Re: Oracle Cost-Based Optimizer

In article <30B4AC4D.5402_at_Bentley.nl>, Sybrand Bakker <Sybrand.Bakker_at_Bentley.nl> says:
>
>Some general remarks:
>First of all make sure you have updated statistics in your
>data-dictionary by issuing analyze table statements.
>Secondly, the cost-based optimizer reads from left to right instead of
>right to left. So
>from a,b,c
>will have table c driving in rule-based approach and table a driving
>in cost-based approach.
>Third, in general the cost-based optimizer produces incorrect results
>when small reference tables are included, that describes id's and so
>on. It has a preference to make those tables driving which is clearly
>silly.
>Fourth, don't forget cost-based optimizer tries to reduce I/O. In some
>cases I found out that joins by means of nested-loops actually used
>more I/O compared to merge joins. You should use tkprof to collect
>actual I/O statistics before starting to curse Oracle.
>Fifth, As a last resort you can always correct the query-plan by
>introducing hints in your statement.
>
>Sybrand Bakker
>Senior IS Analyst
>Bentley Systems Europe
>Hoofddorp
>The Netherlands
>
>#include <std_dclaimer.h>

Thanks for your advice. I will try them.

                                  Ja Uhm