Message-ID: <4BFE95E1.4070701@postnewspapers.com.au>
Date: Thu, 27 May 2010 23:55:13 +0800
From: Craig Ringer <craig@postnewspapers.com.au>
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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>
	<4BFE90B2.2050604@postnewspapers.com.au>
In-Reply-To: <4BFE90B2.2050604@postnewspapers.com.au>
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On 27/05/2010 11:33 PM, Craig Ringer wrote:
> 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 )

Added as:

http://wiki.postgresql.org/wiki/FAQ#Why_is_my_query_much_slower_when_run_as_a_prepared_query.3F

and the subsequent entry too.

Comments, edits, clarification appreciated. I know it's not as well 
written as it could be, could use archive links, etc; it's just pass 1.


--
Craig Ringer