Re: 8i to 9i migration, performance issues

"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