# 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. Default is `fifo`. ``` 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 eventual consistent nature of the subscriber store it is possible that during queue migration messages still arrive on the old cluster node. This parameter enables to compensate this by keeping the queue around for some 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 ```