Re: Proving or Debunking the need for rebuilding

DA Morgan wrote :

> hasta_l3_at_hotmail.com wrote:
> > DA Morgan wrote :
> >> hasta_l3_at_hotmail.com wrote:
> >>>>> Is it possible what the OP is seeing is a delayed block cleanout?
> >>>> I think it is entirely possible. I'm wondering if simply doing a
> >>>> count(*) that uses the index in question, before performing each test,
> >>>> might shed light one way or the other. The idea is to visit all blocks
> >>>> and clean them.
> >>>>
> >>> We are deleting in a bunch of small transactions.
> >>> We should have (almost) no delayed block cleanouts, right ?
> >>>
> >>> --- Raoul
> >> Depends!
> >
> > Would you elaborate, Doug ?
> > I am not much familiar with this area.
> >
> > At commit time, blocks will be cleaned up if they are
> > still in the cache, right ?
> >
> > Off hand, I cannot think why (many) dirty blocks would
> > be written on disk :
> >
> > a) We have pretty big redo logs.
> > b) Checkpointing happens with low frequency
> > c) With high probability, we dont do huge selects
> > or table scans that would flush blocks out of the
> > cache.
> > d) The structure of an index does not massively
> > change when - say - ten or twenty rows are deleted,
> > right ? Or does it ?
> >
> > Anything I missed ?
> >
> > --- Raoul

>

Thanks for the pointer, Daniel..

However, after having read this thread, and after having re-read the section on block cleanout in Expert Oracle, I'm still confused on what you had in mind with "Depends" :-(

AFAICS, commit cleanout should take care of all modified blocks... Received on Tue Nov 28 2006 - 12:14:23 CST