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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: [PERFORM] Slow query: bitmap scan troubles
Date: Sun, 06 Jan 2013 18:17:23 -0500
Message-ID: <8803.1357514243@sss.pgh.pa.us> (raw)
In-Reply-To: <8539.1357513385@sss.pgh.pa.us>
References: <092a01cdd230$ff6143c0$fe23cb40$@foo.me.uk>
	<CAGTBQpaKOfZs+qy+S7CCPcTg7PYOrwgcQAXgWV88cQTn-BFstg@mail.gmail.com>
	<CAMkU=1wEc1cCeUdR1oZ3Q2fe2pGj6tvrwRcY2obbfEk8LcNypQ@mail.gmail.com>
	<097601cdd249$ae338530$0a9a8f90$@foo.me.uk>
	<CAMkU=1wmxKifgUufbSffQ+VH3kFNczK65MxXetwVFJZd3zvkeA@mail.gmail.com>
	<CAMkU=1w40aQt0twukCsvL2hPHUPujLqJBe8v90phuqBJ5wgw1Q@mail.gmail.com>
	<9022.1354730710@sss.pgh.pa.us>
	<CAMkU=1ykyMgXccv2dAWKOXdDx5U0Qpc28aW6k659hvE7VZEMXQ@mail.gmail.com>
	<28944.1357424296@sss.pgh.pa.us>
	<CA+U5nMLJBrnU+B6md5VR1GHGz6Ji5MEZd6QE+favQYLjv9H8JA@mail.gmail.com>
	<18164.1357498720@sss.pgh.pa.us>
	<CA+U5nMLjf2-kTa4-AR-0XLKKwbc+=_fb4237i_UAWYzowW+-1Q@mail.gmail.com>
	<8539.1357513385@sss.pgh.pa.us>
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I wrote:
> [ slightly bogus graph ]

Ooops, it seems the ^ operator doesn't do what I thought in gnuplot.
Here's a corrected version.

			regards, tom lane
set terminal png small color
set output 'new_fudge.png'
set xlabel "Index tuples"
set ylabel "Added cost"
set logscale x
set logscale y
h(x) = (x <= 256) ? 0.0001/0.005 : (x <= 256*256) ? (1./2)*log(x)/log(2) : (x <= 256*256*256) ? (2./3)*log(x)/log(2) : (x <= 256.0*256*256*256) ? (3./4)*log(x)/log(2) : (x <= 256.0*256*256*256*256) ? (4./5)*log(x)/log(2) : (5./6)*log(x)/log(2)
historical(x) = (4 * x/100000) < 100 ? 4 * x/100000 : 1/0
ninepoint2(x) = (4 * x/10000) < 100 ? 4 * x/10000 : 1/0
head(x) = 4*log(1 + x/10000)
plot [10:1e9] h(x)*0.005, 0.005 * log(x)/log(2), head(x), historical(x), ninepoint2(x)

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