[postgis-devel] Try before you Buy

[Bob and Deb]

Btw, I got 15849 ms when I ran this query:

SELECT state,
  SUM(ST_NPoints(the_geom)) As  numpointsbefore,
    ST_NPoints(ST_Union_Fast(the_geom)) As numpointsafter
  FROM usstatebounds
  GROUP BY state
  ORDER BY state;

I was so excited to see unioncascade that I did not adjust my test server
parameters.  Fyi, my server is on a 1.83 Ghz duo core laptop with 2 gigs of
mem running Ubuntu Hardy Heron.

This machine also has the latest postgresql, postgis, and geos installed.

GeoDB=# SELECT PostGIS_Full_Version();
                                  postgis_full_version
----------------------------------------------------------------------------------------
 POSTGIS="1.4.0SVN" GEOS="3.1.0-CAPI-1.5.0" PROJ="Rel. 4.6.1, 21 August
2008" USE_STATS
(1 row)


How do I use _unite_garray_fast(st_geometryarray(the_geom)) with the
usstatebounds?


On Wed, Jan 21, 2009 at 9:01 PM, Paul Ramsey <pramsey at opengeo.org> wrote:

> All the pieces of the new super-fast cascaded geometry are now in SVN.
> You'll need an absolutely fresh copy of GEOS to use them, but once you
> do, you can run something like this:
>
> aggtest=# select
> geometrytype(_unite_garray_fast(st_geometryarray(the_geom))) from
> sample_poly;
>       geometrytype --------------
>  MULTIPOLYGON
> (1 row)
> Time: 23267.905 ms
>
>
> note that
>  st_union() is still bound against the oldest implementation
>  st_union_fast() is bound against an implementation with slow
> aggregation but fast GEOS union
>  _unite_garray_fast(st_geometryarray()) is the only way to get the
> ultimate speed right now
>
> Unfortunately, it looks I'm going to need a special finalfunc for
> every single aggregate that takes in the internal pointer to the
> side-cache. That makes all the aggregates less pretty, since they
> won't use function(geometry[]) as their finalfunc anymore. The
> cleanest way would be to have those finalfuncs do little more than
> call other functions.
>
> Mark, is there a prescribed way to call postgresql functions (ones
> with (PG_FUNCTION_ARGS) as the argument) from other internal
> functions?
>
> Paul
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>
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