Re: question about automatic undo management

"Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message news:<PTlX9.29896$jM5.77257_at_newsfeeds.bigpond.com>...
> "Joel Garry" <joel-garry_at_home.com> wrote in message
> news:91884734.0301211649.2d029eda_at_posting.google.com...
> > "Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message
> news:<IegX9.29683$jM5.76837_at_newsfeeds.bigpond.com>...
> > > "Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message
> > > news:b0jcjl$igp$1$830fa78d_at_news.demon.co.uk...
> > > > Diskspace may be cheap, but I/Os are not, and
> > > > any strategy that results in redundant I/O is inherently
> > > > suspect. Allowing undo segments to become
> > > > unnecessarily large is one way of generating
> > > > redundant I/O.
> > > >
> > >
> > > But since SMON shrinks anything that it considers too large every 12
> hours
> > > or so, this isn't going to be an issue, is it?
> >
> > Sounds like the real world is bound to undo all gains from moving to
> > LMT's by simply requiring too much undo for useless flashbacks.
> >
>
> Too much undo is simply a question of storage. At this stage, unless
> Jonathan cares to clarify. Quite what benefits of LMTs that mitigates, I
> can't see. LMTs eliminate possible contention on UET$/FET$ data dictionary
> tables when allocating or deallocating space; they eliminate the possibility
> of tablespace fragmentation; they make segment sizing decisions a
> no-brainer. Now what has an 'excess' of undo to do with any of that?

Consider a humongous DW combined with a humongous transactional labor and inventory system with humongous RBS's and product planners running humongous part and labor allocation what-if scenarios for building jumbo-jets on it. For each what-if, when they are done, they flashback. At some point, they are doing so much undo I/O, it becomes substantially like the old contention problems.

jg

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