Sometimes consumers get overwhelmed by the number of messages they receive. VerneMQ can loadbalance between multiple consumer instances subscribed to the same topic with the same ClientId.
To enable session balancing, activate the following two settings in vernemq.conf
allow_multiple_sessions = on queue_deliver_mode = balance
Note: Currently those settings will activate consumer session balancing globally on the respective node. Restricting balancing to specific consumers only, will require a plugin. Note that you cannot balance consumers spread over different cluster nodes.