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Re: 8i to 9i migration, performance issues

From: Paul <pkelley_at_coat.com>
Date: 30 Mar 2004 07:44:40 -0800
Message-ID: <473377b4.0403300744.4d535155@posting.google.com>


"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message news:<c32kh5$dm$1_at_sparta.btinternet.com>...
> Notes in-line.
>
>
> One of the disabled features is subquery unnesting,
> and one of the bugs in the 9.2 optimizer is the fact
> that the costing for unnested subqueries is extremely
> high (fixed in 10.1), so unnesting happens pretty
> much everywhere it can. This means you can end up
> with hideously inefficient unnests, where a filtered
> subquery would be much better.

From metalink:

"Please note that the decision to unnest a subquery is not costed in Oracle9i. The decision to unnest a subquery is taken based on a set of heuristics (rules) before the query is optimized." Received on Tue Mar 30 2004 - 09:44:40 CST

Original text of this message

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