Any process can crash in a system. Thats not really the point. The point is that a simple KV store in a GenServer would be the opposite of “clumsy”. It would be so simple that the likelihood of crashing is very low.

I agree with your points about ETS allowing for more performance long term. But there’s overhead in having ETS tables lying around so if you don’t need it then its waste. The idea that always using ets is just better than using a genserver isn’t a solid general rule.

In practice we tend to use a combination of the two. A GenServer will start an ets table and process all writes to that ets table. That way writes are applied serially. However all reading is done in the client process. As an aside, this is why the “boilerplate” of a GenServer is useful. All of this logic is hidden behind that “boilerplate” and is transparent to the end user of the api.

Neither situation is that difficult to test if you want to test in isolation. The api can take an optional name argument and look up the process and ets tables with that name. In production you would use the default name. Thats pattern tends to be less egregious than using something like a mock.

You’re not wrong, but adding ets to the mix is also one more moving piece in your system and it’s more complex than e.g. a simple Agent, which basically does nothing but read state. Not to mention the write side if you need that as well.

So, assuming that my state has a low number of accesses per second, and that using an ETS would provide me with the same failsafe resilience as using a process, I would still be better off using an ETS because it would allow me to easily get concurrent access in the future without ever worrying with bottlenecks.

My point is, if you are going to separate state from work, do it with an ETS table as it grants you more benefits on the long term (meaning you already have concurrent access to state when needed).

As an extra – and more recent – example, @gyson created Ane which combines :ets and Erlang’s recent :atomics module. Haven’t had a chance to use it yet but it looks like a solid compromise between different tradeoffs with a lot of speed and code readability to be gained.

Other options I’d consider:

• Erlang’s recent :persistent_term module.
• FastGlobal.

As others have said, the chance of such simple processes crashing is pretty low – unless you cache things that rely on volatile external APIs or resources (and even then defensive coding can and will save you).

As for caching libraries and primitives, nowadays we have more choice. Evaluate your tradeoffs and take a pick.