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Re: [Maposmatic-dev] Re: PostGIS help for MapOSMatic
From: |
Thomas Petazzoni |
Subject: |
Re: [Maposmatic-dev] Re: PostGIS help for MapOSMatic |
Date: |
Mon, 1 Mar 2010 19:37:40 +0100 |
Hello,
On Mon, 1 Mar 2010 10:12:29 +0100
Jean-Christophe Arnu <address@hidden> wrote:
> That's true, views are evaluated each time.
Ah, that's interesting. This would mean that :
left join cities_area_by_name on city='Toulouse'
has the effect of doing the query in the cities_area_by_name view for
each street, while it is useless.
> Depending on the query it could be painful to get performance out of
> the query. Maybe instead of the view, there might be interesting to
> write an SQL stored procedure with immutable attribute and returning
> a set of (rows) data retrieved by the view. Thus PostgreSQL will
> evalutate the function once and then use the cache for each row, each
> time it is called.
Hum, I'll need to have a look at PostgreSQL stored procedures, because
these things are new for me (I'm a database newbie).
Using the result of explain sent by David Mentré, do you have a more
detailed analysis of the problem ?
Thanks a lot for your feedback!
Thomas
--
Thomas Petazzoni http://thomas.enix.org
Promouvoir et défendre le Logiciel Libre http://www.april.org
Logiciels Libres à Toulouse http://www.toulibre.org
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