Date: Thu, 7 Jul 2005 10:13:27 +0200
To: pgsql-performance@postgresql.org
Subject: Re: CURSOR slowes down a WHERE clause 100 times?
Message-ID: <20050707081327.GA17054@rigacci.org>
References: <20050706211946.GA3460@rigacci.org>
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From: Niccolo Rigacci <niccolo@rigacci.org>

On Wed, Jul 06, 2005 at 11:19:46PM +0200, Niccolo Rigacci wrote:
> 
> I have a performace problem with the following query:
> 
>   BEGIN;
>   DECLARE mycursor BINARY CURSOR FOR
>     SELECT
>       toponimo,
>       wpt
>       FROM wpt_comuni_view
>         WHERE (
>           wpt &&
>           setSRID('BOX3D(4.83 36, 20.16 47.5)'::BOX3D, 4326)
>         );
>   FETCH ALL IN mycursor;
>   END;
> 
> I get the results in about 108 seconds (8060 rows).
> 
> If I issue the SELECT alone (without the CURSOR) I get the 
> same results in less than 1 second.

By trial and error I discovered that adding an "ORDER BY 
toponimo" clause to the SELECT, boosts the CURSOR performances 
so that they are now equiparable to the SELECT alone.

Is there some documentation on how an ORDER can affect the 
CURSOR in a different way than the SELECT?

-- 
Niccolo Rigacci
Firenze - Italy

War against Iraq? Not in my name!