Re: reference cursors

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Fri, 30 Jan 2004 22:01:26 -0000
Message-ID: <000601c3e77c$9b8c25c0$6702a8c0@Primary>

Sorry,

Ignore the last post - I've just checked the 10 Beta manuals. The way you've used the hint, it is supposed to specify the single table cardinality for each of the four tables after application of any single-table (i.e. non-join) predicates on those tables.

Regards

Jonathan Lewis
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Original Message ----- From: "Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> To: <oracle-l_at_freelists.org> Sent: Friday, January 30, 2004 4:44 PM Subject: Re: reference cursors

>
> According to the 9.2 manual, the cardinality() hint
> should take a list of table aliases, and a cardinality.
> Then when that list of tables starts the join order,
> the cardinality of the join up to that point is what
> you have specified.
>
> Consequently the four separate cardinality hints
> in your query are saying:
> if you start with t1, the cardinality from t1 is 10
> if you start with t2, the cardinality from t2 is 10
> if you start with t3, the cardinality from t3 is 10
> if you start with t4, the cardinality from t4 is 10
> This may not be what you intend. As a consequence, it
> is possible that some other small effect relating to ref
> cursors or dynamic sql is causing a different table ordering,
> and a dramatic change in the statistics that Oracle is
> required to use.
>
> L:ine 11 may be a big part of your problem. Oracle assumes
> the cardinality of a table cast() is 8,168 - but your run time
> stats show 2 rows returned.
>
> Regards
>
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>

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Received on Fri Jan 30 2004 - 16:01:26 CST