Happy Saturday, Elixir Forum - I’m exploring the Commanded event sourcing library for a potential weekend project. A coworker of mine mentioned that a common concurrency issue in event sourcing is having command handlers write multiple events to a stream when only one written event is valid.
For example, two “close bank account” commands are fired off at the same time, and the handler processes both. Thus, the handler writes two “closed bank accounts” events to the event stream. Only one “closed bank accounts” event should have been written.
Our discussion made me realize that I might not know what I’m getting into when using Event Sourcing - are there other potential concurrency problems that should I be wary of? I see that Commanded has a section related to “Command dispatch consistency guarantee” - does strong consistency protect against common concurrency problems?