Commit b989619

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Fix cost estimation for indexscans on expensive indexed expressions.

genericcostestimate() and friends used the cost of the entire indexqual expressions as the charge for initial evaluation of indexscan arguments. But of course the index column is not evaluated, only the other side of the qual expression, so this was a bad overestimate if the index column was an expensive expression. To fix, refactor the logic in this area so that there's a single routine charged with deconstructing index quals and figuring out what is the index column and what is the comparison expression. This is more or less free in the case of btree indexes, since btcostestimate() was doing equivalent deconstruction already. It probably adds a bit of new overhead in the cases of other index types, but not a lot. (In the case of GIN I think I saved something by getting rid of code that wasn't aware that the index column associations were already available "for free".) Per recent gripe from Jeff Janes. Arguably this is a bug fix, but I'm hesitant to back-patch because of the possibility of destabilizing plan choices that people may be happy with.

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src/backend/utils/adt
- selfuncs.c

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pFad - (p)hone/(F)rame/(a)nonymizer/(d)eclutterfier! Saves Data!