Hi David:
1) When constructing a postgis you need to be careful to avoid triggering a
call to ST_Extent() which can be very slow. Basically you best bet is to
calculate the extent of your table once and then always pass the extent as an
option when you create the postgis datasource, eg. extent='-179,-60,179,60'
Also, if you pass the srid and the name of the geometry table (in your case
'web_plotgeometry') that will also allow mapnik to skip a few setup queries and
get going rendering even faster.
2) Have you vacuumed recently?
3) It appears you are requiring mapnik to re project geometries on the fly. If
you store you data in the map projection your renders will be faster.
Dane
On Apr 12, 2011, at 4:50 PM, David Wiesen wrote:
> I have been using mapnik for a while with a rather small PostGIS database.
> Recently, my database became significantly larger (currently about 8 million
> geometries),
> and I am now seeing calls to render() being very slow (20-30 seconds).
>
> I believe my database is properly indexed, and I've noticed that mapnik's
> queries run extremely quickly. For example:
>
> SELECT AsBinary("geometry",'NDR') AS geom,"color","nohood" from (select
> geometry, color, 1 as nohood from web_plotgeometry WHERE neighborhood_id=1)
> as web_plotgeometry WHERE "geometry" && SetSRID('BOX3D(-122.1830749511719
> 37.47703779669804,-122.1817016601562 37.4781276287212)'::box3d, 4326);
>
> executes almost instantly.
>
> Furthermore, my features are not very complex, and the tiles I am generating
> don't have a lot of features on them
> (roughly dozens, usually). So I'm wondering if anyone has hints on where the
> slowdown is
>
> At a basic level, here is the relevant part of my code.
>
> Thanks for looking!
> David
>
> ---------------
>
> lyr = Layer('Neighborhood, '+init=epsg:4326')
> lyr.datasource = PostGIS(host='localhost', user='postgres', password='',
> dbname='nextdoor',
> table='(select geometry, color, 1 as snohood from
> web_plotgeometry WHERE neighborhood_id=%s) as web_plotgeometry' % hood.id)
>
> map_obj = Map(int(query['WIDTH']), int(query['HEIGHT']), '+init=epsg:3857')
> map_obj.append_style('color', self.style) # self.style is a very simple style
> with 3 rules.
>
> bbox = map(float, query['BBOX'].split(','))
> map_obj.zoom_to_box(Envelope(*bbox))
>
> image = Image(int(query['WIDTH']), int(query['HEIGHT']))
>
> # SLOW
> render(map_obj, image)
> png_data = image.tostring(common.PIL_TYPE_MAPPING[query['FORMAT']])
> return png_data
>
>
>
>
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