set "supportability.atm_sampling_ratio" and "sampling.threshold" span… (

#15)

set "supportability.atm_sampling_ratio" and "sampling.threshold" span attributes
Signed-off-by: Joao Grassi <[email protected]>

source/extensions/tracers/opentelemetry/samplers/dynatrace/dynatrace_sampler.cc

@@ -21,7 +21,6 @@ namespace OpenTelemetry {
 namespace {
 
 constexpr std::chrono::minutes SAMPLING_UPDATE_TIMER_DURATION{1};
-const char* SAMPLING_EXTRAPOLATION_SPAN_ATTRIBUTE_NAME = "sampling_extrapolation_set_in_sampler";
 
 class DynatraceTag {
 public:
@@ -73,6 +72,26 @@ class DynatraceTag {
   uint32_t path_info_;
 };
 
+// add Dynatrace specific span attributes
+void addSamplingAttributes(uint32_t sampling_exponent,
+                           std::map<std::string, std::string>& attributes) {
+
+  const auto multiplicity = SamplingState::toMultiplicity(sampling_exponent);
+  // The denominator of the sampling ratio. If, for example, the Dynatrace OneAgent samples with a
+  // probability of 1/16, the value of supportability.atm_sampling_ratio would be 16.
+  // Note: Ratio is also known as multiplicity.
+  attributes["supportability.atm_sampling_ratio"] = std::to_string(multiplicity);
+
+  if (multiplicity > 1) {
+    static constexpr uint64_t two_pow_56 = 1lu << 56; // 2^56
+    // The sampling probability can be interpreted as the number of spans
+    // that are discarded out of 2^56. The attribute is only available if the sampling.threshold is
+    // not 0 and therefore sampling happened.
+    const uint64_t sampling_threshold = two_pow_56 - two_pow_56 / multiplicity;
+    attributes["sampling.threshold"] = std::to_string(sampling_threshold);
+  }
+}
+
 } // namespace
 
 DynatraceSampler::DynatraceSampler(
@@ -118,9 +137,7 @@ SamplingResult DynatraceSampler::shouldSample(const absl::optional<SpanContext>
     if (DynatraceTag dynatrace_tag = DynatraceTag::create(trace_state_value);
         dynatrace_tag.isValid()) {
       result.decision = dynatrace_tag.isIgnored() ? Decision::Drop : Decision::RecordAndSample;
-      // TODO: change attribute name and value in scope of OA-26680
-      att[SAMPLING_EXTRAPOLATION_SPAN_ATTRIBUTE_NAME] =
-          std::to_string(dynatrace_tag.getSamplingExponent());
+      addSamplingAttributes(dynatrace_tag.getSamplingExponent(), att);
       result.tracestate = parent_context->tracestate();
     }
   } else {
@@ -130,8 +147,8 @@ SamplingResult DynatraceSampler::shouldSample(const absl::optional<SpanContext>
     const auto sampling_state = sampling_controller_.getSamplingState(sampling_key);
     const bool sample = sampling_state.shouldSample(hash);
     const auto sampling_exponent = sampling_state.getExponent();
-    // TODO: change attribute name and value in scope of OA-26680
-    att[SAMPLING_EXTRAPOLATION_SPAN_ATTRIBUTE_NAME] = std::to_string(sampling_exponent);
+
+    addSamplingAttributes(sampling_exponent, att);
 
     result.decision = sample ? Decision::RecordAndSample : Decision::Drop;
     // create new forward tag and add it to tracestate

test/extensions/tracers/opentelemetry/samplers/dynatrace/dynatrace_sampler_test.cc

@@ -80,6 +80,8 @@ TEST_F(DynatraceSamplerTest, TestWithoutParentContext) {
                              ::opentelemetry::proto::trace::v1::Span::SPAN_KIND_SERVER, {}, {});
   EXPECT_EQ(sampling_result.decision, Decision::RecordAndSample);
   EXPECT_EQ(sampling_result.attributes->size(), 1);
+  EXPECT_STREQ(
+      sampling_result.attributes->find("supportability.atm_sampling_ratio")->second.c_str(), "1");
   EXPECT_STREQ(sampling_result.tracestate.c_str(), "5b3f9fed-980df25c@dt=fw4;0;0;0;0;0;0;95");
   EXPECT_TRUE(sampling_result.isRecording());
   EXPECT_TRUE(sampling_result.isSampled());
@@ -94,6 +96,8 @@ TEST_F(DynatraceSamplerTest, TestWithUnknownParentContext) {
                              ::opentelemetry::proto::trace::v1::Span::SPAN_KIND_SERVER, {}, {});
   EXPECT_EQ(sampling_result.decision, Decision::RecordAndSample);
   EXPECT_EQ(sampling_result.attributes->size(), 1);
+  EXPECT_STREQ(
+      sampling_result.attributes->find("supportability.atm_sampling_ratio")->second.c_str(), "1");
   // Dynatrace tracesate should be prepended
   EXPECT_STREQ(sampling_result.tracestate.c_str(),
                "5b3f9fed-980df25c@dt=fw4;0;0;0;0;0;0;95,some_vendor=some_value");
@@ -110,6 +114,8 @@ TEST_F(DynatraceSamplerTest, TestWithDynatraceParentContextSampled) {
                              ::opentelemetry::proto::trace::v1::Span::SPAN_KIND_SERVER, {}, {});
   EXPECT_EQ(sampling_result.decision, Decision::RecordAndSample);
   EXPECT_EQ(sampling_result.attributes->size(), 1);
+  EXPECT_STREQ(
+      sampling_result.attributes->find("supportability.atm_sampling_ratio")->second.c_str(), "1");
   // tracestate should be forwarded
   EXPECT_STREQ(sampling_result.tracestate.c_str(), dt_tracestate_sampled);
   // sampling decision from parent should be respected
@@ -126,6 +132,11 @@ TEST_F(DynatraceSamplerTest, TestWithDynatraceParentContextIgnored) {
                              ::opentelemetry::proto::trace::v1::Span::SPAN_KIND_SERVER, {}, {});
   EXPECT_EQ(sampling_result.decision, Decision::Drop);
   EXPECT_EQ(sampling_result.attributes->size(), 1);
+  EXPECT_EQ(sampling_result.attributes->size(), 2);
+  EXPECT_STREQ(
+      sampling_result.attributes->find("supportability.atm_sampling_ratio")->second.c_str(), "4");
+  EXPECT_STREQ(sampling_result.attributes->find("sampling.threshold")->second.c_str(),
+               "54043195528445952");
   // tracestate should be forwarded
   EXPECT_STREQ(sampling_result.tracestate.c_str(), dt_tracestate_ignored);
   // sampling decision from parent should be respected
@@ -144,6 +155,8 @@ TEST_F(DynatraceSamplerTest, TestWithDynatraceParentContextFromDifferentTenant)
   // sampling decision on tracestate should be ignored because it is from a different tenant.
   EXPECT_EQ(sampling_result.decision, Decision::RecordAndSample);
   EXPECT_EQ(sampling_result.attributes->size(), 1);
+  EXPECT_STREQ(
+      sampling_result.attributes->find("supportability.atm_sampling_ratio")->second.c_str(), "1");
   // new Dynatrace tag should be prepended, already existing tag should be kept
   const char* exptected =
       "5b3f9fed-980df25c@dt=fw4;0;0;0;0;0;0;95,6666ad40-980df25c@dt=fw4;4;4af38366;0;0;1;2;123;"