## query performance question

From: gulsah pgsql-performance(at)postgresql(dot)org query performance question 2006-04-28 11:30:59 20060428113059.57107.qmail@web51009.mail.yahoo.com (view raw, whole thread or download thread mbox) 2006-04-28 11:30:59 from gulsah  2006-05-01 00:36:11 from "Dave Dutcher" pgsql-performance
```Hi,

I have a performance problem with Postgresql version 8.1 installed on a Fedora Core release 4 (Stentz) with kernel version 2.6.11.

The machine I am working on has 512MB of RAM and Pentium III 800 MHz CPU.

I have only one table in the database which consists of 256 columns and 10000 rows. Each column is of float type and each row corresponds to a vector in my application. What I want to do is to compute the distance between a predefined vector in hand and the ones in the database.

The computation proceeds according to the following pseudocode:

for(i=1; i<=256 ; i++){
distance += abs(x1_i - x2_i);
}

where x1_i denotes the vector in hand's i coordinate and x2_i denotes the i
coordinate of the vector in the database.

The distance computation have to be done for all the vectors in the database
by means of a query and the result set should be sorted in terms of the
computed distances.

When I implement the query and measure the time spent for it in an application
I see that the query is handled in more than 8 seconds which is undesirable in
my application.

Here what I want to ask you all is that, is it a normal performance for a
computer with the properties that I have mentioned above? Is there any solution
in your mind to increase the performance of my query?

To make it more undestandable, I should give the query for vectors with size
3, but in my case their size is 256.

select
id as vectorid,
abs(40.9546-x2_1)+abs(-72.9964-x2_2)+abs(53.5348-x2_3) as distance
from vectordb
order by distance

Thank you all for your help.

-
gulsah

---------------------------------
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