Message-ID: <53AC491A.8090207@optionshouse.com>
Date: Thu, 26 Jun 2014 11:23:54 -0500
From: Shaun Thomas <sthomas@optionshouse.com>
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To: Claudio Freire <klaussfreire@gmail.com>, AJ Weber <aweber@comcast.net>
CC: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: how to improve perf of 131MM row table?
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On 06/26/2014 11:19 AM, Claudio Freire wrote:

> Try changing node_id in (...) into node.id in (...)

Wow. How did we not see that earlier? That's probably the issue. If you 
look at the estimates of his query:

Bitmap Heap Scan on alf_node_properties prop  (cost=1253.19..189491.87 
rows=52790 width=179) (actual time=0.571..1.349 rows=1071 loops=1)

The planner is off by an order of magnitude, and since the matches are 
against node_id instead of node.id, it thinks it would have to index 
seek on the alf_node table for over 50k rows. I could easily see it 
opting for a sequence scan in that case, depending on how high 
random_page_cost is.

-- 
Shaun Thomas
OptionsHouse, LLC | 141 W. Jackson Blvd. | Suite 800 | Chicago IL, 60604
312-676-8870
sthomas@optionshouse.com

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