telemetry_poller

Allows to periodically collect measurements and dispatch them as Telemetry events.

telemetry_poller by default runs a poller to perform VM measurements:

[vm, memory] - contains the total memory, process memory, and all other keys in erlang:memory/0
[vm, total_run_queue_lengths] - returns the run queue lengths for CPU and IO schedulers. It contains the total, cpu and io measurements
[vm, system_counts] - returns the current process, atom and port count as per erlang:system_info/1

You can directly consume those events after adding telemetry_poller as a dependency.

Poller also provides a convenient API for running custom pollers.

Defining custom measurements

Poller also includes conveniences for performing process-based measurements as well as custom ones.

Erlang

First define the poller with the custom measurements. The first measurement is the built-in process_info measurement and the second one is given by a custom module-function-args defined by you:

telemetry_poller:start_link(
  [{measurements, [
    {process_info, [{name, my_app_worker}, {event, [my_app, worker]}, {keys, [memory, message_queue_len]}]},
    {example_app_measurements, dispatch_session_count, []}
  ]},
  {period, 10000}, % configure sampling period - default is 5000
  {name, my_app_poller}
]).

Now define the custom measurement and you are good to go:

-module(example_app_measurements).

dispatch_session_count() ->
    % emit a telemetry event when called
    telemetry:execute([example_app, session_count], #{count => example_app:session_count()}, #{}).

Elixir

First define the poller with the custom measurements. The first measurement is the built-in process_info measurement and the second one is given by a custom module-function-args defined by you:

defmodule ExampleApp.Measurements do
  def dispatch_session_count() do
    # emit a telemetry event when called
    :telemetry.execute([:example_app, :session_count], %{count: ExampleApp.session_count()}, %{})
  end
end

:telemetry_poller.start_link(
  # include custom measurement as an MFA tuple
  measurements: [
    {:process_info, name: :my_app_worker, event: [:my_app, :worker], keys: [:message, :message_queue_len]},
    {ExampleApp.Measurements, :dispatch_session_count, []},
  ],
  period: 10_000, # configure sampling period - default is 5_000
  name: :my_app_poller
)

Documentation

See documentation for more concrete examples and usage instructions.

Copyright and License

telemetry_poller source code is released under Apache License, Version 2.0.

See LICENSE and NOTICE files for more information.