Re: MTS&Cost based Optimzer

On Tuesday 24 April 2001 06:15, Rachel Carmichael wrote:

>

LOL! Most of us here know this, but for the benefit of you that don't, here goes.

If your system is running fine on rule-based optimization, be *very* cautious about changing to cost-based.

Sure, cost-based has lots of bells and whistles, and allows some fine grained control through hints, and is required for certain operations.

But it can bite you when you aren't looking. One gotcha that comes to mind is that you will suddenly get hash joins performed on SQL where nested loops works just fine, and your app's will suddenly go very slowly.

Changing to cost-based requires some planning, testing and familiarization.

Don't just turn it on until you know what you are doing.

Jared

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