Dumb broker/Smart producer implies that the broker does not attempt to track which messages have been read by each consumer and only retain unread messages; rather, the broker retains all messages for a set amount of time, and consumers are responsible to track what all messages have been read.
Apache Kafka employs this model only wherein the broker does the work of storing messages for a time (7 days by default), while consumers are responsible for keeping track of what all messages they have read using offsets.
The opposite of this is the Smart Broker/Dumb Consumer model wherein the broker is focused on the consistent delivery of messages to consumers. In such a case, consumers are dumb and consume at a roughly similar pace as the broker keeps track of consumer state. This model is followed by RabbitMQ.
