[postgis-devel] [PostGIS] #1422: [raster] Issues with Mapserver and GDAL

[PostGIS]

#1422: [raster] Issues with Mapserver and GDAL
----------------------------+-----------------------------------------------
 Reporter:  robe            |       Owner:  pracine      
     Type:  defect          |      Status:  new          
 Priority:  medium          |   Milestone:  PostGIS 2.0.0
Component:  postgis raster  |     Version:  trunk        
 Keywords:                  |  
----------------------------+-----------------------------------------------

Comment(by rouault):

 I don't think MapServer is involved at all in that issue. It only relies
 on the GDAL PostgisRaster driver, where actually you can find the culprit
 request :

 {{{
         osCommand.Printf("select o_table_name, overview_factor, o_column,
 "
                 "o_table_schema from raster_overviews where r_table_schema
 = "
                 "'%s' and r_table_name = '%s' and r_column = '%s'",
                 poDS->pszSchema, poDS->pszTable, poDS->pszColumn);
 }}}

 The same for the other request :

 {{{
         osCommand.Printf("select rid, %s from %s.%s where %s ~ "
                 "st_setsrid(st_makebox2d(st_point(%f, %f), st_point(%f,"
                 "%f)),%d)", pszColumn, pszSchema, pszTable, pszColumn,
                 dfProjLowerLeftX, dfProjLowerLeftY, dfProjUpperRightX,
                 dfProjUpperRightY, poPostGISRasterDS->nSrid);
 }}}

 Once the PostgisRaster driver is optimized, MapServer performance should
 improve.

 Looking a bit at the driver, I also see things in the
 PostGISRasterDataset::IRasterIO() implementation, in particular the
 bBlocksCached concept, that lead me to think that only the first call to
 IRasterIO() will be properly optimized (and potentially too much
 agressively optimized if the query window is larger than the GDAL block
 cache size!), but if further calls are made with a different window, they
 will fallback to the non-optimized IReadBlock().

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/1422#comment:3>
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