > you think of the old dictionary views like v$rollsats and
> > dba_rollback_segs? Some of the stuff in there do not make much sense
> > anymore. 'Optimal' for example.
>
> Worth the price of the upgrade on its own, v$undostat is your friend,
> whether you choose to run AUM or not. Tells you your max concurrency, the
> longest running query, and out-of-space error counts. Brilliant stuff. The
> old stuff is still there, true. But I haven't looked at them for a while
> (v$rollstat is still useful for finding out which specific undo segment has
> been used to house a transaction's undo, though).
>
> Regards
> HJR
>
>
>
> >
> >
> > John
>
>
Received on Wed Nov 05 2003 - 17:50:20 CST
