From: Tom Lane <tgl@sss.pgh.pa.us>
To: 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: Sun, 23 Jul 2006 20:25:18 -0400
Message-ID: <28750.1153700718@sss.pgh.pa.us> (raw)
In-Reply-To: <Pine.LNX.4.58.0607240952250.19854@linuxworld.com.au>
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>
Gavin Sherry <swm@linuxworld.com.au> writes:
> On Sun, 23 Jul 2006, Tom Lane wrote:
>> However, the main problem I've got with this is that a new index AM is a
>> pretty large burden, and no one's made the slightest effort to sell
>> pghackers on taking this on.
> For low cardinality sets, bitmaps greatly out perform btree.
If the column is sufficiently low cardinality, you might as well just do
a seqscan --- you'll be hitting most of the heap's pages anyway. I'm
still waiting to be convinced that there's a sweet spot wide enough to
justify supporting another index AM. (I'm also wondering whether this
doesn't overlap the use-case for GIN.)
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, swm@linuxworld.com.au, jzhang@greenplum.com, LLonergan@greenplum.com
Subject: Re: On-disk bitmap index patch
In-Reply-To: <28750.1153700718@sss.pgh.pa.us>
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