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Re: Optimizer issue

From: Riyaj Shamsudeen <rshamsud_at_jcpenney.com>
Date: Fri, 19 May 2006 12:29:51 -0500
Message-ID: <446E008F.7060301@jcpenney.com>

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Hi

   Ask the vendor, for the code that breaks in CBO environment. Ask them what design do they have that will break in CBO environment. What plans do they have for migrating to higher versions, such as 10g in which rule based optimizer is desupported (not suggesting that RBO will not work in 10g) .

  If you are in 10g, then RBO is already de-supported and refer them to docid:*189702.1.*

Few lines from the above document:

" The RBO is Oracle's legacy optimizer originating from Oracle Version 6 and earlier. The RBO is being desupported in Oracle10g. The RBO will still exist in Oracle10g, but will be an unsupported feature and will be removed in a future release. No code changes will be made to the RBO code and no bug fixes will be provided. The RBO was superseded in Oracle7 by the CBO and has continued to be available for backwards compatibility. Oracle Oracle10g will support only one optimizer, and all applications running on that release should use that optimizer."    

Thanks
Riyaj

Manjula Krishnan wrote:
> I quote the vendor "the potential for displaced data (missing data on
> forms and reports) where statistics have been gathered. Missing data
> has been observed within the application under a strict RULE based
> environment where objects have been analyzed to gather statistics."
> What Riyaj said makes sense that without the order by clause, it will
> "appear" like data is missing.
>
> Riyaj: What did you mean by "code/strategy that will break" ?
>
> Thanks yall.
>
> Manjula
>
>
>
> On 5/19/06, *Riyaj Shamsudeen* <rshamsud_at_jcpenney.com
> <mailto:rshamsud_at_jcpenney.com>> wrote:
>
> Quoting Manjula:
>
> >>and some data would not be pulled up in the application. Is that
> possible?
>
> Huh ? Generally not possible. But, I know of one exception. I think
> Kirti Deshpande encountered this: One of the application was relying
> upon an index order to return the rows in a specific order. Optimizer
> selected a different index, after collecting statistics, affecting the
> functionality. Specifically, if the code is also interested in top N
> rows with this strategy, then incorrect (from the application point of
> view) will be pulled in to the application, causing user irritation.
>
> But, the problem here is that incorrect and potentially treacherous
> strategy. Unless 'order by' clause is used, RDBMS will return rows
> anyway it sees fit. So, you might want to ask them to provide more
> details as to exactly why collecting statistics will not work and ask
> for code/strategy that will break.
>
> --
>
> Thanks
>
> Riyaj "Re-yas" Shamsudeen
> Certified Oracle DBA (ver 7.0 - 9i)
> Allocation & Assortment planning systems
> JCPenney
>
> Manjula Krishnan wrote:
> > I have an application on Oracle 9i. The database (designed by the
> > vendor) was set with optimizer_mode=CHOOSE. A week after we went
> live
> > with the application, performance started degrading. I
> discovered that
> > statistics were missing and built them. Immediately the application
> > problems were resolved.
> >
> > The vendor claims that with the statistics, it would not use the
> right
> > indexes and some data would not be pulled up in the application. Is
> > that possible?
> >
> > Thanks,
> >
> > Manjula
>
>
>
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Received on Fri May 19 2006 - 12:29:51 CDT

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