GenServer that handles network split recovery for Pow.Store.Backend.MnesiaCache.

This should be run on node(s) that has the Pow.Store.Backend.MnesiaCache GenServer running. It'll subscribe to the Mnesia system messages, and listen for :inconsistent_database system events. The first node to set the global lock will find the island with the oldest node and restore that nodes table into all the partitioned nodes.

If a table unrelated to Pow is also affected, an error will be logged and the network will stay partitioned. If you don't mind potential data loss for any of your tables in Mnesia, you can set flush_tables: :all to restore all the affected tables from the oldest node in the cluster.

For better control, you can use unsplit instead of this module.

Usage

To start the GenServer, add it to your application start/2 method:

defmodule MyAppWeb.Application do
  use Application

  def start(_type, _args) do
    children = [
      MyApp.Repo,
      MyAppWeb.Endpoint,
      {Pow.Store.Backend.MnesiaCache, extra_db_nodes: Node.list()},
      Pow.Store.Backend.MnesiaCache.Unsplit
    ]

    opts = [strategy: :one_for_one, name: MyAppWeb.Supervisor]
    Supervisor.start_link(children, opts)
  end

  # ...
end

Strategy for multiple libraries using the Mnesia instance

It's strongly recommended to take into account any libraries that will be using Mnesia for storage before using this module.

A common example would be a job queue, where a potential solution to prevent data loss is to simply keep the job queue table on only one server instead of replicating it among all nodes. When a network partition occurs, it won't be part of the affected tables so this module can self-heal without the job queue table set in :flush_tables.

Initialization options

• :flush_tables - list of tables that may be flushed and restored from the oldest node in the cluster. Defaults to false when only the MnesiaCache table will be flushed. Use :all if you want to flush all affected tables. Be aware that this may cause data loss.