You
are pulling a fair amount of data from the database and doing a lot of
computation in the SQL. I'm not sure how fast this query could be expected
to run, but I had one idea. If you've
inserted and deleted a lot into this table, you will need to run vacuum
ocasionally. If you haven't been doing that, I would try a VACUUM FULL
ANALYZE on the table. (That will take a lock on the table and prevent
clients from reading data while it is running.)
-----Original Message-----Hi,
From: pgsql-performance-owner@xxxxxxxxxxxxxx [mailto:pgsql-performance-owner@xxxxxxxxxxxxxx] On Behalf Of gulsah
Sent: Friday, April 28, 2006 6:31 AM
To: pgsql-performance@xxxxxxxxxxxxxx
Subject: [PERFORM] query performance question
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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