Peter Eisentraut wrote: > > mlw writes: > > > Adding huristics, such as weighting for index scans, is not making the planner > > stupider. It is making it smarter and more flexable. > > If life was as simple as index or no index then this might make some > sense. But in general the planner has a whole bunch of choices of join > plans, sorts, scans, and the cost of an individual index scan is hidden > down somewhere in the leaf nodes, so you can't simply say that plans of > type X should be preferred when the cost estimates are close. > No doubt, no one is arguing that it is easy, but as I said in a branch of this discussion, when the planner has multiple choices, and the cost ranges overlapp, the relative numbers are not so meaningful that huristics would not improve the algorithm.
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