[di4na]

A couple of answers : 1) anything that is not just a PoC with limited amount of people connecting to it. For 10 clients connected at all, sure use the thing you know well. It will be easier to use and write, and your time to market will be better. Otherwise, use the real tool.

2) db is rarely your problem. Interpretation can be, and tons of other things. Also erlang schedules things far better and use all the core of the machine, so it will block far less, etc It also means that the thourgput and latency will stay stable despite the amount of users growing. (up to a limit, but it will far higher)

3) Store it in memory. And link other node to yours. Tadaaa

4) Where data live depends of your use case but why use a db if you do not need it anyway?

The thing in general is that web framework tend to use db to hide concurrency.

Also why no cache : because cache is complex, cost you another dependency and another program, make debugging harder, make your app less deterministic, etc. If you need cache use it. But caching is a really hard thing.