[ncl-talk] The slow down when addfile is used in do loop

[Kyle Griffin]

Your problem sounds like it has nothing to do with NCL. It is more likely
that you are running out of memory (RAM) on your computer and your machine
is then having to use swap space (used just like memory, but it's on the
hard drive and hence slower). Things that have been loaded in memory
previously and not yet overwritten will be "fast" to load as no new memory
will need to be written. I would suggest either running the script on a
machine with more RAM or trying to find a way to process the data in
smaller chunks (e.g. a year at a time). Good luck!


Kyle

----------------------------------------
Kyle S. Griffin
Department of Atmospheric and Oceanic Sciences
University of Wisconsin - Madison
Room 1421
1225 W Dayton St, Madison, WI 53706
Email: ksgriffin2 at wisc.edu

On Fri, Sep 12, 2014 at 3:31 PM, Ruping Mo <rupingmo at gmail.com> wrote:

> Hi NCLers,
>
> I have an archive of large grib files. Each grib file contains a month of
> multiple daily global variables. I use the following script to extract a
> small part of one variable. The script, which uses addfile in a large loop,
> runs very fast for the first few months, then begins to slow down
> substantially. I let it run for a few years, then terminate the job
> (Ctrl-Z) and re-run the same script. Surprisingly, the new job runs very
> fast to the month when the previous job was terminated. I wonder why it
> behaves this way, and what I can do to avoid the slow down problem.
>
> Have a nice day!
>
> Ruping
>
> The script:
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> begin
>  nday = 12784     ; number of days from Jan 1979 to Dec 2013
>  temp = new((/nday, 9, 9/), float)
> ;;;;
>  t0 = 0
>  do yr = 1979, 2013
>    syr = tostring(yr)
>    do mo = 1, 12
>     smo = tostring(mo)
>     print(syr + "-" + smo)
>     fname = syr + "/" + syr + "-" + smo + ".grib"
>     dat = addfile(fname, "r")
>     mday = getfilevardimsizes(dat, "initial_time0") - 1
>     i1 = i0 + mday
>     temp(i0:i1, :, :) = (/ dat->2T_GDS0_SFC(:, 80:88, 146:154) /)
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; 2T_GDS0_SFC(mday, 241, 480)
>     i0 = i1 + 1
>    end do
>  end do
> end
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>
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