Simon Riggs <si...@2ndquadrant.com> writes: > On Fri, 2008-12-12 at 11:16 -0500, Tom Lane wrote: >> Perhaps a better plan is to try to de-emphasize use of ndistinct, >> though I concede I have no idea how to do that.
> We don't actually care about the accuracy of the ndistinct much, just > the accuracy of our answer to the question "given work_mem = X, is it > better to use a hash plan". That's hardly the only thing we use ndistinct for. Also, it's a bit too simplistic to suppose that we only have to make the right binary choice between hash and something else at a particular plan level. If we don't have at least ballpark-correct figures for cost and number of output rows, we'll start making mistakes at higher plan levels. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers