Automatic Undo Managment on 9i

[DA Morgan]

Timmy Sin wrote:

> Hi All,
>
> I am upgrading from 7.X to 9i Rel. 2.
> Should I use the new feature of automatic undo management or keep on using
> rollback segments?
> Is the new feature reliable?
>
> Thanks in advanced.
>
> Regards,
> Timmy Sin

Go with UNDO.

I have experience no problems with 9.2. And not heard of anyone that has.

Daniel Morgan

[Timmy Sin]

Thanks Howard and Daniel.

So, I can just create a single undo tablespace, enable it to be AUTOEXTEND
and no more administration and sizing is required.

How about the feature "local management tablespace" already available in 8i?
Are you using them or the dictionary management tablespace?

Thanks,
Timmy

"Timmy Sin" <tswsin@yahoo.com> ¼¶¼g©ó¶l¥ó·s»D
:atpihg$nkn$1@news.hk.linkage.net...

> Hi All,
>
> I am upgrading from 7.X to 9i Rel. 2.
> Should I use the new feature of automatic undo management or keep on using
> rollback segments?
> Is the new feature reliable?
>
> Thanks in advanced.
>
> Regards,
> Timmy Sin
>
>

[Richard Foote]

"Niall Litchfield" <n-litchfield@audit-commission.gov.uk> wrote in message
news:3e01903f$0$248$ed9e5944@reading.news.pipex.ne t...

> "Timmy Sin" <tswsin@yahoo.com> wrote in message
> news:ats1in$h0u$1@news.hk.linkage.net...

> > Thanks Howard and Daniel.
> >
> > So, I can just create a single undo tablespace, enable it to be

AUTOEXTEND

> > and no more administration and sizing is required.

>
> Yes you can just create a single undo tablespace, I think I'd recommend

this

> though you might wish to stripe it across several disks for performance.

I'm

> not a big fan of autoextend (and certainly not without maxsize set)
> especially for UNDO as this would be a good way to fill a disk

unexpectedly.

> It is also not true that NO administration and sizing is required, just
> less. You don't have to worry about how many rollback segments and what

size

> they should be, you do need to worry about the undo retention period and

how

> much undo space you need.

Hi Niall,

Totally agree ...

> >
> > How about the feature "local management tablespace" already available in

> 8i?

> > Are you using them or the dictionary management tablespace?

>
> I can think of almost no downsides to use of LMT's, and a whole host of
> advantages especially if you do the sensible thing and go for a uniform
> extent size. As of 9.2 even the system tablespace is locally managed which
> should tell you something.

I can think of one downside. The fact you can't specify maxextents.

IMHO, a potential pain in the butt and one for which I've heard no sound
reason.

Picky ain't I :)

Richard

[Pete Sharman]

In article <3E00BB1A.2345C019@exesolutions.com>, DA says...

>
>Timmy Sin wrote:
>

>> Hi All,
>>
>> I am upgrading from 7.X to 9i Rel. 2.
>> Should I use the new feature of automatic undo management or keep on using
>> rollback segments?
>> Is the new feature reliable?
>>
>> Thanks in advanced.
>>
>> Regards,
>> Timmy Sin

>
>Go with UNDO.
>
>I have experience no problems with 9.2. And not heard of anyone that has.
>
>Daniel Morgan
>

There are some rare scenarios where AUM can be painful. IHAC who starts up the
database and then hits a transaction throughput of 16,000 TPS within 8 minutes
of starting the database. The system simply gets clogged trying to add
sufficient undo segments, since we don't keep a memory of how many there were
when the database was last shutdown. Of course, we start the database with 10
undo segments and then allocated more as needed. With this extremely unusual
client configuration, AUM was killing the performance until we had created
enough undo segments, so we swapped them back to rollback segments where we had
preallocated sufficient numbers.

Obviously, a very unusual case. Most clients I've dealt with work fine with
AUM.

HTH. Additions and corrections welcome.

Pete

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