Re: Multi-pass planner

On Friday, April 05, 2013 1:59 AM Robert Haas wrote:
> On Thu, Apr 4, 2013 at 2:53 PM, Dimitri Fontaine
> <dimitri(at)2ndquadrant(dot)fr> wrote:
> > Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> >> for estimate_worstcase_fraction. So, when computing the cost of a
> >> path, we'd compute our current expected-case estimate, and also a
> >> worst-case estimate, and then compute the final cost as:
> >
> > There also was the idea for the executor to be able to handle
> alternate
> > plans and some heuristic to determine that the actual cost of running
> a
> > plan is much higher than what's been estimated, so much so as to
> switch
> > to starting from scratch with the other plan instead.
>
> Yeah. The thing is, if the plan has any side effects, that's not
> really an option. And even if it doesn't, it may throw away a lot of
> work.

Why to throw away all the work, it could as well try to repair the plan or
even if plan repair is not possible, it can keep multiple plans and
next time can try to choose best among available one's.

With Regards,
Amit Kapila.