Date: Wed, 21 May 2008 18:18:27 +0200
To: "Richard Huxton" <dev@archonet.com>,
	"Luke Lonergan" <LLonergan@greenplum.com>
Subject: Re: Posible planner improvement?
From: PFC <lists@peufeu.com>
Cc: albert@sedifa.com, pgsql-performance@postgresql.org
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On Wed, 21 May 2008 15:09:49 +0200, Richard Huxton <dev@archonet.com>  
wrote:

> Luke Lonergan wrote:
>> The problem is that the implied join predicate is not being
>> propagated.  This is definitely a planner deficiency.
>
> IIRC only equality conditions are propagated and gt, lt, between aren't.  
>   I seem to remember that the argument given was that the cost of  
> checking for the ability to propagate was too high for the frequency  
> when it ocurred.
>
> Of course, what was true for code and machines of 5 years ago might not  
> be so today.
>

	Suggestion : when executing a one-off sql statement, optimizer should try  
to offer "best effort while being fast" ; when making a plan that will be  
reused many times (ie PREPARE, functions...) planning time could be  
muuuuch longer...