Re: Cost-based optimizers

> I saw it in print; the only thing that seemed interesting about it was
> the recommendation that query optimization be biased towards the
> notion of "stable plans," query plans that may not be the most
> "aggressively fast," but which don't fall apart into hideous
> performance if the estimates are a little bit off.

And the answer is interesting as well:

"I think we have to approach it in two ways. One is that you have to be
able to execute good plans, and during the execution of a plan you want
to notice when the actual data is deviating dramatically from what you
expected. If you expected five rows and you’ve got a million, chances
are your plan is not going to do well because you chose it based on the
assumption of five. Thus, being able to correct mid-course is an area of
enhancement for query optimizers that IBM is pursuing."

Hmmm dynamic re-planning!

Chris