Re: Planner hints in Postgresql

Claudio Freire <klaussfreire@gmail.com> writes:
> 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.

Yeah.  I would like to see the planner's cost estimates extended to
include some sort of uncertainty estimate, whereupon risk-averse people
could ask it to prefer low-uncertainty plans over high-uncertainty ones
(the plans we typically choose for ORDER BY ... LIMIT queries being great
examples of the latter).  But it's a long way from wishing that to making
it so.  Right now it's not even clear (to me anyway) how we'd measure or
model such uncertainty.
        regards, tom lane