mnesia is great, and you can get very far before you would make the jump to anything else. And it can be way faster then any other database. For obvious reasons.
Although it would be great if it spoke SQL, maybe one day it will: https://github.com/elixir-dbvisor/sql since we can already pass it and get the AST.
And when you do have to jump off, you'll be screwed. Because the jump off is usually from in-memory Mnesia with guaranteed sub-millisecond responses to a proper database with at least a magnitude higher latency. And you realize that your app is completely dependent on sub-millisecond responses :)
Low latency is addictive. And by the time when you think you might need to change you’re probably become such a skilled engineer that you realize that everybody that shit on mnesia does not know what they talk about. :)
Although it would be great if it spoke SQL, maybe one day it will: https://github.com/elixir-dbvisor/sql since we can already pass it and get the AST.