Re: FYI: In 10.2.0.4 cardinality estimation change

From: 조동욱 <ukja.dion_at_gmail.com>
Date: Fri, 25 Apr 2008 09:47:58 +0900
Message-ID: <43c2e3d60804241747v241d0fd4pf25ff24411d3b6f6@mail.gmail.com>


The funny little thing is that this patch has introduced another bug 6082745.
What an irony. :)
(But these things always happen in Oracle)

2008/4/25, Riku Rsnen <riku.rasanen_at_kantamestarit.fi>:
>
> Found interesting change, included in 10.2.0.4.
>
> From Note:5483301.8
>
> Quote:
>
> "If a column has a frequency histogram and a query uses an equality
> predicate over the column looking for a value that does not exists
> in the histogram then the CBO was estimating a cardinality of 1.
> This could favor Nested Loops too much.
>
> The fix introduces a notable change in behavior: instead of estimating
> a cardinality of 1 then with this fix CBO estimates a cardinality of
> (0.5 * the lowest cardinality found in the histogram). This can result
> in plan changes."
>
>
>
> This issue has bitten me several times, mostly because of unnecessary
> histograms. Remains to be seen, if this really affects anything.
>
>
> --
> Riku Rsnen
> Kantamestarit Oy
> www.kantamestarit.fi
>
>
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

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Received on Thu Apr 24 2008 - 19:47:58 CDT

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