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: [adapter: Phoenix.PubSub.PG2]

Options

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