Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> In general, I think it'd be naive that we can make planner smarter with
> no extra overhead spent on planning, and we can never accept patches
> adding even tiny overhead. With that approach we'd probably end up with
> a trivial planner that generates just a single query plan, because
> that's going to be the fastest planner. A realistic approach needs to
> consider both the planning and execution phase, and benefits of this
> patch seem to be clear - if you have queries that do benefit from it.
I think that's kind of attacking a straw man, though. The thing that
people push back on, or should push back on IMO, is when a proposed
patch adds significant slowdown to queries that it has no or very little
hope of improving. The trick is to do expensive stuff only when
there's a good chance of getting a better plan out of it.
regards, tom lane