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Re: generalizing the planner knobs

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Neil Conway <neilc(at)samurai(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: generalizing the planner knobs
Date: 2005-12-01 16:49:42
Message-ID: 11805.1133455782@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Neil Conway <neilc(at)samurai(dot)com> writes:
> ... ISTM that a simple improvement to what we have now
> would allow for a wider range of planner hints with only minor changes:
> we could replace the enable_XXX variables with a set of variables that
> would add an arbitrary constant to the estimated cost of each type of
> query node. (Alternatively, an arbitrary multiplier could be specified;
> I'm not sure which would be better.)

I think the multiplier would be better, because it'd avoid the problem
you mention later that useful values would be dependent on the planner's
cost units.  Also, one could sanely allow a multiplier less than one,
so as to favor instead of penalize a particular plan type.

			regards, tom lane

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