[processor/cumulativetodelta]: exclude the first point after a restar…

…t in monotonic sums (#18298)

fix: omit point after a restart in monotonic sums

.chloggen/cumulativetodelta-drop-first-datapoint-after-restart.yaml

@@ -0,0 +1,16 @@
+# 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: cumulativetodeltaprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: exclude the first point after a restart in monotonic sums
+
+# One or more tracking issues related to the change
+issues: [17190, 18053]
+
+# (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:

processor/cumulativetodeltaprocessor/internal/tracking/tracker.go

@@ -127,7 +127,7 @@ func (t *MetricTracker) Convert(in MetricPoint) (out DeltaValue, valid bool) {
 
 			// Detect reset (non-monotonic sums are not converted)
 			if value < prevValue {
-				delta = value
+				valid = false
 			}
 
 			out.FloatValue = delta
@@ -138,7 +138,7 @@ func (t *MetricTracker) Convert(in MetricPoint) (out DeltaValue, valid bool) {
 
 			// Detect reset (non-monotonic sums are not converted)
 			if value < prevValue {
-				delta = value
+				valid = false
 			}
 
 			out.IntValue = delta

processor/cumulativetodeltaprocessor/internal/tracking/tracker_test.go

@@ -50,7 +50,7 @@ func TestMetricTracker_Convert(t *testing.T) {
 		noOut   bool
 	}{
 		{
-			name: "Initial Value not recorded",
+			name: "Initial Value Omitted",
 			value: ValuePoint{
 				ObservedTimestamp: 10,
 				FloatValue:        100.0,
@@ -59,7 +59,7 @@ func TestMetricTracker_Convert(t *testing.T) {
 			noOut: true,
 		},
 		{
-			name: "Higher Value Recorded",
+			name: "Higher Value Converted",
 			value: ValuePoint{
 				ObservedTimestamp: 50,
 				FloatValue:        225.0,
@@ -72,20 +72,16 @@ func TestMetricTracker_Convert(t *testing.T) {
 			},
 		},
 		{
-			name: "Lower Value Recorded - No Previous Offset",
+			name: "Lower Value not Converted - Restart",
 			value: ValuePoint{
 				ObservedTimestamp: 100,
 				FloatValue:        75.0,
 				IntValue:          75,
 			},
-			wantOut: DeltaValue{
-				StartTimestamp: 50,
-				FloatValue:     75.0,
-				IntValue:       75,
-			},
+			noOut: true,
 		},
 		{
-			name: "Record delta above first recorded value",
+			name: "Convert delta above previous not Converted Value",
 			value: ValuePoint{
 				ObservedTimestamp: 150,
 				FloatValue:        300.0,
@@ -98,11 +94,11 @@ func TestMetricTracker_Convert(t *testing.T) {
 			},
 		},
 		{
-			name: "Lower Value Recorded - Previous Offset Recorded",
+			name: "Higher Value Converted - Previous Offset Recorded",
 			value: ValuePoint{
 				ObservedTimestamp: 200,
-				FloatValue:        25.0,
-				IntValue:          25,
+				FloatValue:        325.0,
+				IntValue:          325,
 			},
 			wantOut: DeltaValue{
 				StartTimestamp: 150,

processor/cumulativetodeltaprocessor/processor_test.go

@@ -425,6 +425,28 @@ func TestCumulativeToDeltaProcessor(t *testing.T) {
 				isMonotonic:  []bool{true, true},
 			}),
 		},
+		{
+			name: "cumulative_to_delta_restart_detected",
+			include: MatchMetrics{
+				Metrics: []string{".*"},
+				Config: filterset.Config{
+					MatchType:    "regexp",
+					RegexpConfig: nil,
+				},
+			},
+			inMetrics: generateTestSumMetrics(testSumMetric{
+				metricNames:  []string{"metric_1"},
+				metricValues: [][]float64{{100, 105, 120, 100, 110}},
+				isCumulative: []bool{true},
+				isMonotonic:  []bool{true},
+			}),
+			outMetrics: generateTestSumMetrics(testSumMetric{
+				metricNames:  []string{"metric_1"},
+				metricValues: [][]float64{{5, 15, 10}},
+				isCumulative: []bool{false},
+				isMonotonic:  []bool{true},
+			}),
+		},
 	}
 
 	for _, test := range testCases {