Fix DeletePartialMatch deleting unrelated metrics on hash collision

prometheus/vec.go

@@ -416,31 +416,30 @@ func (m *metricMap) deleteByLabels(labels Labels, curry []curriedLabelValue) int
 	var numDeleted int
 
 	for h, metrics := range m.metrics {
-		i := findMetricWithPartialLabels(m.desc, metrics, labels, curry)
-		if i >= len(metrics) {
-			// Didn't find matching labels in this metric slice.
-			continue
+		remaining := metrics[:0]
+		for _, metric := range metrics {
+			if matchPartialLabels(m.desc, metric.values, labels, curry) {
+				numDeleted++
+				continue
+			}
+			remaining = append(remaining, metric)
+		}
+		// Clear the tail of the backing array so deleted metrics don't
+		// stay reachable (and hence unable to be garbage collected)
+		// through the array's spare capacity.
+		for i := len(remaining); i < len(metrics); i++ {
+			metrics[i] = metricWithLabelValues{}
+		}
+		if len(remaining) == 0 {
+			delete(m.metrics, h)
+		} else {
+			m.metrics[h] = remaining
 		}
-		delete(m.metrics, h)
-		numDeleted++
 	}
 
 	return numDeleted
 }
 
-// findMetricWithPartialLabel returns the index of the matching metric or
-// len(metrics) if not found.
-func findMetricWithPartialLabels(
-	desc *Desc, metrics []metricWithLabelValues, labels Labels, curry []curriedLabelValue,
-) int {
-	for i, metric := range metrics {
-		if matchPartialLabels(desc, metric.values, labels, curry) {
-			return i
-		}
-	}
-	return len(metrics)
-}
-
 // indexOf searches the given slice of strings for the target string and returns
 // the index or len(items) as well as a boolean whether the search succeeded.
 func indexOf(target string, items []string) (int, bool) {

prometheus/vec_test.go

@@ -166,6 +166,19 @@ func TestDeletePartialMatch(t *testing.T) {
 	testDeletePartialMatch(t, vec)
 }
 
+func TestDeletePartialMatchWithCollisions(t *testing.T) {
+	vec := NewGaugeVec(
+		GaugeOpts{
+			Name: "test",
+			Help: "helpless",
+		},
+		[]string{"l1", "l2", "l3"},
+	)
+	vec.hashAdd = func(h uint64, s string) uint64 { return 1 }
+	vec.hashAddByte = func(h uint64, b byte) uint64 { return 1 }
+	testDeletePartialMatch(t, vec)
+}
+
 func TestDeletePartialMatchWithConstraints(t *testing.T) {
 	vec := V2.NewGaugeVec(GaugeVecOpts{
 		GaugeOpts{