732bfa2448
cost_index's method for estimating per-tuple costs of evaluating filter conditions (a/k/a qpquals) was completely wrong in the presence of derived indexable conditions, such as range conditions derived from a LIKE clause. This was largely masked in common cases as a result of all simple operator clauses having about the same costs, but it could show up in a big way when dealing with functional indexes containing expensive functions, as seen for example in bug #6579 from Istvan Endredy. Rejigger the calculation to give sane answers when the indexquals aren't a subset of the baserestrictinfo list. As a side benefit, we now do the calculation properly for cases involving join clauses (ie, parameterized indexscans), which we always overestimated before. There are still cases where this is an oversimplification, such as clauses that can be dropped because they are implied by a partial index's predicate. But we've never accounted for that in cost estimates before, and I'm not convinced it's worth the cycles to try to do so.
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