PostgreSQL has its own listen/notify mechanism. It might be useful for cases when we have to manage messaging between different application processes, but would prefer to not use extra dependencies such as Redis.

process.rb

CHANNEL       = "slack_bot"
RESET_CHANNEL = "pg_restart"

ActiveRecord::Base.connection_pool.with_connection do |connection|
  conn = connection.instance_variable_get(:@connection)
  begin
    conn.async_exec "LISTEN #{RESET_CHANNEL}"
    conn.async_exec "LISTEN #{CHANNEL}"
    catch(:break_loop) do
      loop do
        conn.wait_for_notify do |channel, pid, payload|
          p [channel, payload]
          throw :break_loop if channel == RESET_CHANNEL
        end
      end
    end
  rescue => error
    p [:error, error]
  ensure
    conn.async_exec "UNLISTEN *"
  end
end

another-process.rb

User.connection.execute %Q(NOTIFY "slack_bot", params)