On May 9, 11:51 am, Robert Klemme <shortcut..._at_googlemail.com> wrote:
> On 09.05.2007 16:58, Valentin Minzatu wrote:
>
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> > On May 9, 10:37 am, Robert Klemme <shortcut..._at_googlemail.com> wrote:
> >> On 09.05.2007 16:22, Valentin Minzatu wrote:
>
> >>> On May 9, 6:48 am, Robert Klemme <shortcut..._at_googlemail.com> wrote:
> >>>> Hi,
> >>>> this is on 10.2.0.1.0. I think I remember that there is a parameter
> >>>> that will affect how Oracle costs IO but can't seem to find it (searched
> >>>> DB Reference, Performance Tuning Guide, PL/SQL Package Reference, Web).
> >>>> Does my memory fail me?
> >>>> Do you know other ways to influence how Oracle costs single block reads
> >>>> vs. multi block reads (apart from DB_FILE_MULTIBLOCK_READ_COUNT and
> >>>> hinting that is)? Thank you!
> >>>> Kind regards
> >>>> robert
> >>> What is the problem you try to address by chaging the optimizer
> >>> behavior?
> >> I'm trying to bias the CBO towards multi block reads.
>
> >> Kind regards
>
> >> robert- Hide quoted text -
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> >> - Show quoted text -
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> > Why do you need to do that? (i.e. is this a DW system? )
>
> Si. And experiments have shown that plans with MBR's perform
> significantly better than those without. And I'd prefer to use DB
> parameters or other means over hints.
>
> Regards
>
> robert- Hide quoted text -
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> - Show quoted text -
You should have a very strong case when you make changes at the
instance level as they impact everything else in ways that are not
always predictable. The reason I asked you what are you trying to
achieve was to see if there are no other ways to accomplish the same
goal without impacting the whole (i.e. build another level on the top
of the building without having to make changes to the foundation). If
you are only to look at how much testing would involve validating the
one change at the database level - that is a lot. Unless you have a
single application against that database I would try to look into
addressing the issue somehow else.
Received on Wed May 09 2007 - 10:59:51 CDT
