Re: Multi-pass planner

Robert Haas <robertmhaas@gmail.com> wrote:
> I think one of the problems with the planner is that all decisions
> are made on the basis of cost.  Honestly, it works amazingly well in
> a wide variety of situations, but it can't handle things like "we
> might as well materialize here, because it doesn't cost much and
> there's a big upside if our estimates are off".  The estimates are
> the world, and you live and die by them.
["thinking out loud"]
If there were some reasonable way to come up with a *range* for cost
at each step, a reasonable heuristic might be to cost the plan using
minimum values and maximum values, and use the root mean square of the
two for comparisons to other plans.  I don't know that we have a good
basis to come up with ranges rather than absolute numbers, though.
-Kevin