I am trying to use the Phoenix.Presence behaviour in my LiveView. I intend to use it to track a channel topic on the LiveSocket, rather than initiating a new socket connection (i.e. UserSocket). There are several online resources covering this topic (e.g. Phoenix Presence with Phoenix LiveView · FullstackPhoenix), but I keep running into an error.

The error in a nutshell: 1st argument: the table identifier does not refer to an existing ETS table. I believe this ‘1st argument’ refers to self() in:

      Presence.track(
        self(),
       "story",
        socket.assigns.current_user.id,
        %{}
      )

I have been looking around for solutions and trying to debug the code, but the error remains. I would like to understand what the issue is.

Below all the relevant source code and error messaging.

defmodule TodayCostoryWeb.Presence do
  use Phoenix.Presence, otp_app: :today_costory,
                        pubsub_server: TodayCostory.PubSub
end

defmodule TodayCostory.Application do
  use Application

  @impl true
  def start(_type, _args) do
    children = [
      ...
      {Phoenix.PubSub, name: TodayCostory.PubSub},
      TodayCostoryWeb.Presence,
      TodayCostoryWeb.Endpoint
    ]

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

defmodule TodayCostoryWeb.StoryLive do
  use TodayCostoryWeb, :live_view
  alias TodayCostoryWeb.Presence
  ...

  def mount(_params, session, socket) do
    socket =
      assign_new(
        socket,
        :current_user,
        fn ->
          Accounts.get_user_by_session_token(session["user_token"])
        end
      )

    if connected?(socket) do
      Presence.track(
        self(),
       "story",
        socket.assigns.current_user.id,
        %{}
      )
      TodayCostoryWeb.Endpoint.subscribe("story")
    end

    ...

    {:ok, socket}
  end

[error] GenServer #PID<0.20718.0> terminating
** (ArgumentError) errors were found at the given arguments:

