To: Ivan Voras <ivoras@fer.hr>
Cc: pgsql-performance@postgresql.org
Subject: Re: Bitmasks
References: <439B0C9A.6010109@fer.hr>
In-Reply-To: <439B0C9A.6010109@fer.hr>
From: Greg Stark <gsstark@mit.edu>
Organization: The Emacs Conspiracy; member since 1992
Date: 11 Dec 2005 01:12:08 -0500
Message-ID: <87oe3of9hj.fsf@stark.xeocode.com>
Lines: 21
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Ivan Voras <ivoras@fer.hr> writes:

> select * from tt where (flags & 16) != 0;
> 
> I suspected radix trees could be used for this but it seems it doesn't work
> that way.

You would need a gist index method to make this work. I actually worked on one
for a while and had it working. But it wasn't really finished. If there's
interest I could finish it up and put it up somewhere like pgfoundry.

> If not, is there a way of quickly filtering by such "elements of a set" that
> doesn't involve creating 32 boolean fields (which would also need to be pretty
> uselessly indexed separately)?

You could create 32 partial indexes on some other column which wouldn't really
take much more space than a single index on that other column. But that won't
let you combine them effectively as a gist index would.

-- 
greg