[processor/tailsampling] Late span age histogram should include sampled traces (open-telemetry#37180)

Currently, the [late span age
histogram](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/981e9f5cc58149ea37c8909a4a6eb30faee96351/processor/tailsamplingprocessor/internal/metadata/generated_telemetry.go#L106-L110)
only includes non-sampled traces. The histogram should also include
sampled traces. This pull request includes anything with a decision
time.

_Note: The decision cache still wrecks it 😅_

---------

Signed-off-by: Sean Porter <[email protected]>
Co-authored-by: Juraci Paixão Kröhling <[email protected]>

Author: 2 people

.chloggen/tailsamplingprocessor-late-span-age-histogram.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: tailsamplingprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Late span age histogram should include sampled traces.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [37180]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

processor/tailsamplingprocessor/processor.go

@@ -518,11 +518,14 @@ func (tsp *tailSamplingSpanProcessor) processTraces(resourceSpans ptrace.Resourc
 				tsp.releaseSampledTrace(tsp.ctx, id, traceTd)
 			case sampling.NotSampled:
 				tsp.nonSampledIDCache.Put(id, true)
-				tsp.telemetry.ProcessorTailSamplingSamplingLateSpanAge.Record(tsp.ctx, int64(time.Since(actualData.DecisionTime)/time.Second))
 			default:
 				tsp.logger.Warn("Encountered unexpected sampling decision",
 					zap.Int("decision", int(finalDecision)))
 			}
+
+			if !actualData.DecisionTime.IsZero() {
+				tsp.telemetry.ProcessorTailSamplingSamplingLateSpanAge.Record(tsp.ctx, int64(time.Since(actualData.DecisionTime)/time.Second))
+			}
 		}
 	}
 

processor/tailsamplingprocessor/processor_telemetry_test.go

@@ -455,10 +455,10 @@ func TestProcessorTailSamplingSamplingLateSpanAge(t *testing.T) {
 		PolicyCfgs: []PolicyCfg{
 			{
 				sharedPolicyCfg: sharedPolicyCfg{
-					Name: "never-sample",
+					Name: "sample-half",
 					Type: Probabilistic,
 					ProbabilisticCfg: ProbabilisticCfg{
-						SamplingPercentage: 0,
+						SamplingPercentage: 50,
 					},
 				},
 			},
@@ -476,22 +476,24 @@ func TestProcessorTailSamplingSamplingLateSpanAge(t *testing.T) {
 	err = proc.Start(context.Background(), componenttest.NewNopHost())
 	require.NoError(t, err)
 
-	traces := simpleTraces()
-	traceID := traces.ResourceSpans().At(0).ScopeSpans().AppendEmpty().Spans().AppendEmpty().TraceID()
-
-	lateSpan := ptrace.NewTraces()
-	lateSpan.ResourceSpans().AppendEmpty().ScopeSpans().AppendEmpty().Spans().AppendEmpty().SetTraceID(traceID)
-
 	// test
-	err = proc.ConsumeTraces(context.Background(), traces)
-	require.NoError(t, err)
+	traceIDs, batches := generateIDsAndBatches(10)
+	for _, batch := range batches {
+		err = proc.ConsumeTraces(context.Background(), batch)
+		require.NoError(t, err)
+	}
 
 	tsp := proc.(*tailSamplingSpanProcessor)
 	tsp.policyTicker.OnTick() // the first tick always gets an empty batch
 	tsp.policyTicker.OnTick()
 
-	err = proc.ConsumeTraces(context.Background(), lateSpan)
-	require.NoError(t, err)
+	for _, traceID := range traceIDs {
+		lateSpan := ptrace.NewTraces()
+		lateSpan.ResourceSpans().AppendEmpty().ScopeSpans().AppendEmpty().Spans().AppendEmpty().SetTraceID(traceID)
+
+		err = proc.ConsumeTraces(context.Background(), lateSpan)
+		require.NoError(t, err)
+	}
 
 	// verify
 	var md metricdata.ResourceMetrics
@@ -503,11 +505,22 @@ func TestProcessorTailSamplingSamplingLateSpanAge(t *testing.T) {
 		Unit:        "s",
 		Data: metricdata.Histogram[int64]{
 			Temporality: metricdata.CumulativeTemporality,
-			DataPoints:  []metricdata.HistogramDataPoint[int64]{{}},
+			DataPoints: []metricdata.HistogramDataPoint[int64]{
+				{
+					Count:        10,
+					Bounds:       []float64{0, 5, 10, 25, 50, 75, 100, 250, 500, 750, 1000, 2500, 5000, 7500, 10000},
+					BucketCounts: []uint64{10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
+					Min:          metricdata.NewExtrema[int64](0),
+					Max:          metricdata.NewExtrema[int64](0),
+					Sum:          0,
+				},
+			},
 		},
 	}
+
 	got := s.getMetric(m.Name, md)
-	metricdatatest.AssertEqual(t, m, got, metricdatatest.IgnoreTimestamp(), metricdatatest.IgnoreValue())
+
+	metricdatatest.AssertEqual(t, m, got, metricdatatest.IgnoreTimestamp())
 }
 
 type testTelemetry struct {