Message-ID: <4BFE90B2.2050604@postnewspapers.com.au>
Date: Thu, 27 May 2010 23:33:06 +0800
From: Craig Ringer <craig@postnewspapers.com.au>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB;
	rv:1.9.1.9) Gecko/20100317 Thunderbird/3.0.4
MIME-Version: 1.0
To: Tyler Hildebrandt <tyler@campbell-lange.net>
CC: pgsql-performance@postgresql.org,
	Sebastian Ritter <sebastian@campbell-lange.net>,
	rory <rory@campbell-lange.net>
Subject: Re: Query timing increased from 3s to 55s when used as
	function	instead of select
References: <20100521135415.GA3445@campbell-lange.net>
In-Reply-To: <20100521135415.GA3445@campbell-lange.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

On 21/05/2010 9:54 PM, Tyler Hildebrandt wrote:
> We're using a function that when run as a select statement outside of the
> function takes roughly 1.5s to complete whereas running an identical
> query within a function is taking around 55s to complete.
>
> We are lost as to why placing this query within a function as opposed to
> substituting the variables in a select statement is so drastically different.

This is a frequently asked question. It's the same issue as with 
prepared queries, where the planner has to pick a more general plan when 
it doesn't know the value of a parameter. The short answer is "work 
around it by using EXECUTE ... USING to invoke your query dynamically".

( Oddly, this FAQ doesn't seem to be on the FAQ list at 
http://wiki.postgresql.org/wiki/FAQ )

--
Craig Ringer