"Kevin Grittner" <Kevin.Grittner@xxxxxxxxxxxx> writes: > The point I'm trying to make is that at planning time the > pg_statistic row for this "Charge"."reopHistSeqNo" column showed > stanullfrac as 0.989; it doesn't seem to have taken this into account > when making its guess about how many rows would be joined when it was > compared to the primary key column of the "CaseHist" table. It certainly does take nulls into account, but the estimate of resulting rows was still nonzero; and even if it were zero, I'd be very hesitant to make it choose a plan that is fast only if there were exactly zero such rows and is slow otherwise. Most of the complaints we've had about issues of this sort involve the opposite problem, ie, the planner is choosing a plan that works well for few rows but falls down because reality involves many rows. "Fast-for-few-rows" plans are usually a lot more brittle than the alternatives in terms of the penalty you pay for too many rows, and so putting a thumb on the scales to push it towards a "fast" corner case sounds pretty unsafe to me. As Simon notes, the only technically sound way to handle this would involve run-time plan changeover, which is something we're not nearly ready to tackle. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
