[GRASS-dev] Memory consumption using pygrass.utils.get_raster_for_points

[Steven Pawley]

Hello devs,

When running pygrass.utils.get_raster_for_points repeatedly, it appears 
that the python memory allocation continuously increases until all ram 
is consumed, even if the extracted values are not being collected (or 
are overwriting the same variable).

I noticed this when extracting raster data at point locations, when 
using a large point dataset, even though I had pre-allocated a numpy 
array to receive the results.

Below is an example on the nc_spm_08_grass7 example data (in the landsat 
mapset), repeating the operation say 50 times on the same point vector 
dataset. I wouldn't have expected the memory consumption to continuously 
increase for this operation, because I'm overwriting the 'arr' variable 
each time. However, if you repeat this enough times, you will run out of 
system memory and the allocated memory does not appear to be released, 
i.e. even if you manually force garbage collection.

Any suggestions?


from grass.pygrass.vector import VectorTopo
from grass.pygrass.raster import RasterRow
from grass.pygrass.modules.shortcuts import raster as r
from grass.pygrass.gis.region import Region
from grass.pygrass.utils import get_raster_for_points

reg = Region()
reg.from_rast("landclass96")
reg.write()
reg.set_raster_region()

r.random(input="landclass96", npoints=200000, vector="landclass96_roi",
          overwrite=True)

points = VectorTopo("landclass96_roi")
points.open("r")

# repeat spatial query of raster
for i in range(50):
     with RasterRow("lsat5_1987_10") as src:
         arr = get_raster_for_points(points, src)