Date: Sat, 21 Apr 2007 11:42:35 +1200
From: Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: index structure for 114-dimension vector
In-reply-to: <1177105284.28383.31.camel@dogma.v10.wvs>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Andrew Lazarus <andrew@pillette.com>, pgsql-performance@postgresql.org
Message-id: <46294FEB.9010909@paradise.net.nz>
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Jeff Davis wrote:
> On Fri, 2007-04-20 at 12:07 -0700, Andrew Lazarus wrote:
>> I have a table with 2.5 million real[] arrays. (They are points in a
>> time series.) Given a new array X, I'd like to find, say, the 25
>> closest to X in some sense--for simplification, let's just say in the
>> usual vector norm. Speed is critical here, and everything I have tried
>> has been too slow.
>>
>> I imported the cube contrib package, and I tried creating an index on
>> a cube of the last 6 elements, which are the most important. Then I
> 
> Have you tried just making normal indexes on each of the last 6 elements
> and see if postgresql will use a BitmapAnd to combine them? 
> 
>

I don't think that will work for the vector norm i.e:

|x - y| = sqrt(sum over j ((x[j] - y[j])^2))


Cheers

Mark