From: Ron Mayer <rm_pg@cheapcomplexdevices.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: On-disk bitmap index patch
Date: Tue, 25 Jul 2006 14:53:29 -0700
Message-ID: <44C692D9.3050406@cheapcomplexdevices.com> (raw)
In-Reply-To: <5085.1153802202@sss.pgh.pa.us>
References: <C0EAB84F.8FB4%jzhang@greenplum.com>
<200607250104.k6P14St25388@momjian.us>
<20060725015805.GA30087@mark.mielke.cc>
<5085.1153802202@sss.pgh.pa.us>
Tom Lane wrote:
> mark@mark.mielke.cc writes:
>> Reading 1/4, for a larger table, has a good chance of being faster than
>> reading 4/4 of the table. :-)
>
> Really?
>
> If you have to hit one tuple out of four, it's pretty much guaranteed
> that you will need to fetch every heap page.
I think it's not uncommon to have data that is more clustered than expected.
In my case it shows up often in GIS data; where often a query
that only accesses 1/4 of the rows in the table really will
only access about 1/4 of the pages in the table -- for example
when analyzing Texas or the Southwest US.
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To: pgsql-hackers@postgresql.org
Cc: rm_pg@cheapcomplexdevices.com, tgl@sss.pgh.pa.us
Subject: Re: On-disk bitmap index patch
In-Reply-To: <44C692D9.3050406@cheapcomplexdevices.com>
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