To: "tschak" <jochen.schlosser@gmail.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Index occupancy 
In-reply-to: <1138888981.186497.321210@z14g2000cwz.googlegroups.com> 
References: <1138888981.186497.321210@z14g2000cwz.googlegroups.com>
Comments: In-reply-to "tschak" <jochen.schlosser@gmail.com>
	message dated "02 Feb 2006 06:03:01 -0800"
Date: Sat, 04 Feb 2006 19:49:05 -0500
Message-ID: <5056.1139100545@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"tschak" <jochen.schlosser@gmail.com> writes:
> I have a question concerning the size of an index...
> What I acually did was bulid a btree index on an smallint attribute
> within a table with 10^8 rows. The table itself is app. 10GB large and
> what I would like to have the smallest possible indeces. Unfortunately
> the current size is about 2GB per indexed column (8 columns are indexed
> in total) which is too large if the planner is supposed to choose a
> bitmap scan between all of the indices.

> So what I would like to know is the following:
> Is there an easy way to tell postgres to occupy the index pages up to
> 100 %?

No, but even if there were it wouldn't make much of a difference.  The
minimum possible size of a PG index is about 16 bytes per entry, which
would still put you at 1.6Gb for that many rows.

			regards, tom lane