MQTT with Mosquitto

Question

What message queues are supported by Mosqitto ( http://mosquitto.org/ )? Also I want to know in MQTT protocol, a different message queue is created for each topic or it can be done without that in case of memory constraints.

Answer 1

Mosquitto only supports MQTT. MQTT doesn't have the concept of what is normally considered a queue. Having said that, each client has a queue of messages that will be delivered to it. The number of messages in the client queue can be limited with a configuration option. In the future there will be an option to globally limit heap usage and hence the overall length of queues.

Answer 2

Messages may be queued by a broker like Mosquitto in different ways based on the Quality of Service (QoS) specified by the publisher.

See http://2lemetry.com/2013/08/22/mqtt-in-a-nutshell/ for a good description of MQTT QoS.