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Re: Bitmap index status

From: Mark Wong <markw(at)osdl(dot)org>
To: Luke Lonergan <llonergan(at)greenplum(dot)com>
Cc: Jie Zhang <jzhang(at)greenplum(dot)com>, Ayush Parashar <aparashar(at)greenplum(dot)com>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, swm(at)linuxworld(dot)com(dot)au, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Bitmap index status
Date: 2006-09-28 16:50:14
Message-ID: 451BFD46.8090404@osdl.org (view raw or flat)
Thread:
Lists: pgsql-hackers
Luke Lonergan wrote:
> Mark,
> 
> On 9/25/06 11:32 AM, "Mark Wong" <markw(at)osdl(dot)org> wrote:
> 
>> Yeah, basically gather as many stats as I can to accurately profile the
>> overall system performance.  I thought it would be appropriate to use a
>> TPC-H based workload as one measuring stick to use for bitmap indexes.
> 
> Note that the TPC-H queries don't follow the typical good use case for
> bitmap indexes.  You'd like to see queries that use multiple AND and OR
> clauses, otherwise there may be no benefit.

Oh right, people keep telling me that and it keeps going in one ear and 
out the other...

> Also, DBT-3/TPC-H on Postgres right now does not benefit from indices
> overall.  The planner has limitations WRT selectivity estimates and other
> limitations that cause it to choose index access poorly for the query
> workload.  We have two new features coming (for 8.3) that fix this, but for
> now we find that indexes are a net loss, in some queries a huge loss.

Great, I'll keep my eye for those. :)

> If you look at the whitepaper that Ayush Parashar published, he uses the
> TPC-H data with some targeted queries that showcase the best use-cases for
> bitmap index.

Mark

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