On Mon, Mar 17, 2014 at 9:45 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> David Johnston <pol...@yahoo.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*
