Oracle 10 optimizer from RULE to COST: why?

Question

Oracle decided to dismiss the rule-based optimizer from version 10g, leaving the cost-based one as the only choice.

I think that a rule-based optimizer has the unv

Answer 1

The RBO is often predicatably bad as well as predictably good. It also doesn't support partitioning and some other database features. The CBO is much better, and as Quassnoi says plan stability is a feature of the CBO also.