Skip site navigation (1) Skip section navigation (2)

function performs differently with different values

From: Ben Chobot <bench(at)silentmedia(dot)com>
To: PostgreSQL - Performance <pgsql-performance(at)postgresql(dot)org>
Subject: function performs differently with different values
Date: 2010-04-10 20:47:58
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
I've got a sql language function which does a fairly simple select from a table. If I give it one value, it performs quickly (half a ms). If I give it another value, it does not (1.1 seconds). When I run the equivalent select outside of the function, both values perform roughly the same (even though one value returns 140k more rows, as expected). 

My understanding is that this generally happens because the plan should be different for the different values, but the first time the function is run it caches the plan for one of the values and will never use the appropriate plan for the second value. However, when I do an explain analyze of the raw sql for both values, I get the same plan. So my understanding must be wrong?

I suppose the other possibility is that the slower value is slower in a function because it's returning 140k more rows and the function has to deal with that additional data..... but that seems far-fetched, given that each row is just an int.


pgsql-performance by date

Next:From: Ľubomír VargaDate: 2010-04-10 21:42:21
Subject: Re: Some question
Previous:From: Krzysztof KardasDate: 2010-04-10 18:54:04
Subject: Re: PostgreSQL with Zabbix - problem of newbe

Privacy Policy | About PostgreSQL
Copyright © 1996-2017 The PostgreSQL Global Development Group