Then you have https://en.m.wikipedia.org/wiki/Birthday_problem https://en.m.wikipedia.org/wiki/Birthday_problem Even with a small number of users per second (l

Then you have https://en.m.wikipedia.org/wiki/Birthday_problem https://en.m.wikipedia.org/wiki/Birthday_problem Even with a small number of users per second (like 20) it becomes likely to happen often.