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Re: Proposed patch to make mergejoin cost estimationmore symmetric

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-patches(at)postgreSQL(dot)org
Subject: Re: Proposed patch to make mergejoin cost estimationmore symmetric
Date: 2007-12-07 14:57:49
Message-ID: 20071207145749.GC5192@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-patches
Tom Lane wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> > I do have a longer term issue that there is no information provided by
> > EXPLAIN to allow us to differentiate these two conditions.
> 
> Sure there is: the new startup condition affects the estimated plan
> startup cost (only) and the existing termination condition affects the
> estimated total cost (only).

Yes, but how can you tell by looking at the explain?  I think the point
is that the "fraction that would be skipped" should be reported somehow.

-- 
Alvaro Herrera                  http://www.amazon.com/gp/registry/5ZYLFMCVHXC
Criptografía: Poderosa técnica algorítmica de codificación que es
empleada en la creación de manuales de computadores.

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Subject: Re: Proposed patch to make mergejoin cost estimationmore symmetric
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