Re: Rollback performance and delete

"Alex Filonov" <afilonov_at_pro-ns.net> wrote in message news:8u7chm$3mn$1_at_nnrp1.deja.com...
> In article <3A06DE5D.30933844_at_motorola.com>,
> Allen <allen.brost_at_motorola.com> wrote:
> > I have looked through the Oracle documenation to understand exactly
 what the
> > rollback segment is doing during a DELETE and I am still a little
 confused with
> > the results I am finding.
> >
> > I am doing a delete of a large table. The table is 5G. I am deleting
 about 1G
> > of the the table.
> >
> > I have created a large rollback segment to handle the transaction and
 I have set
> > the size of the rollback segment to about 2G. I figured that this
 should be
> > plenty. When I do the delete, I see the rollback segment grow to 5G.
 I don't
> > understand this. I thought the rollback segment held all of the
 original rows
> > before the change. If this is so, then I would expect to see about 1G
 in the
> > segment. It seems like Oracle is copying everything in the table to
 the
> > rollback segment. Anyone know why?
> >
> > - Allen
>
> Oracle copies before image copies of all changed blocks into the
> rollback segment. So if your 1G of deleted data spread over 5G of
> data blocks, 5G will be written into rollback segment.

If you are suggesting that an update to one record will result in the entire block being copied into rollback, then that's not correct.

Regards
HJR
> >
> >
>
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
Received on Tue Nov 07 2000 - 00:44:06 CST