On Mon, Mar 17, 2014 at 7:01 PM, Jim Nasby <j...@nasby.net> wrote: > Even better would be if the planner could estimate how bad a plan will > become if we made assumptions that turn out to be wrong. >
That's precisely what risk estimation was about. Something like SELECT * FROM wherever WHEN id > something LIMIT COST 10000; Would forbid a sequential scan *if* the table is big enough to suspect the plan might take that much, or a nested loop *if* the planner cannot *prove* it will be faster than that. I don't believe the limit unit is obscure at all (page fetches being a nice measuring stick), but what is, is what do you do when no plan fits the limits.
