edge cases for broker assignment

weed/mq/pub_balancer/allocate.go

@@ -27,13 +27,8 @@ func AllocateTopicPartitions(brokers cmap.ConcurrentMap[string, *BrokerStats], p
 		assignments = append(assignments, assignment)
 	}
 
-	// pick the brokers
-	pickedBrokers := pickBrokers(brokers, partitionCount)
+	EnsureAssignmentsToActiveBrokers(brokers, 1, assignments)
 
-	// assign the partitions to brokers
-	for i, assignment := range assignments {
-		assignment.LeaderBroker = pickedBrokers[i]
-	}
 	glog.V(0).Infof("allocate topic partitions %d: %v", len(assignments), assignments)
 	return
 }
@@ -91,6 +86,8 @@ func pickBrokersExcluded(brokers []string, count int, excludedLeadBroker string,
 
 // EnsureAssignmentsToActiveBrokers ensures the assignments are assigned to active brokers
 func EnsureAssignmentsToActiveBrokers(activeBrokers cmap.ConcurrentMap[string, *BrokerStats], followerCount int, assignments []*mq_pb.BrokerPartitionAssignment) (hasChanges bool) {
+	glog.V(0).Infof("EnsureAssignmentsToActiveBrokers: activeBrokers: %v, followerCount: %d, assignments: %v", activeBrokers.Count(), followerCount, assignments)
+
 	candidates := make([]string, 0, activeBrokers.Count())
 	for brokerStatsItem := range activeBrokers.IterBuffered() {
 		candidates = append(candidates, brokerStatsItem.Key)
@@ -122,10 +119,12 @@ func EnsureAssignmentsToActiveBrokers(activeBrokers cmap.ConcurrentMap[string, *
 			pickedBrokers := pickBrokersExcluded(candidates, count, assignment.LeaderBroker, assignment.FollowerBrokers)
 			i := 0
 			if assignment.LeaderBroker == "" {
+				if i < len(pickedBrokers) {
 					assignment.LeaderBroker = pickedBrokers[i]
 					i++
 					hasChanges = true
 				}
+			}
 
 			hasEmptyFollowers := false
 			j := 0
@@ -158,5 +157,6 @@ func EnsureAssignmentsToActiveBrokers(activeBrokers cmap.ConcurrentMap[string, *
 
 	}
 
+	glog.V(0).Infof("EnsureAssignmentsToActiveBrokers: activeBrokers: %v, followerCount: %d, assignments: %v hasChanges: %v", activeBrokers.Count(), followerCount, assignments, hasChanges)
 	return
 }

weed/mq/pub_balancer/allocate_test.go

@@ -209,6 +209,20 @@ func TestEnsureAssignmentsToActiveBrokersX(t *testing.T) {
 			},
 			hasChanges: false,
 		},
+		{
+			name: "test low active brokers with one follower",
+			args: args{
+				activeBrokers: lowActiveBrokers,
+				followerCount: 1,
+				assignments:   []*mq_pb.BrokerPartitionAssignment{
+					{
+						LeaderBroker: "localhost:1",
+						Partition: &mq_pb.Partition{},
+					},
+				},
+			},
+			hasChanges: true,
+		},
 		{
 			name: "test single active broker",
 			args: args{