Message-ID: <51658BB0.4000808@ca.afilias.info>
Date: Wed, 10 Apr 2013 11:56:32 -0400
From: Steve Singer <ssinger@ca.afilias.info>
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To: "ktm@rice.edu" <ktm@rice.edu>
CC: pgsql-performance@postgresql.org
Subject: Re: slow bitmap heap scans on pg 9.2
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	<20130410135657.GY32580@aart.rice.edu>
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On 13-04-10 09:56 AM, ktm@rice.edu wrote:
> On Wed, Apr 10, 2013 at 09:49:55AM -0400, Steve Singer wrote:

>
> Hi Steve,
>
> The one thing that stands out to me is that you are working with 200GB of
> data on a machine with 4-8GB of ram and you have the random_page_cost set
> to 2.0. That is almost completely uncached and I would expect a value of
> 10 or more to be closer to reality.

Setting random_page_cost to 15 makes the planner choose the nested-loop 
plan (at least the date range I tried).

I thought that the point of effective cache size was to tell the planner 
high likely it is for a random page to be in cache.  With 200GB of data 
for this query and an effective cache size of 3.5 GB I would have 
expected that to be accounted for.


>
> Regards,
> Ken
>
>


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