Add Sentry's Sampler for OTel

Author: solnic

config/config.exs

@@ -17,4 +17,7 @@ end
 
 config :opentelemetry, span_processor: {Sentry.OpenTelemetry.SpanProcessor, []}
 
+config :opentelemetry,
+  sampler: {Sentry.OpenTelemetry.Sampler, [drop: ["Elixir.Oban.Stager process"]]}
+
 config :phoenix, :json_library, Jason

lib/sentry/opentelemetry/sampler.ex

@@ -0,0 +1,27 @@
+defmodule Sentry.OpenTelemetry.Sampler do
+  @moduledoc false
+
+  def setup(config) do
+    config
+  end
+
+  def description(_) do
+    "SentrySampler"
+  end
+
+  def should_sample(
+        _ctx,
+        _trace_id,
+        _links,
+        span_name,
+        _span_kind,
+        _attributes,
+        config
+      ) do
+    if span_name in config[:drop] do
+      {:drop, [], []}
+    else
+      {:record_and_sample, [], []}
+    end
+  end
+end

lib/sentry/opentelemetry/span_processor.ex

@@ -62,10 +62,6 @@ defmodule Sentry.OpenTelemetry.SpanProcessor do
     :ok
   end
 
-  # TODO: "Elixir.Oban.Stager process" is an internal span and it produces a lot of noise
-  #       so it makes sense to ignore it - should this be configurable?
-  defp build_transaction(%{name: "Elixir.Oban.Stager process"}, _), do: nil
-
   defp build_transaction(root_span_record, child_span_records) do
     root_span = build_span(root_span_record)
     child_spans = Enum.map(child_span_records, &build_span(&1))

test/sentry/opentelemetry/sampler_test.exs

@@ -0,0 +1,19 @@
+defmodule Sentry.Opentelemetry.SamplerTest do
+  use Sentry.Case, async: false
+
+  alias Sentry.OpenTelemetry.Sampler
+
+  test "drops spans with the given name" do
+    assert {:drop, [], []} =
+             Sampler.should_sample(nil, nil, nil, "Elixir.Oban.Stager process", nil, nil,
+               drop: ["Elixir.Oban.Stager process"]
+             )
+  end
+
+  test "records and samples spans with the given name" do
+    assert {:record_and_sample, [], []} =
+             Sampler.should_sample(nil, nil, nil, "Elixir.Oban.Worker process", nil, nil,
+               drop: []
+             )
+  end
+end

test_integrations/phoenix_app/config/config.exs

@@ -63,6 +63,9 @@ config :phoenix, :json_library, Jason
 
 config :opentelemetry, span_processor: {Sentry.OpenTelemetry.SpanProcessor, []}
 
+config :opentelemetry,
+  sampler: {Sentry.OpenTelemetry.Sampler, [drop: ["Elixir.Oban.Stager process"]]}
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{config_env()}.exs"