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Re: GEQO: ERX

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tobias Zahn <tobias-zahn(at)arcor(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: GEQO: ERX
Date: 2009-05-02 15:37:16
Message-ID: 15658.1241278636@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Tobias Zahn <tobias-zahn(at)arcor(dot)de> writes:
> I didn't not get any response to my initial message below. Now I am
> wondering if nobody is into the optimizer or if my question was just too
> stupid. Could you please give me some clues? Your help would really be
> appreciated.

Well, nobody's into GEQO very much.  I took a quick look and didn't
think that deleting the ERX support would save anything noticeable,
but you're welcome to try it if you think different.

The real problem with working on GEQO, in my humble opinion, is that
it's throwing good effort after bad.  That module doesn't need marginal
fixing, it needs throwing away and rewriting from scratch.  Bad enough
that it's convoluted and full of dead (experimental?) code; but I don't
even believe that it's based on a good analogy.   The planning problem
is not all that much like traveling salesman problems, so heuristics
designed for TSP are of pretty questionable usefulness to start with.
That complaint could have been refuted if the module performed well,
but in fact if you check the archives you'll find many many complaints
about it --- its ability to find good plans seems to be mostly dependent
on luck.

My knowledge of AI search algorithms is about 20 years obsolete, but
last I heard simulated annealing had overtaken genetic algorithms for
many purposes.  It might be interesting to try a rewrite based on SA;
or maybe there's something better out there now.

			regards, tom lane

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Subject: Re: GEQO: ERX
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