Skip site navigation (1) Skip section navigation (2)

Re: Planner creating ineffective plans on LEFT OUTER joins

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Planner creating ineffective plans on LEFT OUTER joins
Date: 2008-06-26 21:23:18
Message-ID: 21375.1214515398@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com> writes:
> Couldn't the planner itself make a good guess if it should
> keep trying based on the estimated cost?

> if (the_best_plan_I_found_so_far_looks_like_itll_take_an_hour)
>    keep_optimizing_for_a_few_minutes
> if (the_best_plan_I_found_so_far_looks_like_itll_take_0.01ms)
>    stop_planning_and_run_with_it

You're operating on a mistaken assumption, which is that we generate a
complete plan and then generate another.  The places where we'd actually
be doing something with an effort variable are usually dealing with
small parts of plans, or even with preparatory calculations before we've
got anything plan-like at all.  They haven't got a sufficiently holistic
view of what's happening to apply a rule like the above.

			regards, tom lane

In response to

Responses

pgsql-hackers by date

Next:From: Ron MayerDate: 2008-06-26 21:33:48
Subject: Re: Planner creating ineffective plans on LEFT OUTER joins
Previous:From: Dickson S. GuedesDate: 2008-06-26 21:18:47
Subject: Re: TODO Item: Allow pg_hba.conf to specify host names along with IP addresses

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group