Re: Question about Undo segments

As a followup on this auto vs manual redo/undo...

If you are running 9i in auto redo mode, can a session specify that it wants to use an old fashioned manual RBS (via SET TRANSACTION) for a redo intensive load job?

tx
Peter

"Howard J. Rogers" wrote:
>
> "Md Irfan" <irfan_pk_at_hotmail.com> wrote in message
> news:c42168e7.0204280827.47e90793_at_posting.google.com...
> > "Howard J. Rogers" <dba_at_hjrdba.com> wrote in message
> news:<aafd03$9ki$1_at_lust.ihug.co.nz>...
> > > Undo segments are just rollback segments with a new name. Therefore,
> what
> > > was true for rollback segments remains true for undo segments.
> >
> > But I have seen there are both RBS and Undo Tablespaces in 9i. Which one
> is
> > used for rollback.
> > Is data written in both the tablespaces?
> >
>
> No. "Undo segment" is just the name we give to rollback segments when 9i
> uses the automatic method of managing them. If you use the manual method of
> managing them, they are still called rollback segments. Obviously you can't
> simultaneously be using both the automatic and the manual method of managing
> them, so it is impossible to have both undo segments and rollback segments
> being used simultaneously. It's one or the other.
>
> Set undo_management=MANUAL, you have rollback segments. Set
> undo_management=auto, you have undo segments. Which ever one you are NOT set
> to, if it exists at all, remains dormant and unused. If you've created
> rollback segments, and switch to AUTO, those rollback segments are not
> written to at all. If you have an undo tablespace and you switch to MANUAL,
> the undo tablespace is not used at all -it's just dead disk space.
>
> Regards
> HJR
>
> > >
> > > Therefore, it's your server process that modifies undo buffers. They get
> > > flushed to disk as dirty buffers whenever DBWn takes it into its head to
> do
> > > any osrt of disk writing. The redo for them is the same as it is for any
> > > modification to any buffer: the before and after image.
> > >
> > > In short, there's nothing magic about them -and if you know how rollback
> > > blocks are dealt with, that's how undo blocks are managed, too.
> > >
> > > Regards
> > > HJR
> > >
> > >
> > > "Jargular" <zclai_at_yahoo.com> wrote in message
> > > news:8ae4ae9e.0204270719.22c0f769_at_posting.google.com...
> > > > Hi,
> > > >
> > > > Does anybody know what is the process that writes to the Undo
> > > > segments? under what condition the Undo buffers are flushed into Undo
> > > > segments? how are the changes in Undo buffers recorded in the online
> > > > Redologs? I seached Oracle9i documentation, it seems that they are not
> > > > detailed in the docs. Anyone can help?
> > > >
> > > > really appreciated.
> > > >
> > > > Jargular
> > > > zclai_at_yahoo.com
Received on Mon Apr 29 2002 - 12:51:25 CDT