Re: Planner hints in Postgresql

On Mon, Mar 17, 2014 at 9:45 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> David Johnston <polobo(at)yahoo(dot)com> writes:
> > Need to discuss the general "why" before any meaningful help on the
> "how" is
> > going to be considered by hackers.
>
> Possibly worth noting is that in past discussions, we've concluded that
> the most sensible type of hint would not be "use this plan" at all, but
> "here's what to assume about the selectivity of this WHERE clause".
> That seems considerably less likely to break than any attempt to directly
> specify plan details.
>
>
Isnt using a user given value for selectivity a pretty risky situation as
it can horribly screw up the plan selection?

Why not allow the user to specify an alternate plan and have the planner
assign a higher preference to it during plan evaluation? This shall allow
us to still have a fair evaluation of all possible plans as we do right now
and yet have a higher preference for the user given plan during evaluation?

Regards,

Atri

--
Regards,

Atri
*l'apprenant*