Hi uhef, yes, messages arriving out of order can be a problem with certain message transports. MessageDB does indeed prevent the case you describe in that once a message is written, unless PG’s sorting functionality fails, it will always return the messages in the order that they were written.
There are, of course, no guarantees as to which message will be written first, but because MessageDB is Just Postgres™ under the hood and uses a query that orders by global_position ASC (message-db/get-category-messages.sql at master · message-db/message-db · GitHub).
Thank you for calling it out, and I agree, that is a good thing to let folks be aware of.