Re: Execution plan optimizer Question

There are a few conditions which make Oracle use cost based optimisation on a statement even when your system is set to RULE based, or even when you have a RULE hint.

To date the list is (I think) limited to statements containing at least one of the following:

An IOT
A partitioned table
The SAMPLE clause
A parallel enabled table or index.
ANSI outer joins (v9)

If any of your queries contain these types of objects, then in the absence of any statistics Oracle will use some default values - so when you get proper values in place the paths may change (in theory for the better).

Jonathan Lewis
http://www.jlcomp.demon.co.uk

Author of:
Practical Oracle 8i: Building Efficient Databases

Next Seminar - Australia - July/August
http://www.jlcomp.demon.co.uk/seminar.html

Host to The Co-Operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html

-----Original Message-----
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: 22 April 2002 14:39

|8.1.6 on NT
|The product that I support is still Rule based. I am planning to
bring it
|over to Cost based in the near future. What I wanted to do was to set
the
|init parameter to 'RULE' and then run statistics on the database. My
boss
|says we can't do this because "the execution plan was different for
the "set
|to rule and have statistics" vs. "set to choose and no statistics".
|I haven't heard this before - can anybody point me to the Fine Manual
to
|confirm or refute this. Perhaps this is another of those fine urban
legends?
|For the time being I am starting out with a small test database.
|--

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Author: Jonathan Lewis
  INET: jonathan_at_jlcomp.demon.co.uk

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