83 lines
3.0 KiB
Markdown
83 lines
3.0 KiB
Markdown
# telemetry_poller
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[](https://codecov.io/gh/beam-telemetry/telemetry_poller/branch/master/graphs/badge.svg)
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Allows to periodically collect measurements and dispatch them as Telemetry events.
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`telemetry_poller` by default runs a poller to perform VM measurements:
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* `[vm, memory]` - contains the total memory, process memory, and all other keys in `erlang:memory/0`
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* `[vm, total_run_queue_lengths]` - returns the run queue lengths for CPU and IO schedulers. It contains the `total`, `cpu` and `io` measurements
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* `[vm, system_counts]` - returns the current process, atom and port count as per `erlang:system_info/1`
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You can directly consume those events after adding `telemetry_poller` as a dependency.
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Poller also provides a convenient API for running custom pollers.
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## Defining custom measurements
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Poller also includes conveniences for performing process-based measurements as well as custom ones.
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### Erlang
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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:
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```erlang
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telemetry_poller:start_link(
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[{measurements, [
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{process_info, [{name, my_app_worker}, {event, [my_app, worker]}, {keys, [memory, message_queue_len]}]},
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{example_app_measurements, dispatch_session_count, []}
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]},
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{period, timer:seconds(10)}, % configure sampling period - default is timer:seconds(5)
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{name, my_app_poller}
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]).
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```
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Now define the custom measurement and you are good to go:
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```erlang
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-module(example_app_measurements).
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dispatch_session_count() ->
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% emit a telemetry event when called
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telemetry:execute([example_app, session_count], #{count => example_app:session_count()}, #{}).
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```
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### Elixir
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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:
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```elixir
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defmodule ExampleApp.Measurements do
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def dispatch_session_count() do
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# emit a telemetry event when called
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:telemetry.execute([:example_app, :session_count], %{count: ExampleApp.session_count()}, %{})
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end
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end
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```
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```elixir
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:telemetry_poller.start_link(
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# include custom measurement as an MFA tuple
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measurements: [
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{:process_info, name: :my_app_worker, event: [:my_app, :worker], keys: [:message, :message_queue_len]},
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{ExampleApp.Measurements, :dispatch_session_count, []},
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],
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period: :timer.seconds(10), # configure sampling period - default is :timer.seconds(5)
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name: :my_app_poller
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)
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```
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## Documentation
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See [documentation](https://hexdocs.pm/telemetry_poller/) for more concrete examples and usage
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instructions.
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## Copyright and License
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telemetry_poller is copyright (c) 2018 Chris McCord and Erlang Solutions.
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telemetry_poller source code is released under Apache License, Version 2.0.
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See [LICENSE](LICENSE) and [NOTICE](NOTICE) files for more information.
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