Anyone here use processes which take up more memory than you have on the box?

Sometimes. If I know that might happen I set the max memory limit for the program at something sane (i.e. less than about 75% of the total amount of RAM). That will kill the process if it tries to get more memory, but since a process that takes up more RAM than you actually have will probably bring the whole system grinding to a halt, it's usually the correct response.

Then I try to fix the code so that it doesn't take as much RAM. update: or add another couple of GB of RAM. I'm currently working on a system that takes about 4 to 8 GB of RAM. Works perfectly fine on a 16 Gb machine.

It doesnt *seem* to be swapping much. The program is still running - but incredibly slowly.

Trust me, the swapping is the cause of the slowness.