[postgis-tickets] [PostGIS] #3080: PostgreSQL 9.5 regress failure on st_reclass: possible performance regression for all of PostGIS base

[PostGIS]

#3080: PostgreSQL 9.5 regress failure on st_reclass: possible performance
regression for all of PostGIS base
--------------------+-------------------------------------------------------
 Reporter:  robe    |       Owner:  dustymugs    
     Type:  defect  |      Status:  new          
 Priority:  low     |   Milestone:  PostGIS 2.2.0
Component:  raster  |     Version:  trunk        
 Keywords:          |  
--------------------+-------------------------------------------------------
Changes (by robe):

  * owner:  pramsey => dustymugs
  * priority:  blocker => low
  * component:  postgis => raster


Comment:

 Seems I over-reacted.  It appears the change Tom made only changes
 behavior of inline tables and this redundant call stuff has always been
 the case for real tables.

 For example doing this:

 {{{


 DROP TABLE IF EXISTS t2;
 CREATE TABLE t2(rast raster);
 INSERT INTO t2(rast)
 SELECT ST_SetValue(
                         ST_SetValue(
                                 ST_AddBand(
                                         ST_MakeEmptyRaster(100, 100, 10,
 10, 2, 2, 0, 0, 0),
                                         1, '32BF', 1, 0
                                 ),
                                 1, 1, 1, 3.14159
                         ),
                         1, 10, 10, 2.71828
                 ) As rast;

 SELECT
         ST_Value(t.rast, 1, 1, 1),
         ST_Value(t.rast, 1, 10, 10),
         ST_BandNoDataValue(rast, 1)
 FROM (
         SELECT ST_Reclass(
                 rast,
                 ROW(1,
 'a-100]:50-1,(-100-1000]:150-50,(1000-10000]:254-150', '8BUI', 0)
         ) AS rast  FROM t2
 ) AS t;
 }}}

 Forces a call of of ST_Reclass twice even in PostgreSQL 9.4.  So only
 performance degradation would be a constant wrapped in a subquery not
 using a CTE


 So we just need to change this test to have an OFFSET 0 and call it a day.

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/3080#comment:7>
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