Phoenix PubSub adapter based on PG2.

To use it as your PubSub adapter, simply add it to your Endpoint's config:

config :my_app, MyApp.Endpoint,
  pubsub: [name: MyApp.PubSub,
           adapter: Phoenix.PubSub.PG2]

To use this adapter outside of Phoenix, you must start an instance of this module as part of your supervision tree:

children = [
  {Phoenix.PubSub.PG2, name: MyApp.PubSub},
  ...
]

Options

• :name - The required registered name and optional node name for pubsub processes, for example: MyApp.PubSub, {MyApp.PubSub, :node@host}. When only a server name is provided, the node name defaults to node().

• :pool_size - Both the size of the local pubsub pool and subscriber shard size. Defaults to the number of schedulers (cores). A single pool is often enough for most use-cases, but for high subscriber counts on single topics or greater than 1M clients, a pool size equal to the number of schedulers (cores) is a well rounded size.