David Rowley <dgrowleyml@xxxxxxxxx> writes: > It feels like something is a bit lacking in our cost model here. I'm > just not sure what that is. The example you show is the same old problem that we've understood for decades: for cost-estimation purposes, we assume that matching rows are more or less evenly distributed in the table. Their actual location doesn't matter that much if you're scanning the whole table; but if you're hoping that a LIMIT will be able to stop after scanning just a few rows, it does matter. While it'd be pretty easy to insert some ad-hoc penalty into the LIMIT estimation to reduce the chance of being fooled this way, that would also discourage us from using fast-start plans when they *do* help. So I don't see any easy fix. regards, tom lane
