Mist isn't intended to be a message queue, its simply a message passer.

Similar to the old question, "if a tree falls in the woods and no one is there to hear it does it make a sound?" Yes; similarly Mist will send a message whether or not anyone is listening, and will keep sending them whether or not the client is prepared to handle them.

So to the first question, there's not a transactional layer to guarantee the client handled the message. Once a message is sent to the client, it is assumed the client has a mechanism for queuing messages if it can't keep up.

As to the second, the caveat is basically saying that if a message is broadcast and nobody cares about the message (ie: there aren't any subscriptions) then mist isn't going to store the message anywhere, it just gets dropped.

Err, I get that! but I am still wondering on where would I use this ? If I dont need transactional layer or buffering, I could use event listener and dispatcher pattern. Anything more than that, a message queue like ZMQ works. Where does this fit in ?

Oh I see. Sorry for the confusion. The initial need was for a rails app to send data model updates to dashboard clients. Later, as our infrastructure became more micro-service-oriented, mist has been used as a place for the dashboard javascript client to subscribe to a centralized event queue. Each micro-service will publish messages to the mist cluster, and the dashboard can respond accordingly.