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From: Steinar H. Gunderson <sgunderson@bigfoot.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org, Teodor Sigaev <teodor@sigaev.ru>
Cc: Oleg Bartunov <oleg@sai.msu.su>
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
Date: Sat, 21 Jan 2006 01:36:46 +0100
Message-ID: <20060121003646.GA31406@uio.no> (raw)
In-Reply-To: <6743.1137802990@sss.pgh.pa.us>
References: <26583.1137788505@sss.pgh.pa.us>
	<20060120205132.GF31908@svana.org>
	<26958.1137791955@sss.pgh.pa.us>
	<20060120213754.GG31908@svana.org>
	<7.0.1.0.2.20060120174141.039b03e8@earthlink.net>
	<6111.1137797436@sss.pgh.pa.us>
	<20060120225751.GA27230@uio.no>
	<6532.1137801157@sss.pgh.pa.us>
	<20060121000519.GA29755@uio.no>
	<6743.1137802990@sss.pgh.pa.us>

On Fri, Jan 20, 2006 at 07:23:10PM -0500, Tom Lane wrote:
> I'm not very clear on what tsearch2 is doing with these bitmaps, but it
> looks like an upper page's downlink has the union (bitwise OR) of the
> one-bits in the values on the lower page, and you have to visit the lower
> page if this union has a nonempty intersection with the set you are looking
> for.  If that's correct, what you really want is to divide the values so
> that the unions of the two sets have minimal overlap ... which seems to me
> to have little to do with what the code does at present.

Sort of like the vertex-cover problem? That's probably a lot harder than
finding the two farthest points...

/* Steinar */
-- 
Homepage: http://www.sesse.net/

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