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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dann Corbit <DCorbit@connx.com>
Cc: Alvaro Herrera <alvherre@commandprompt.com>
Cc: pgsql-hackers@postgresql.org, "PostgreSQL Performance" <pgsql-performance@postgresql.org>
Cc: Steve <cheetah@tanabi.org>
Subject: Re: [HACKERS] choose_bitmap_and again (was Re: Strangely Variable Query Performance)
Date: Sat, 14 Apr 2007 11:52:45 -0400
Message-ID: <4535.1176565965@sss.pgh.pa.us> (raw)
In-Reply-To: <D425483C2C5C9F49B5B7A41F89441547010005E0@postal.corporate.connx.com>
References: <Pine.GSO.4.64.0704121855300.17955@kittyhawk.tanabi.org>
	<10117.1176420763@sss.pgh.pa.us>
	<Pine.GSO.4.64.0704121928440.17955@kittyhawk.tanabi.org>
	<10355.1176422445@sss.pgh.pa.us>
	<Pine.GSO.4.64.0704122001160.17955@kittyhawk.tanabi.org>
	<10503.1176423606@sss.pgh.pa.us>
	<Pine.GSO.4.64.0704122025450.17955@kittyhawk.tanabi.org>
	<12360.1176436194@sss.pgh.pa.us>
	<Pine.GSO.4.64.0704122354430.17955@kit!tyhawk.tanabi.org>
	<26399.1176504501@sss.pgh.pa.us>
	<20070413232409.GI27255@alvh.no-ip.org>
	<D425483C2C5C9F49B5B7A41F89441547010005E0@postal.corporate.connx.com>

"Dann Corbit" <DCorbit@connx.com> writes:
> Instead of sorting, I suggest the quickselect() algorithm, which is
> O(n).

What for?  Common cases have less than half a dozen entries.  That is
not the place we need to be spending engineering effort --- what we
need to worry about is what's the choice algorithm, not implementation
details.

			regards, tom lane



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