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Re: Planner creating ineffective plans on LEFT OUTER joins

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Robert Haas" <robertmhaas(at)gmail(dot)com>
Cc: "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 05:23:18
Message-ID: 5446.1214457798@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
"Robert Haas" <robertmhaas(at)gmail(dot)com> writes:
> I can predict that Tom will say that the planning time it would take
> to avoid this problem isn't justified by the number of queries that it
> would improve.

Took the words right out of my mouth ;-)

It would be *possible* to do this sort of thing, but what it would
imply is re-planning entire join nests on the strength of assumptions
that some additional constraints are available.  Right now we only
do that for individual inner-side relations.  AFAICS extending that
to sub-joins would result in an exponential increase in plan time.

			regards, tom lane

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