Re: query plan

a.) If statistics are available it will use the cost based optimizer otherwise it will use the rule based optimizer. b) No. It's impossible. It just does its best based on the information it has.
c) The plan doesn't fail. All of its solutions are valid as far as the results are concerned, they just perform at different rates. d) Yes. Use hints or the rule based optimizer.

Cost based is best for adhoc type queries. Rule base is best for large optimized queries. Cost based plus hints is probably the best of both worlds.

Naushi Hussain wrote:

> I am trying to understand what goes on behind the screen when a query is
> issued.
>
> a.Does oracle optimizer gets the best plan and execute it based on
> statistics available.
> b.does it always comes up with the best plan
> c. does the plan ever fail and if it does under what circumstances- then
> the query times out?
> d. can we override the optimizer plan and how
>
> any help will be appreciated.
Received on Tue Feb 09 1999 - 03:04:13 CST