Because system RAM is one of the most scarce resources on the PythonAnywhere servers, we limit your processes to a maximum in-memory size of 3GB. This is a per-process limit, not a system-wide one, so if you have larger memory needs, you may be able to do the processing you need by running multiple smaller processes.
If you find you definitely need more RAM than this, one option is a private server inside the PythonAnywhere cluster. However, this is expensive -- the cheapest option right now is $150 per month.
If a process goes over the memory limit, it will be killed. You will normally get an email about this, unless you have previously unsubscribed from our tarpit emails, or from all communications from us.