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Re: [INTERFACES] Re: [HACKERS] changes in 6.4

From: Sbragion Denis <infotecn(at)tin(dot)it>
To: David Hartwig <daybee(at)bellatlantic(dot)net>, Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>
Cc: hannu(at)trust(dot)ee, pgsql-interfaces(at)postgreSQL(dot)org, hackers(at)postgreSQL(dot)org
Subject: Re: [INTERFACES] Re: [HACKERS] changes in 6.4
Date: 1998-08-31 06:53:12
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-generalpgsql-hackerspgsql-interfaces

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 !


	Dr. Sbragion Denis
	Tel, Fax: +39 39 2324054

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