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Re: LIMIT confuses the planner

From: Kouber Saparev <kouber(at)saparev(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: LIMIT confuses the planner
Date: 2009-02-23 18:44:22
Message-ID: 49A2EE86.5070805@saparev.com (view raw or flat)
Thread:
Lists: pgsql-performance
Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> If you left seq_page_cost (which isn't mentioned here) at the default
>> value but reduced random_page_cost to 0.1, then you have
>> random_page_cost < seq_page_cost.  That's probably Bad.
> 
> ... well, it's certainly going to push the planner to believe indexscans
> are cheaper than sorts no matter what.
> 
> The previously noted rowcount estimation problem might be a bigger issue
> in this particular case, but I agree this is a Bad Idea.

So I've set it wrong, I guess. :-)

Now I put it to:

seq_page_cost = 1
random_page_cost = 2

Regards,
-- 
Kouber Saparev
http://kouber.saparev.com

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