[Rd] Memory management problem?

Prof Brian D Ripley ripley@stats.ox.ac.uk
Tue, 12 Jun 2001 19:16:55 +0100 (GMT Daylight Time)

On Tue, 12 Jun 2001 apjaworski@mmm.com wrote:

> I just ran into the following problem.  I am not sure what causes it, but
> here is the scenario:
> (1) I start R with 512Mb of memory.  (I am on an Win2000 PC with 512Mb of
> physical memory)
> (2) I put a couple of small functions in my workspace and I generate two
> real vectors x and y of length 2^19 (542288) each.
> (3) I save this workspace.  The size of the saved file is about 8.4Mb.
> (4) I run lm to fit y vs. x using an 11 parameter model.  I generate a
> couple of plots.  Everything is fine.  (BTW, this runs out of memory with
> standard 256Mb allocation of maximum memory).
> (5) I regenerate y (it is a simulated example) overwriting the old one.
> (6) I run (4) again and I am getting:
>      Error: cannot allocate vector of size 45056kb
>      Reached total allocation of 512Mb
>       This happens even if I run gc() after (5).
> (7) Now comes an interesting part.  If I save the image right now the size
> of it is about 159Mb although I do not have any new objects in my workspace
> (there is a hidden object .Trace, but it is  small).
> (8) If I do
>      rm(list=ls(pos=1), pos=1)
>       however, the size of the workspace comes back to almost zero.
> I am not sure if this happens on Linux since my Linux box only has 192Mb of
> memory.
> Is this the new memory management problem?  Is there any way around it?

No, it's an old one, called fragmentation, I expect.  There may be no
free space of size 45Mb, and remember R no longer moves objects.  Also,
the allocation over 256Mb may well be fragmented.

I think you have the solution already: remove objects you are no longer

Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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