Handle empty result sets in merge logic

Fixes #329
jacksontj · Jul 20, 2020 · 30fc828 · 30fc828
1 parent c8af25e
commit 30fc828
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diff --git a/pkg/promhttputil/merge.go b/pkg/promhttputil/merge.go
@@ -181,6 +181,13 @@ func MergeSampleStream(antiAffinityBuffer model.Time, a, b *model.SampleStream)
 		return nil, fmt.Errorf("cannot merge mismatch fingerprints")
 	}
 
+	// if either set of values are empty, return the one with data
+	if len(a.Values) == 0 {
+		return b, nil
+	} else if len(b.Values) == 0 {
+		return a, nil
+	}
+
 	// TODO: really there should be a library method for this in prometheus IMO
 	// At this point we have 2 sorted lists of datapoints which we need to merge
 	newValues := make([]model.SamplePair, 0, len(a.Values))

diff --git a/pkg/promhttputil/merge_test.go b/pkg/promhttputil/merge_test.go
@@ -509,6 +509,64 @@ func TestMergeValues(t *testing.T) {
 			}),
 			antiAffinity: model.Time(2),
 		},
+
+		{
+			name: "Matrix merge empty A",
+			a: model.Matrix([]*model.SampleStream{
+				{
+					model.Metric(model.LabelSet{model.MetricNameLabel: model.LabelValue("hosta")}),
+					[]model.SamplePair{},
+				},
+			}),
+			b: model.Matrix([]*model.SampleStream{
+				{
+					model.Metric(model.LabelSet{model.MetricNameLabel: model.LabelValue("hosta")}),
+					[]model.SamplePair{{
+						model.Time(100),
+						model.SampleValue(10),
+					}},
+				},
+			}),
+			r: model.Matrix([]*model.SampleStream{
+				{
+					model.Metric(model.LabelSet{model.MetricNameLabel: model.LabelValue("hosta")}),
+					[]model.SamplePair{{
+						model.Time(100),
+						model.SampleValue(10),
+					}},
+				},
+			}),
+			antiAffinity: model.Time(2),
+		},
+
+		{
+			name: "Matrix merge empty A",
+			a: model.Matrix([]*model.SampleStream{
+				{
+					model.Metric(model.LabelSet{model.MetricNameLabel: model.LabelValue("hosta")}),
+					[]model.SamplePair{{
+						model.Time(100),
+						model.SampleValue(10),
+					}},
+				},
+			}),
+			b: model.Matrix([]*model.SampleStream{
+				{
+					model.Metric(model.LabelSet{model.MetricNameLabel: model.LabelValue("hosta")}),
+					[]model.SamplePair{},
+				},
+			}),
+			r: model.Matrix([]*model.SampleStream{
+				{
+					model.Metric(model.LabelSet{model.MetricNameLabel: model.LabelValue("hosta")}),
+					[]model.SamplePair{{
+						model.Time(100),
+						model.SampleValue(10),
+					}},
+				},
+			}),
+			antiAffinity: model.Time(2),
+		},
 	}
 
 	for _, test := range tests {