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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Mark Kirkwood <markir@paradise.net.nz>
Cc: Josh Berkus <josh@agliodbs.com>
Cc: Gavin Sherry <swm@linuxworld.com.au>
Cc: Jie Zhang <jzhang@greenplum.com>
Cc: pgsql-hackers@postgresql.org, Luke Lonergan <LLonergan@greenplum.com>
Subject: Re: On-disk bitmap index patch
Date: Thu, 27 Jul 2006 01:14:43 -0400
Message-ID: <29908.1153977283@sss.pgh.pa.us> (raw)
In-Reply-To: <44C81E32.8090500@paradise.net.nz>
References: <C0E1CD9D.8DC0%jzhang@greenplum.com>
	<Pine.LNX.4.58.0607240720180.19004@linuxworld.com.au>
	<28525.1153698215@sss.pgh.pa.us>
	<Pine.LNX.4.58.0607240952250.19854@linuxworld.com.au>
	<28750.1153700718@sss.pgh.pa.us>
	<44C6652C.1020203@agliodbs.com>
	<24309.1153860389@sss.pgh.pa.us>
	<44C6C8CB.9030802@paradise.net.nz>
	<1593.1153923961@sss.pgh.pa.us>
	<44C81E32.8090500@paradise.net.nz>

Mark Kirkwood <markir@paradise.net.nz> writes:
> An obvious deduction is that the TPCH dataset is much more amenable to 
> run compression than my synthetic Zipfian data was. The interesting 
> question is how well "real" datasets are run compressable,

Yeah --- the back-of-the-envelope calculations I was making presupposed
uniform random distribution, and we know that's often not realistic for
real datasets.  A nonuniform distribution would probably mean that some
of the bitmaps compress better-than-expected and others worse.  I have
no idea how to model that and guess what the overall result is ...

			regards, tom lane



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