On Mon, Mar 17, 2014 at 7:01 PM, Jim Nasby <jim@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.
