MQTT spec:

the Server MUST send the retained messages matching the Topic Filter of the subscription to the Client

However, RabbitMQ does not send retained messages for Topic Filters containing wildcards.

The solution should comply with at least the following requirements:

1. The solution should be (somewhat) efficient. For example if there are 100k retained messages, if a new client subscribes, the solution must not perform a full table scan over all 100k retained messages/topics.
2. The solution must not overload the broker. For example if there are 100k retained messages, and a client subscribes with a topic filter matching 50k of these retained messages, the broker must not send all 50k messages in one go.