[STATSGRASS] multi session slow down

[Joel Pitt]

Without knowing much about the R interface I would guess that it may be slow 
due to all machines trying to access data off of the same disk. Have you got 
any way to measure disk reads and the network bandwidth to the machine 
hosting the disk?

-Joel

On Friday 17 March 2006 2:39 pm, rsadler at cyllene.uwa.edu.au wrote:
> 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
>
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> statsgrass at grass.itc.it
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Joel Pitt, Room B534
Bio-Protection & Ecology Division
PO Box 84, Lincoln University 8150

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