Re: Space wasted because of automatic undo management

Vsevolod Afanassiev wrote:

> Let's say I am using traditional rollback segments. For a small
> database I would create 4 segments, each 100 MB in size, and set
> OPTIMAL to 100 MB. All 4 segments will be in the same tablespace and in
> the same datafile, so initial datafile size will be 400 MB.
> It may grow if there is a large transaction, but eventually the
> transaction will complete, rollback segment shrink back to OPTIMAL
> size, and the datafile could be resized back to 400 MB. So the space is
> used efficiently and not wasted.
>
> It appears that with automatic undo management the space is being used
> very inefficiently. Oracle creates additional extents all over the
> place, with total disgregard for disk space. There are huge chunks of
> empty space between individual extents. I am thinking about switching
> back to traditional rollback segments.
>
> Any thoughts?
>
> Thanks
>
> Sev

Your assumptions regarding your "best practice" around rollback segments is in error and thus leading you to an incorrect conclusion.

Setting OPTIMAL was a bad practice and if you are so close to running out of disk that recovering a few hundred MB makes a big difference then you have bigger problems.

Given the price of disk ... handcuffing one's self with RBS when AUM is so incredibly superior makes no sense. I'd suggest forgetting about disk space and concentrating on something else.

-- 
Daniel A. Morgan
University of Washington
damorgan_at_x.washington.edu
(replace 'x' with 'u' to respond)