[GRASS5] [bug #2327] (grass) r.cost: too much hard disk access with big regions

[Glynn Clements]

Request Tracker wrote:

> this bug's URL: http://intevation.de/rt/webrt?serial_num=2327
> -------------------------------------------------------------------------
> 
> Subject: r.cost:  too much hard disk access with big regions

> When using r.cost for a 3130 x 4400 cell region, r.cost is very very
> slow. This seems to be because it is spending all its time reading &
> writing to the disk -- the processor use is usually pretty low (sub
> 50%) while it waits. There are four temporary files created in this
> example region, 2x 122mb [in_file, out_file], and two others at the
> end which are both pretty small. Memory use for this example is
> ~126mb. I've got a ~ 70% MASK in place, don't know how much that is
> helping me here. (CELL map)
> 
> It would be great if it could load the temp files into memory instead
> (perhaps by an option flag) to speed up processing for those with lots
> of RAM (here >512mb) on their systems.

r.cost uses the segment library; changing that would probably involve
substantially re-writing r.cost. It would probably also put a ceiling
on the size of maps which it could handle (unless you provide both
segment-based and memory-based implementations of the algorithms).

However: increasing the segments_in_memory variable may help; maybe
this should be controlled by a command-line option.

-- 
Glynn Clements <glynn.clements at virgin.net>