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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Ron <rjpeace@earthlink.net>
Cc: Martijn van Oosterhout <kleptog@svana.org>
Cc: pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
Date: Fri, 20 Jan 2006 17:50:36 -0500
Message-ID: <6111.1137797436@sss.pgh.pa.us> (raw)
In-Reply-To: <7.0.1.0.2.20060120174141.039b03e8@earthlink.net>
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>
	<7.0.1.0.2.20060120174141.039b03e8@earthlink.net>

Ron <rjpeace@earthlink.net> writes:
> For an even more extreme speedup, don't most modern CPUs have an asm 
> instruction that counts the bits (un)set (AKA "population counting") 
> in various size entities (4b, 8b, 16b, 32b, 64b, and 128b for 64b 
> CPUs with SWAR instructions)?

Yeah, but fetching from a small constant table is pretty quick too;
I doubt it's worth getting involved in machine-specific assembly code
for this.  I'm much more interested in the idea of improving the
furthest-distance algorithm in gtsvector_picksplit --- if we can do
that, it'll probably drop the distance calculation down to the point
where it's not really worth the trouble to assembly-code it.

			regards, tom lane



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