On Thu, 2006-03-16 at 00:07 +0000, Simon Riggs wrote: > On Wed, 2006-03-15 at 14:17 -0500, Tom Lane wrote: > > > It looks to me like this is a matter of bad cost estimation, ie, it's > > thinking the other index is cheaper to use. Why that is is not clear. > > Can we see the pg_stats rows for ctofcNo and calDate? > > ISTM that when the BETWEEN constants match we end up in this part of > clauselist_selectivity()... (and now for the whole email...) /* * It's just roundoff error; use a small positive * value */ s2 = 1.0e-10; so that the planner underestimates the cost of using "Cal_CalDate" so that it ends up the same as "Cal_CtofcNo", and then we pick "Cal_CalDate" because it was created first. Using 1.0e-10 isn't very useful... the selectivity for a range should never be less than the selectivity for an equality, so we should simply put in a test against one of the pseudo constants and use that as the minimal value. That should lead to raising the apparent cost of Cal_CalDate so that Cal_CtofcNo can take precedence. Best Regards, Simon Riggs
