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First, genericcostestimate() was being way too liberal about including partial-index conditions in its selectivity estimate, resulting in substantial underestimates for situations such as an indexqual "x = 42" used with an index on x "WHERE x >= 40 AND x < 50". While the code is intentionally set up to favor selecting partial indexes when available, this was too much... Second, choose_bitmap_and() was likewise easily fooled by cases of this type, since it would similarly think that the partial index had selectivity independent of the indexqual. Fixed by using predicate_implied_by() rather than simple equality checks to determine redundancy. This is a good deal more expensive but I don't see much alternative. At least the extra cost is only paid when there's actually a partial index under consideration. Per report from Jeff Davis. I'm not going to risk back-patching this, though. |
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