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And in a pathological (but unfortunately not uncommon) pattern, a program (or programs) that need more memory than available can cause "thrashing" where swapping in and out of RAM is happening continuously. This will bring a computer to its knees, making it virtually impossible to do anything on it (slow logins, or logins timing out; any simple command just "hanging" for a long time or never returning). We monitor system usage, and will intervene when we see this happen, by killing termininating the offending process(es) or, in some cases, if possible, or by rebooting the compute server if not.
You can avoid causing a problem like this using the by following tipsthis advice:
Tips:
- Know the memory configuration of the compute server you're using (
- free -g will show you total RAM and swap in Gigabytes
- Before starting a memory intensive job, check the system's current memory status
- free -g also shows used and available for both main memory and swap
- Know the memory requirements of your program.
- Monitor its memory usage while it is running using top (see https://www.booleanworld.com/guide-linux-top-command/)
- This is particularly important if you plan to run multiple instances of a program, since it will guide you in knowing how many such instances you should run.
- Run memory intensive processes when system load is otherwise light (e.g. overnight)
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