[STATSGRASS] multi session slow down

[rsadler at cyllene.uwa.edu.au]

Dear List,

I have implemented Monte Carlo inference for a random closed set model  
that mimics the different "phases" of vegetation patterning to be  
found in images of a semi-arid grassland in north west Australia. The  
procedure is implemented using the multiple sessions capability of  
grass60 on a computing cluster with shared disk space. The problem is  
that when running a single machine alone I can generate 500  
simulations an hour. However when I run all 30 machines concurrently  
simulation rate drops dramatically to 20 sessions an hour for a single  
machine (all machines are the same).

I am first contacting the statsgrass list because the procedure uses  
the grass/R interface for a number of separate tasks. What I don't  
know is whether the slow down is a result of the grass/R interface or  
whether the slow done occurs on the grass side of things where there  
is some shared file that all sessions use (like .grass.bashrc but not  
that). The program is run as an R batch file using vanilla and slave,  
with all output is being written to separate text files. All sessions  
use different locations and therefore different mapsets.

Please advise

Regards
Rohan Sadler

PhD Student
School of Plant Biology
School of Mathematics and Statistics
Bushfire Cooperative Research Centre
The University of Western Australia