On Tue, Oct 11, 2022 at 09:59:43AM -0400, Tom Lane wrote: > 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. We do have a correlation statistics value for each column but I am unclear if that would help here. -- Bruce Momjian <bruce@xxxxxxxxxx> https://momjian.us EDB https://enterprisedb.com Indecision is a decision. Inaction is an action. Mark Batterson
