So in the example given here :-GenStage – gen_stage v0.14.0 that of A → B → C I implemented that and saw that the consumer is able to constantly send demands upstream and the numbers are getting printed. But when I created a normal consumer, producer

defmodule Asyncgenstage.Producer do
  use GenStage
  def start_link(_args)  do
    GenStage.start_link(__MODULE__, :ok, name: __MODULE__)
  end

  def init(args) do
    with {:ok, pid} <- :python.start([{:python_path, to_charlist("path")},{:python, 'python3'}]) do
      {:producer, pid}
    end
  end

  def handle_demand(demand, state) do
    result = call_python(state)
    {:noreply, result, state}
  end

  def call_python(pid) do
    call_MFA(pid)
  end

  defp call_MFA(pid) do
    module = :url_generator
    function = :main
    arguments = [10]
    :python.call(pid, module, function, arguments)
  end

end

defmodule Asyncgenstage.Consumer do
  use GenStage
  alias Asyncgenstage.Producer, as: Producer
  def start_link, do: start_link([])
  def start_link(_args) do
    GenStage.start_link(__MODULE__, :ok, name: __MODULE__)
  end

  def init(:ok) do
    {:consumer, :ok, subscribe_to: [{Producer, max_demand: 10, mid_demand: 1}]}
  end


  def handle_events(events, from, state) do
    IO.inspect(events)
    {:noreply, [], state}
  end
end

I observer the demand is not getting send continuously so I thought maybe the the function is not getting called so many times but when I introduced max_demand and min_demand in consumer then it start sending demand upstream constantly. Why is that, max_demand and min_demand are just opts right like by default also we have that value then why on explicitly declaring them is triggering the demand upstream constantly but without them its not.