We use a flavor of event sourcing in production (Elixir+Postgres) and I have found many "rules" can be broken while still maintaining the core benefits of CQRS/

We use a flavor of event sourcing in production (Elixir+Postgres) and I have found many "rules" can be broken while still maintaining the core benefits of CQRS/ES - We use Postgres as the event store and all of our other projections are stored in the same database. - Our app is not distributed. We use a single database. - Our event store is not immutable. Instead we will run migrations to rewrite the events, delete events, etc. You either have to either deal with the complexity of maintaining two versions of code or the complexity of migrating. I've found the later is a fixed cost (do it once and move on) vs. a variable cost (continue to deal with two versions of code). - Our commands aren't async. They are executed inline. - We don't do any snapshotting. Granted, we don't have a lot of users on our app (~50 active users) but overall this has been a positive experience.