From: Martijn van Oosterhout <kleptog@svana.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Stephan Vollmer <svollmer@gmx.de>
Cc: pgsql-performance@postgreSQL.org
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
Date: Fri, 20 Jan 2006 23:33:27 +0100
Message-ID: <20060120223327.GH31908@svana.org> (raw)
In-Reply-To: <27264.1137793817@sss.pgh.pa.us>
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>
On Fri, Jan 20, 2006 at 04:50:17PM -0500, Tom Lane wrote:
> (hemdistcache calls hemdistsign --- I think gprof is doing something
> funny with tail-calls here, and showing hemdistsign as directly called
> from gtsvector_picksplit when control really arrives through hemdistcache.)
It may be the compiler. All these functions are declared static, which
gives the compiler quite a bit of leeway to rearrange code.
> The bulk of the problem is clearly in this loop, which performs O(N^2)
> comparisons to find the two entries that are furthest apart in hemdist
> terms:
Ah. A while ago someone came onto the list asking about bit strings
indexing[1]. If I'd known tsearch worked like this I would have pointed
him to it. Anyway, before he went off to implement it he mentioned
"Jarvis-Patrick clustering", whatever that means.
Probably more relevent was this thread[2] on -hackers a while back with
pseudo-code[3]. How well it works, I don't know, it worked for him
evidently, he went away happy...
[1] http://archives.postgresql.org/pgsql-general/2005-11/msg00473.php
[2] http://archives.postgresql.org/pgsql-hackers/2005-11/msg01067.php
[3] http://archives.postgresql.org/pgsql-hackers/2005-11/msg01069.php
Hope this helps,
--
Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.
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To: pgsql-performance@postgresql.org
Cc: kleptog@svana.org, tgl@sss.pgh.pa.us, svollmer@gmx.de
Subject: Re: [GENERAL] Creation of tsearch2 index is very slow
In-Reply-To: <20060120223327.GH31908@svana.org>
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