Re: re-indexing per statement or per row?

"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message news:1018297158.13402.0.nnrp-14.9e984b29_at_news.demon.co.uk...
> >This opens up a whole interesting can of worms for me because I *know*
(cos
> >the docs and folk like Howard have told me so) that *in backup mode* that
> >redo is generated for the whole block rather than the modified record(s)
> >(assuming archivelog mode). Yet this is leading to a suggestion that redo
> >*can* be in someways a snapshot of block level changes. which raises the
> >question of how ordinary redo differs from *backup* redo.
> >
>
>
> I doubt if Howard told you that, as it's not quite true. In backup mode,
> there is a very specific condition under which the entire current block
> is copied into the redo buffer before the normal redo record is generated.
> And contrary to common belief, this extreme action is not taken for
> every redo change generated for the block.

My turn to clarify my statement - I had intended the I *know* above to be taken as an admission that what I knew was in fact provisional and probably wrong - it often is. What I understood from Howard is not necessarily what he has written :-( . What you say is relevant as I was a holder of the common belief that in backup mode whole blocks were always copied into redo it is interesting to learn that this is wrong.

Having said all that the column in v$transaction that you point us at is used_urec or used undo records and undo is not redo as I know well, but managed to confuse above in any case. So unless used_urec actually referred to redo my whole argument above is completely baseless. Had to get that off my chest as I woke at 2 am this morning realising my foolishness.

--
Niall Litchfield
Oracle DBA
Audit Commission UK
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