[postgis-devel] [PostGIS] #1828: Estimate returned by geography_gist_selectivity results in slow query plan for ST_DWithin

[PostGIS]

#1828: Estimate returned by geography_gist_selectivity results in slow query plan
for ST_DWithin
---------------------------+------------------------------------------------
 Reporter:  realityexists  |       Owner:  mcayland     
     Type:  defect         |      Status:  new          
 Priority:  medium         |   Milestone:  PostGIS 2.0.1
Component:  postgis        |     Version:  2.0.x        
 Keywords:                 |  
---------------------------+------------------------------------------------

Comment(by strk):

 And now for geography:
 {{{
 strk=# SELECT count(id) FROM _test_pos WHERE ST_DWithin(pos, 'POINT(7 7)',
 300000);
 NOTICE:  [geography_estimate.c:geography_gist_selectivity:464]
 geography_gist_selectivity called
 NOTICE:  [geography_estimate.c:estimate_selectivity:163]  histogram has 12
 unitsx, 34 unitsy, 36 unitsz
 NOTICE:  [geography_estimate.c:estimate_selectivity:164]  histogram
 geosize is 0.116978x0.321376x0.342003
 NOTICE:  [geography_estimate.c:estimate_selectivity:401]  search_box
 overlaps 1.000000 cells
 NOTICE:  [geography_estimate.c:estimate_selectivity:402]  avg feat
 overlaps 1.000000 cells
 NOTICE:  [geography_estimate.c:estimate_selectivity:414]
 SUM(ov_histo_cells)=0.000000
 NOTICE:  [geography_estimate.c:estimate_selectivity:415]  gain=1.000000
 NOTICE:  [geography_estimate.c:estimate_selectivity:416]
 selectivity=0.000000
 NOTICE:  [geography_estimate.c:geography_gist_selectivity:572]  returning
 computed value: 0.000000
 NOTICE:  [geography_estimate.c:geography_gist_selectivity:464]
 geography_gist_selectivity called
 NOTICE:  [geography_estimate.c:geography_gist_selectivity:507]  no
 variable argument ? - returning default selectivity
  count
 -------
   3839
 (1 row)
 }}}

 The "search_box overlaps 1 cells" is suspicius, isn't it ?

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/1828#comment:19>
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