Atri Sharma wrote > On Mon, Mar 17, 2014 at 9:45 PM, Tom Lane < > tgl@.pa
> > wrote: > >> David Johnston < > polobo@ > > 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? The larger question to answer first is whether we want to implement something that is deterministic... How about just dropping the whole concept of "hinting" and provide a way for someone to say "use this plan, or die trying." Maybe require it be used in conjunction with named PREPAREd statements: PREPARE s1 (USING /path/to/plan_def_on_server_or_something_similar) AS SELECT ...; Aside from whole-plan specification I can definitely see where join/where specification could be useful if it can overcome the current limitation of not being able to calculate inter-table estimations. David J. -- View this message in context: http://postgresql.1045698.n5.nabble.com/Planner-hints-in-Postgresql-tp5796347p5796378.html Sent from the PostgreSQL - hackers mailing list archive at Nabble.com. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers