Hi folks,

I cannot make telemetry (version 1.0.0) work with postgrex (version 0.15.11). Per the db_connection doc (version 2.4.0), a telemetry event is generated when there is a connection error :

A [:db_connection, :connection_error] event is published whenever a connection checkout receives a %DBConnection.ConnectionError{} .

The output of my test is copy/pasted below and as you can see the “Connected to DB” and “Disconnected from DB” messages are displayed because I installed a connection listener with the :connection_listeners option (I am starting/stopping the PostgreSQL instance). I do not get the telemetry event I have attached to. Any idea to make it work ? TIA

$ iex -S mix
Erlang/OTP 24 [erts-12.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]
Interactive Elixir (1.12.3) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> {:ok, pid} = TestPg.start_link([])
{:ok, #PID<0.235.0>}
08:36:05.840 [error] Postgrex.Protocol (#PID<0.239.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (xxx:5433): connection refused - :econnrefused
08:36:17.848 [info]  Connected to DB
08:36:25.207 [error] Postgrex.Protocol (#PID<0.239.0>) disconnected: ** (Postgrex.Error) FATAL 57P01 (admin_shutdown) terminating connection due to administrator command
08:36:25.208 [error] Postgrex.Protocol #PID<0.239.0> could not cancel backend: tcp connect: connection refused - :econnrefused
08:36:25.209 [info]  Disconnected from DB
08:36:25.212 [error] Postgrex.Protocol (#PID<0.239.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (xxx:5433): connection refused - :econnrefused
08:36:35.158 [info]  Connected to DB

defmodule TestPg do

  require Logger

  use GenServer

  @db_host     "xxx"
  @db_port     5433
  @db_name     "test"
  @db_username "test"
  @db_password "dummy"

  defstruct [:pid, :connected]

  def start_link(args) do
    GenServer.start_link(__MODULE__, args, name: :db_test)
  end

  def init(_args) do
    send(self(), :connect)
    :ok = :telemetry.attach("dummy", [:db_connection, :connection_error], &TestPg.handle_event/4, nil)
    {:ok, %__MODULE__{connected: false}}
  end

  # def handle_event(event, measurements, metadata, _config) do
  #   IO.inspect event, label: "event"
  #   IO.inspect measurements, label: "measurements"
  #   IO.inspect metadata, label: "metadata"
  # end

  def handle_event([:db_connection, :connection_error], measurements, metadata, _config) do
    IO.inspect measurements, label: "measurements"
    IO.inspect metadata, label: "metadata"
    # IO.inspect config, label: "config"
  end

  def handle_info(:connect, state) do
    res = Postgrex.start_link(
      hostname: @db_host,
      port:     @db_port,
      database: @db_name,
      username: @db_username,
      password: @db_password,
      connection_listeners: [:db_test]
    )
    case res do
      {:ok, pid} ->
        {:noreply, %__MODULE__{state | pid: pid}}
      {:error, reason} ->
        Logger.error "Postgrex.start_link error for reason #{inspect(reason)}"
        {:stop, reason, state}
    end
  end

  def handle_info({:connected, _pid}, state) do
    Logger.info "Connected to DB"
    {:noreply, %__MODULE__{state | connected: true}}
  end

  def handle_info({:disconnected, _pid}, state) do
    Logger.info "Disconnected from DB"
    {:noreply, %__MODULE__{state | connected: false}}
  end

  def handle_info(msg, state) do
    Logger.warning "Unknown handle_info(): #{inspect(msg)}"
    {:noreply, state}
  end

  def handle_cast(msg, state) do
    Logger.warning "Unknown handle_cast(): #{inspect(msg)}"
    {:noreply, state}
  end

  def handle_call(request, _from, state) do
    Logger.warning "Unknown handle_call(): #{inspect(request)}"
    {:reply, nil, state}
  end

end