An Mnesia-based cache for messages.

Please note that this module is only compiled if Mnesia is available on your system. See the Mnesia section of the State documentation for more information.

To retrieve the table name used by this cache, use table/0.

By default, the cache will store up to 10_000 messages, and will evict the 100 oldest messages when the limit is reached.

The reason for the eviction count is that with mnesia it is more efficient to find X oldest records and delete them all at once than to find the oldest record and delete it each time a new record is added.

The Mnesia cache supports the following configuration options:

• size_limit: The maximum number of messages to store in the cache. default: 10_000
• eviction_count: The number of messages to evict when the cache is full. default: 100
• table_name: The name of the Mnesia table to use for the cache. default: :nostrum_messages
• compressed: Whether to use compressed in memory storage for the table. default: false
• type: Sets the type of Mnesia table created to cache messages. Can be either :set or :ordered_set, by choosing :ordered_set the eviction of the oldest messages will be more efficient, however it means that the table cannot be changed to only store its contents on disk later. default: :ordered_set

To change this configuration, you can add the following to your config.exs:

config :nostrum,
  caches: %{
    messages: {Nostrum.Cache.MessageCache.Mnesia,
               size_limit: 1000, eviction_count: 50,
               table_name: :my_custom_messages_table_name,
               compressed: true, type: :set}
  }

You can also change the table name used by the cache by setting the table_name field in the configuration for the messages cache.