Message-Id: <3.0.5.32.19980831085312.00986cc0@MBox.InfoTecna.com>
Date: Mon, 31 Aug 1998 08:53:12 +0200
To: David Hartwig <daybee@bellatlantic.net>,
	Bruce Momjian <maillist@candle.pha.pa.us>
From: Sbragion Denis <infotecn@tin.it>
Subject: Re: [INTERFACES] Re: [HACKERS] changes in 6.4
Cc: hannu@trust.ee, pgsql-interfaces@postgreSQL.org, hackers@postgreSQL.org
In-Reply-To: <35E9726E.C6E73049@bellatlantic.net>
References: <199808290344.XAA28089@candle.pha.pa.us>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"

Hello,

At 11.40 30/08/98 -0400, David Hartwig wrote:
>> Why is the system cnf'ifying the query.  Because it  wants to have a
>> list of qualifications that are AND'ed, so it can just pick the most
>> restrictive/cheapest, and evaluate that one first.

Just a small question about all this optimizations stuff. I'm not a
database expert but I think we are talking about a NP-complete problem.
Could'nt we convert this optimization problem into another NP one that is
known to have a good solution ? For example for the traveling salesman
problem there's an alghoritm that provide a solution that's never more than
two times the optimal one an provides results that are *really* near the
optimal one most of the times. The simplex alghoritm may be another
example. I think that this kind of alghoritm would be better than a
collection ot tricks for special cases, and this tricks could be used
anyway when special cases are detected. Furthermore I also know that exists
a free program I used in the past that provides this kind of optimizations
for chip design. I don't remember the exact name of the program but I
remember it came from Berkeley university. Of course may be I'm totally
missing the point.

Hope it helps !

Bye!

	Dr. Sbragion Denis
	InfoTecna
	Tel, Fax: +39 39 2324054
	URL: http://space.tin.it/internet/dsbragio