Re: Slow concurrent update of same row in a given table

On Thu, Sep 29, 2005 at 07:59:34AM +0530, Rajesh Kumar Mallah wrote:
> > I see. These problems regularly come up in database design. The best thing
> > you can do is modify your database design/application such that instead of
> > incrementing a count in a single row, you insert a row into a table,
> > recording the 'dispatch_id'. Counting the number of rows for a given
> > dispatch id will give you your count.
> >
>
> sorry i will be accumulating huge amount of rows in seperate table
> with no extra info when i really want just the count. Do you have
> a better database design in mind?
>
> Also i encounter same problem in implementing read count of
> articles in sites and in counting banner impressions where same
> row get updated by multiple processes frequently.

Databases like to work on *sets* of data, not individual rows. Something
like this would probably perform much better than what you've got now,
and would prevent having a huge table laying around:

INSERT INTO holding_table ... -- Done for every incomming
connection/what-have-you

CREATE OR REPLACE FUNCTION summarize() RETURNS void AS $$
DECLARE
    v_rows int;
BEGIN
    DELETE FROM holding_table;
    GET DIAGNOSTICS v_rows = ROW_COUNT;
    UPDATE count_table
        SET count = count + v_rows
    ;
END;
$$ LANGUAGE plpgsql;

Periodically (say, once a minute):
SELECT summarize()
VACUUM holding_table;
VACUUM count_table;
--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461