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From: Ron <rjpeace@earthlink.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-performance@postgresql.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
Date: Fri, 20 Jan 2006 17:29:46 -0500
Message-ID: <7.0.1.0.2.20060120172335.039f5e20@earthlink.net> (raw)
In-Reply-To: <20060120221655.GA22581@uio.no>
References: <43D0ED57.1020608@gmx.de>
	<17454.1137771321@sss.pgh.pa.us>
	<20060120170452.GC31908@svana.org>
	<26153.1137784469@sss.pgh.pa.us>
	<20060120201036.GE31908@svana.org>
	<26583.1137788505@sss.pgh.pa.us>
	<20060120205132.GF31908@svana.org>
	<26958.1137791955@sss.pgh.pa.us>
	<20060120213754.GG31908@svana.org>
	<27264.1137793817@sss.pgh.pa.us>
	<20060120221655.GA22581@uio.no>

At 05:16 PM 1/20/2006, Steinar H. Gunderson wrote:
>On Fri, Jan 20, 2006 at 04:50:17PM -0500, Tom Lane wrote:
> > I wonder if there is a way to improve on that.
>
>Ooh, the farthest pair problem (in an N-dimensional vector space, though).
>I'm pretty sure problems like this has been studied quite extensively in the
>literature, although perhaps not with the same norm. It's known under both
>"farthest pair" and "diameter", and probably others. I'm fairly sure it
>should be solvable in at least O(n log n).

If the N-dimensional space is Euclidean (any <x, x+1> is the same 
distance apart in dimension x), then finding the farthest pair can be 
done in at least O(n).

If you do not want the actual distance and can create the proper data 
structures, particularly if you can update them incrementally as you 
generate pairs, it is often possible to solve this problem in O(lg n) or O(1).

I'll do some grinding.
Ron 





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  Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
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