[postgis-tickets] [PostGIS] #4075: Regression between GEOS 3.6.1 and GEOS 3.6.2

[PostGIS]

#4075: Regression between GEOS 3.6.1 and GEOS 3.6.2
----------------------------+--------------------------
 Reporter:  jonaspedersen   |      Owner:  pramsey
     Type:  defect          |     Status:  new
 Priority:  medium          |  Milestone:  PostGIS GEOS
Component:  postgis         |    Version:  2.4.x
 Keywords:  GEOS, ST_Union  |
----------------------------+--------------------------
 After upgrading PostGIS from version 2.4.1 to 2.4.3 (and in the process
 also updating the geos dependency from 3.5.0 to 3.6.2)
 a query on a dataset of 5310482 rows with a geometry of type Polygon which
 used to take around 3.5 hours to complete, now doesn't complete. The query
 is below:
 select
     st_multi((st_dump(geom)).geom)::geometry(multipolygon,25832) as geom
   from (
     select st_union(b.geom) as geom
     from  temp_jonyp.st_union_test  b
     ) foo
 ;

 I've enclosed a sample dataset of 31489 rows.
 Using the sample dataset, the query on the machine with PostGIS 2.4.3
 takes 1 minute and 20 seconds, and on a Windows machine with PosGIS 2.3.2
 (geos 3.5.0) it takes about 20 seconds

 This ticket refers to a discussion on the PostGIS Users Mailing List,
 header 'Performance problems with ST_Union on postgres 9.6, Postgis 2.4.3
 running on top of Red Hat 7.4'
 Version information:
 'PostgreSQL 9.6.8 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5
 20150623 (Red Hat 4.8.5-16), 64-bit POSTGIS="2.4.3 r16312" PGSQL="96"
 GEOS="3.6.2-CAPI-1.10.2 4d2925d6" SFCGAL="1.2.2" PROJ="Rel. 4.9.3, 15
 August 2016" GDAL="GDAL 1.11.4, released 2016/01/25" LIBXML="2.9.1"
 LIBJSON="0.11" RASTER'

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/4075>
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