[R] Does R accumulate memory

[Duncan Murdoch]

On Sat, 8 Jan 2005 16:38:31 -0500, "Doran, Harold" <HDoran at air.org>
wrote:

>Dear List:
>
>I am running into a memory issue that I haven't noticed before. I am
>running a simulation with all of the code used below. I have increased
>my memory to 712mb and have a total of 1 gb on my machine.
>
>What appears to be happening is I run a simulation where I create 1,000
>datasets with a sample size of 100. I then run each dataset through a
>gls and obtain some estimates.
>
>This works fine. But, when I view how much memory is being used in
>Windows, I see that it does not reduce once the analysis is complete. As
>a result, I must quit R and then perform another analysis. 

If you ask Windows how much memory is being used, you'll likely get an
incorrect answer.  R may not release memory back to the OS, but it may
be available for re-use within R.

Call gc() to see how much memory R thinks is in use.

>So for example, before starting the 1st simulation, my windows task
>manager tells me I am using 200mb of memory. After running the first
>simulation it may go up to 500mb. I then try and run another simulation
>with a larger sample size, but I quickly run out of memory because it
>starts at 500 and increases from there and the simulation halts.

The difficulty you're running into may be memory fragmentation.  When
you run with a larger sample size, R will try to allocate larger
chunks than it did originally.  If the "holes" created when the
original simulation is deleted are too small, R will need to ask
Windows for new memory to store things in.

You could try deleting everything in your workspace before running the
2nd simulation; this should reduce the fragmentation.  Or you could
run the big simulation first, then the smaller one will fit in the
holes left from it.


Duncan Murdoch