  * 1st argument: the table identifier does not refer to an existing ETS table

    (stdlib 3.17.1) :ets.lookup(TodayCostoryWeb.Presence, :pool_size)
    (phoenix_pubsub 2.1.1) lib/phoenix/tracker.ex:314: Phoenix.Tracker.pool_size/1
    (phoenix_pubsub 2.1.1) lib/phoenix/tracker.ex:134: Phoenix.Tracker.track/5
    (today_costory 0.1.0) lib/today_costory_web/live/story_live.ex:27: TodayCostoryWeb.StoryLive.mount/3
    (phoenix_live_view 0.17.11) lib/phoenix_live_view/utils.ex:301: anonymous fn/6 in Phoenix.LiveView.Utils.maybe_call_live_view_mount!/5
    (telemetry 1.1.0) /Users/macbookpro2021/Documents/dev/today_costory/deps/telemetry/src/telemetry.erl:320: :telemetry.span/3
    (phoenix_live_view 0.17.11) lib/phoenix_live_view/channel.ex:1001: Phoenix.LiveView.Channel.verified_mount/8
    (phoenix_live_view 0.17.11) lib/phoenix_live_view/channel.ex:59: Phoenix.LiveView.Channel.handle_info/2
    (stdlib 3.17.1) gen_server.erl:695: :gen_server.try_dispatch/4
    (stdlib 3.17.1) gen_server.erl:771: :gen_server.handle_msg/6
    (stdlib 3.17.1) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: {Phoenix.Channel, %{"params" => %{"_csrf_token" => "IhU7Am8bOgAoPxABEhstPCURMnkEGgN5AAtP9UMemjDxpQbrGzPI5J25", "_mounts" => 0, "_track_static" => ["http://localhost:4000/assets/app.css", "http://localhost:4000/assets/app.js"]}, "session" => "SFMyNTY.g2gDaAJhBXQAAAAIZAACaWRtAAAAFHBoeC1GeElZMkZVZE9GVng4M1RuZAAMbGl2ZV9zZXNzaW9uaAJkAAdkZWZhdWx0bggAhhhAP7ANEhdkAApwYXJlbnRfcGlkZAADbmlsZAAIcm9vdF9waWRkAANuaWxkAAlyb290X3ZpZXdkACBFbGl4aXIuVG9kYXlDb3N0b3J5V2ViLlN0b3J5TGl2ZWQABnJvdXRlcmQAHUVsaXhpci5Ub2RheUNvc3RvcnlXZWIuUm91dGVyZAAHc2Vzc2lvbnQAAAAAZAAEdmlld2QAIEVsaXhpci5Ub2RheUNvc3RvcnlXZWIuU3RvcnlMaXZlbgYAVK7dD4MBYgABUYA.cGrahkmk2vmiMJkMvsmJaMN21ic8YHPR_DiblXj6QrU", "static" => "SFMyNTY.g2gDaAJhBXQAAAADZAAKYXNzaWduX25ld2wAAAABZAAMY3VycmVudF91c2VyamQABWZsYXNodAAAAABkAAJpZG0AAAAUcGh4LUZ4SVkyRlVkT0ZWeDgzVG5uBgBUrt0PgwFiAAFRgA.xlF3G3iTjebpn47eOjRIqvj9YPL2nRKS1sX1qlvl1aY", "url" => "http://localhost:4000/"}, {#PID<0.20712.0>, #Reference<0.2939426857.1123287043.49659>}, %Phoenix.Socket{assigns: %{}, channel: Phoenix.LiveView.Channel, channel_pid: nil, endpoint: TodayCostoryWeb.Endpoint, handler: Phoenix.LiveView.Socket, id: "users_sessions:i0LCd7tjBpn7KYtPTQtTT_eJmxSlFOVAB6pG_SIV0vU=", join_ref: "4", joined: false, private: %{connect_info: %{session: %{"_csrf_token" => "cTORVNweEUTybJONbkb01P1L", "live_socket_id" => "users_sessions:i0LCd7tjBpn7KYtPTQtTT_eJmxSlFOVAB6pG_SIV0vU=", "user_token" => <<139, 66, 194, 119, 187, 99, 6, 153, 251, 41, 139, 79, 77, 11, 83, 79, 247, 137, 155, 20, 165, 20, 229, 64, 7, 170, 70, 253, 34, 21, 210, 245>>}}}, pubsub_server: TodayCostory.PubSub, ref: nil, serializer: Phoenix.Socket.V2.JSONSerializer, topic: "lv:phx-FxIY2FUdOFVx83Tn", transport: :websocket, transport_pid: #PID<0.20712.0>}}
State: #Reference<0.2939426857.1123287043.49661>
[error] an exception was raised:
    ** (ArgumentError) errors were found at the given arguments:

  * 1st argument: the table identifier does not refer to an existing ETS table

        (stdlib 3.17.1) :ets.lookup(TodayCostoryWeb.Presence, :pool_size)
        (phoenix_pubsub 2.1.1) lib/phoenix/tracker.ex:314: Phoenix.Tracker.pool_size/1
        (phoenix_pubsub 2.1.1) lib/phoenix/tracker.ex:134: Phoenix.Tracker.track/5
        (today_costory 0.1.0) lib/today_costory_web/live/story_live.ex:27: TodayCostoryWeb.StoryLive.mount/3
        (phoenix_live_view 0.17.11) lib/phoenix_live_view/utils.ex:301: anonymous fn/6 in Phoenix.LiveView.Utils.maybe_call_live_view_mount!/5
        (telemetry 1.1.0) /Users/macbookpro2021/Documents/dev/today_costory/deps/telemetry/src/telemetry.erl:320: :telemetry.span/3
        (phoenix_live_view 0.17.11) lib/phoenix_live_view/channel.ex:1001: Phoenix.LiveView.Channel.verified_mount/8
        (phoenix_live_view 0.17.11) lib/phoenix_live_view/channel.ex:59: Phoenix.LiveView.Channel.handle_info/2
        (stdlib 3.17.1) gen_server.erl:695: :gen_server.try_dispatch/4
        (stdlib 3.17.1) gen_server.erl:771: :gen_server.handle_msg/6
        (stdlib 3.17.1) proc_lib.erl:226: :proc_lib.init_p_do_apply/3