[postgis-tickets] [PostGIS] #2133: [raster] possible performance issue with ST_MapAlgebra

[PostGIS]

#2133: [raster] possible performance issue with ST_MapAlgebra
---------------------+------------------------------------------------------
  Reporter:  robe    |       Owner:  dustymugs    
      Type:  defect  |      Status:  reopened     
  Priority:  medium  |   Milestone:  PostGIS 2.1.2
 Component:  raster  |     Version:  trunk        
Resolution:          |    Keywords:  history      
---------------------+------------------------------------------------------

Comment(by robe):

 when writing up book playing around with climate data from:
 http://biogeo.ucdavis.edu/data/climate/worldclim/1_4/tiles/cur/tmean_26.zip
 (tiled to 256x256)


 IF I do an operation like:


 {{{

 -- takes 7580 ms
 INSERT INTO tmean_cel(rid, rast)
 SELECT rid,
     ST_MapAlgebra(rast, 1, '32BF'::text,
      '[rast.val]/10.0'::text, -999)
   FROM tmean AS t LIMIT 10;
 }}}

 {{{

 -- takes 6480 ms
 INSERT INTO tmean_cel(rid, rast)
 SELECT rid,
     ST_MapAlgebraExpr(rast, 1, '32BF'::text,
      '[rast.val]/10.0'::text, -999)
   FROM tmean AS t LIMIT 10;
 }}}


 I'll try to prepare a self-contained example to demonstrate the point

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/2133#comment:12>
PostGIS <http://trac.osgeo.org/postgis/>
The PostGIS Trac is used for bug, enhancement & task tracking, a user and developer wiki, and a view into the subversion code repository of PostGIS project.