Re: Rollback performance and delete

From: Alex Filonov <afilonov_at_pro-ns.net>
Date: Mon, 06 Nov 2000 22:49:27 GMT
Message-ID: <8u7chm$3mn$1@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.
>
>

Sent via Deja.com http://www.deja.com/
Before you buy. Received on Mon Nov 06 2000 - 16:49:27 CST