Re: Optimizers

In <1993Aug16.233027.1_at_otago.ac.nz> is40511_at_otago.ac.nz writes:

>Hi,
> I just wanna' get something straight.
 

>There are 2 types of query optimizers, rule-based and cost-based.
>Rule-based optimizers have certain rules that they use to optimize the 'where'
>clauses.
>Cost-based uses statistics about tables (cardinality etc.) to optimize.
 

>Oracle V6. has a rule-based, but no cost-based optimizer.
>Oracle V7 has both, but there has been complaints of that the cost-based one is
>slow.

All of the above are true. But bear in mind that those users who run queries where the cost-based optimiser is faster have no reason to make a big noise about it.

>I'd be grateful if anyone could tell me whether, I'm right, wrong, in the
>ballpark ...

>Thanks,
> Rowan.

graeme

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