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Re: Query timing increased from 3s to 55s when used as function instead of select

From: Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>
To: Tyler Hildebrandt <tyler(at)campbell-lange(dot)net>
Cc: pgsql-performance(at)postgresql(dot)org, Sebastian Ritter <sebastian(at)campbell-lange(dot)net>, rory <rory(at)campbell-lange(dot)net>
Subject: Re: Query timing increased from 3s to 55s when used as function instead of select
Date: 2010-05-27 15:33:06
Message-ID: 4BFE90B2.2050604@postnewspapers.com.au (view raw or flat)
Thread:
Lists: pgsql-performance
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


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