Message-ID: <50FEA640.10201@dunslane.net>
Date: Tue, 22 Jan 2013 09:46:24 -0500
From: Andrew Dunstan <andrew@dunslane.net>
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To: rudi <rudolone@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: High CPU usage after partitioning
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On 01/22/2013 09:21 AM, rudi wrote:
> On Tue, Jan 22, 2013 at 3:04 PM, Merlin Moncure <mmoncure@gmail.com 
> <mailto:mmoncure@gmail.com>> wrote:
>
>     let's see the query -- it's probably written in such a way so as to
>     not be able to be optimized through CE.
>
>
> The query is pretty simple and standard, the behaviour (and the plan) 
> is totally different when it comes to a partitioned table.
>
> Partioned table query => explain analyze SELECT  "sb_logs".* FROM 
> "sb_logs"  WHERE (device_id = 901 AND date_taken = (SELECT 
> MAX(date_taken) FROM sb_logs WHERE device_id = 901));
>

And there you have it. Constraint exclusion does not work in cases like 
this. It only works with static expressions (such as a literal date in 
this case).

cheers

andrew


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