Re: simple update query too long

On 05/09/2011 04:39 PM, F T wrote:
> Hi list
>
> I use PostgreSQL 8.4.4. (with Postgis 1.4)
>
> I have a simple update query that takes hours to run.
> The table is rather big (2 millions records) but it takes more than 5 hours
> to run !!
>
> The query is just :
> *UPDATE grille SET inter = 0*
>
> The explain command seems ok :
> "Seq Scan on grille50 (cost=0.00..499813.56 rows=2125456 width=494)"
>
> The table as a geometry field geom (simple, it only stores squares)
> The table définition is :
> *CREATE TABLE grille50
> (
> id integer NOT NULL,
> geom geometry,
> inter integer DEFAULT 0,
> oc1 integer,
> oc2 integer,
> occalc integer,
> CONSTRAINT grille_pkey PRIMARY KEY (id),
> CONSTRAINT enforce_dims_geom CHECK (st_ndims(geom) = 2),
> CONSTRAINT enforce_geotype_geom CHECK (geometrytype(geom) =
> 'POLYGON'::text OR geom IS NULL),
> CONSTRAINT enforce_srid_geom CHECK (st_srid(geom) = 2154)
> )
> WITH (
> OIDS=TRUE
> );
> ALTER TABLE grille OWNER TO postgres;
> CREATE INDEX grille_geom ON grille USING gist (geom);
> CREATE INDEX grille_id ON grille USING btree (id);*
>
>
> So any ideas why is it soo long???
>

You've got three indexes, so you have the update on the table *and* the
three indexes. Moreover, one of your indexes is a GiST with some PostGIS
geometry. It takes usuaully quite some (long) time to update such index.

How big is your table and each index?

--
Guillaume
http://www.postgresql.fr
http://dalibo.com