Switches to the median over all DC nodes with known coordinates.

consul/rtt.go

@@ -223,23 +223,22 @@ func getDatacenterDistance(s serfer, dc string) (float64, error) {
 		return 0.0, err
 	}
 
-	// Fetch all the nodes in the DC.
+	// Fetch all the nodes in the DC and record their distance, if available.
 	nodes := s.GetNodesForDatacenter(dc)
-	subvec := make([]float64, len(nodes))
-	for j, node := range nodes {
+	subvec := make([]float64, 0, len(nodes))
+	for _, node := range nodes {
 		if other, ok := s.GetCachedCoordinate(node); ok {
-			subvec[j] = computeDistance(coord, other)
-		} else {
-			subvec[j] = computeDistance(coord, nil)
+			subvec = append(subvec, computeDistance(coord, other))
 		}
 	}
 
 	// Compute the median by sorting and taking the middle item.
-	sort.Float64s(subvec)
 	if len(subvec) > 0 {
+		sort.Float64s(subvec)
 		return subvec[len(subvec)/2], nil
 	}
 
+	// Return the default infinity value.
 	return computeDistance(coord, nil), nil
 }
 

consul/rtt_test.go

@@ -337,12 +337,13 @@ func TestRtt_getDatacenterDistance(t *testing.T) {
 	}
 
 	// Check the more interesting median case, note that there's a mystery
-	// node4 in there that should make the distances sort like this:
+	// node4 in there that should be excluded to make the distances sort
+	// like this:
 	//
-	// [0] node3 (0.005), [1] node1 (0.007), [2] node2 (0.008), [3] node4 (+Inf)
+	// [0] node3 (0.005), [1] node1 (0.007), [2] node2 (0.008)
 	//
-	// So the median should be at index 4 / 2 = 2 -> 0.008.
-	if dist, err := getDatacenterDistance(s, "dc1"); err != nil || dist != 0.008 {
+	// So the median should be at index 3 / 2 = 1 -> 0.007.
+	if dist, err := getDatacenterDistance(s, "dc1"); err != nil || dist != 0.007 {
 		t.Fatalf("bad: %v err: %v", dist, err)
 	}
 }