The original messaging middleware on which RabbitMQ (and other AMQP-capable message brokers) are based is IBM's WebSphere MQ fka MQseries. MQ can be used in a t

The original messaging middleware on which RabbitMQ (and other AMQP-capable message brokers) are based is IBM's WebSphere MQ fka MQseries. MQ can be used in a transactional fashion depending on whether messages are stored or can be timed out, and other QoS. Within CICS, MQ can also participate in distributed transactions along with database transactions, and this would be a typical way to use transactional message processing. And X/Open distributed transactions were one of the earliest open system/Unix standards from around 1983, so have been a well understood architecture outside mainframes as well. That it's beneficial to use Postgres messaging (or Oracle AQ or whatever) for its transactional semantics is kind of accidental and a consequence of folks not wanting to bother with dtx. Even though databases are accessed via networks, truly scalable work distribution can't be achieved using SQL, much less with SQLite. Or in other words, if you're using messaging queues in databases, you could use tables and row locks directly just as well.