To: Craig James <craig_james@emolecules.com>
cc: valiouk@yahoo.co.uk, psql performance <pgsql-performance@postgresql.org>
Subject: Re: Perl/DBI vs Native 
In-reply-to: <4884C633.5050506@emolecules.com> 
References: <768129.60859.qm@web25802.mail.ukl.yahoo.com>
	<4884C633.5050506@emolecules.com>
Comments: In-reply-to Craig James <craig_james@emolecules.com>
	message dated "Mon, 21 Jul 2008 10:24:03 -0700"
Date: Mon, 21 Jul 2008 14:44:32 -0400
Message-ID: <16163.1216665872@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Craig James <craig_james@emolecules.com> writes:
> Valentin Bogdanov wrote: 
>> I have ran quite a few tests comparing how long a query takes to
>> execute from Perl/DBI as compared to psql/pqlib. No matter how many
>> times I run the test the results were always the same.
>> 
>> I run a SELECT all on a fairly big table and enabled the
>> log_min_duration_statement option. With psql postgres consistently
>> logs half a second while the exact same query executed with Perl/DBI
>> takes again consistently 2 seconds.

> The problem may be that your two tests are not equivalent.  When Perl
> executes a statement, it copies the *entire* result set back to the
> client before it returns the first row.

Sure, but so does psql (unless you've turned on the magic FETCH_COUNT
setting).  I think the theories about prepared versus literal statements
were more promising; but I don't know DBI well enough to know exactly
what it was sending to the server.

			regards, tom lane