Re: Redo log and rollback segment?

Hi Doug,

I'm not Tom, but it is correct that there are both before and after images. Becaus Redo is information to redo database changes, it contains the before image from a block change in a rollback segment and the after image from the changed data block.

--
Best Regards,

Ralph Ganszky

• The above opinions are mine and do not represent any official
• standpoints of my employer or third party organizations.

Doug Cowles wrote:

> I think you explained in a thread a few months ago that redo actually contains both
> before and after images. Is that correct?
>
> Thomas Kyte wrote:
>
> > A copy of this was sent to jonathan_at_ms35.url.com.tw (Trister Yang)
> > (if that email address didn't require changing)
> > On 3 Sep 1999 02:10:10 GMT, you wrote:
> >
> > >I always so confuse about what's different between redo log and
> > >rollback segment ?
> > >
> > >I will appreciate for your answer!
> > >
> > >Thanks!
> >
> > REDO is 'redo' -- it can redo a transaction. It is after images of changes. It
> > is predominantly used for RECOVERY after a crash or media failure.
> >
> > ROLLBACK is 'undo' -- it can undo a transaction. It is before images of
> > changes. It is predominantly used to rollback a transaction after an online
> > error or to provide read consistent, nonblocking views of data.
> >
> > --
> > See http://govt.us.oracle.com/~tkyte/ for my columns 'Digging-in to Oracle8i'...
> > Current article is "Part I of V, Autonomous Transactions" updated June 21'st
> >
> > Thomas Kyte tkyte_at_us.oracle.com
> > Oracle Service Industries Reston, VA USA
> >
> > Opinions are mine and do not necessarily reflect those of Oracle Corporation
Received on Sun Sep 19 1999 - 06:48:52 CDT