Advanced Options

There are a couple of hidden options you can set in the vernemq.conf file. Hidden means that you have to add and set the value explicitly. Hidden options still have default values. Changing them should be considered advanced, possibly with the exception of setting a max_message_rate.

Queue Deliver mode

Specify how the queue should deliver messages when multiple sessions are allowed. In case of fanout all the attached sessions will receive the message, in case of balance an attached session is choosen randomly.

queue_deliver_mode = balance

Queue Type

Specify how queues should process messages, either the fifo or lifo way, with a default setting of fifo. The setting will apply globally, that is, for every spawned queue in a VerneMQ broker. (You can override the queue_type setting in plugins in the auth_on_register hook).

queue_type = fifo

Max Message Rate

Specifies the maximum incoming publish rate per session per second. Depending on the underlying network buffers this rate isn't enforced. Defaults to 0, which means no rate limits apply. Setting to a value of 2 limits any publisher to 2 messages per second, for instance.

max_message_rate = 2

Max Drain Time

Due to the eventually consistent nature of the subscriber store it is possible that during queue migration messages still arrive on the old cluster node. This parameter enables compensation for that fact by keeping the queue around for some configured time (in seconds) after it was migrated to the other cluster node.

max_drain_time = 20

Max Msgs per Drain Step

Specifies the number of messages that are delivered to the remote node per drain step. A large value will provide a faster migration of a queue, but increases the waste of bandwidth in case the migration fails.

max_msgs_per_drain_step = 1000

Default Reg View

Allows to select a new default reg_view. A reg_view is a pre-defined way to route messages. Multiple views can be loaded and used, but one has to be selected as a default. The default routing is vmq_reg_trie, i.e. routing via the built-in trie data structure.

vmq_reg_view = "vmq_reg_trie"

Reg Views

A list of views that are started during startup. It's only used in plugins that want to choose dynamically between routing reg_views.

reg_views = "[vmq_reg_trie]"

Outgoing Clustering Buffer Size

An integer specifying how many bytes are buffered in case the remote node is not available. Default is 10000

outgoing_clustering_buffer_size = 15000

Max Connection Lifetime

Defines the maximum lifetime of MQTT connection in seconds. Max_connection_lifetime can be set per-listener. This is an implementation of MQTT security proposal: "Servers may close the Network Connection of Clients and require them to re-authenticate with new credentials."

listener.max_connection_lifetime = 25000

It is possible to override the value in auth_on_register(_m5) to a lower limit.