[postgis-users] Performance and memory problems

[strk]

What C++ compiler do you have (name/version) ?

--strk;

andrea.aime wrote:
> Andrea Aime wrote:
> 
> > Hi all,
> > yesterday I've started playing with postgis. Nice tool.
> > For the record, since I wanted to play with sources and did not
> > want to break a working machine, I've set up a Linux mandrake 9.1
> > in a VMWare virtual machine, got the pg 7.4, geos, postgis 0.8 sources 
> > and compiled everything (proj is available as an rpm), set up and loaded 
> > some shapefile into the dbms, created the r-tree indexes (oh, I also 
> > increased the postgres shared memory to around 64MB).
> > 
> > Now, loading speed is acceptable, index creation is fast (less than a 
> > second even with thousands of geometries), but when
> > using geos I start to feel the pain. Example: I have two shapefiles
> > downloaded from http://nationalatlas.gov/atlasftp.html, specifically
> > http://edcftp.cr.usgs.gov/pub/data/nationalatlas/countyp020.tar.gz
> > and http://edcftp.cr.usgs.gov/pub/data/nationalatlas/hucs00m020.tar.gz 
> > (but using only the polygonal file contained in this tar),
> > that is, conties and hydrologic units, that are about 14 MB each
> > (6000 counties and 5000 hydrologic units).
> > 
> > I want to overlay them with the following command:
> > 
> > select intersection(counties.the_geom, hydrounit_poly.the_geom), 
> > counties.county, hydrounit_poly.map_label, hydrounit_poly.reg_name
> > into hydro_counties
> > from counties, hydrounit_poly
> > where counties.the_geom && hydrounit_poly.the_geom
> > 
> > Explain says that the spatial indexes are used. After 30 seconds of 
> > intense computation the backend bombs out due to an out of memory...
> > why? The overlay process should keep in memory only the current 
> > reference geometry from conties and the intersecting ones from 
> > hydrounit_poly, that is, a few kylobytes...
> > Moreover I see that the postmaster actually doing the computation was
> > using 12 MB or resident memory and 6 MB of shared memory (top output),
> > so I don't see why it bombs in the first place...
> > 
> 
> I increased the shared memory but no luck, it bombs anyway. I now 
> suspect is not a memory problem. Backend exits with signal 11.
> I've also checked the geometries with the statements:
> 
> select count(*) from counties where not isValid(the_geom);
> select count(*) from hydrounit_poly where not isValid(the_geom);
> 
> but both returns 0. Any suggestion?
> 
> Best regards
> Andrea Aime
> 
> 
> 
> 
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