The problem isn't "two writes at the same time", it's the server thinking everything's OK for two separate users. If can model your database differently for th

The problem isn't "two writes at the same time", it's the server thinking everything's OK for two separate users. If can model your database differently for this rudimentary example, then good for you – you're thinking about race conditions. Many web programmers do not think about them at all, and race conditions are usually not trivial to fix.