[Numpy-discussion] insanely slow writing to memory mapped array

Robert Kern robert.kern at gmail.com
Wed Nov 29 18:51:40 CST 2006

Mathew Yeates wrote:
> Hi
> I have a line in my program that looks like
> outarr[1,:] = computed_array
> where outarr is a memory mapped file. This takes forever.
> I checked and copying  the data using "cp"  at the command line takes 1 
> or 2 seconds. So the problem can't be attributed simply to disk i/o. Is 
> it because the elements are being written one at a time? Any ideas on 
> how to speed this up?

Memory-mapping is highly platform dependent. What platform are you on? What are
the sizes of the arrays? Can you write up a small, self-contained script that
demonstrates the issue so we can experiment and try things out on different

Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco

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