implement create topic

weed/mq/balancer/allocate.go

@@ -3,18 +3,50 @@ package balancer
 import (
 	cmap "github.com/orcaman/concurrent-map/v2"
 	"github.com/seaweedfs/seaweedfs/weed/pb/mq_pb"
+	"math/rand"
 )
 
 func allocateTopicPartitions(brokers cmap.ConcurrentMap[string, *BrokerStats], partitionCount int) (assignments []*mq_pb.BrokerPartitionAssignment) {
-	return []*mq_pb.BrokerPartitionAssignment{
-		{
-			LeaderBroker:    "localhost:17777",
-			FollowerBrokers: []string{"localhost:17777"},
+	// divide the ring into partitions
+	rangeSize := MaxPartitionCount / partitionCount
+	for i := 0; i < partitionCount; i++ {
+		assignment := &mq_pb.BrokerPartitionAssignment{
 			Partition: &mq_pb.Partition{
 				RingSize:   MaxPartitionCount,
-				RangeStart: 0,
-				RangeStop:  MaxPartitionCount,
+				RangeStart: int32(i * rangeSize),
+				RangeStop:  int32((i + 1) * rangeSize),
 			},
-		},
+		}
+		if i == partitionCount-1 {
+			assignment.Partition.RangeStop = MaxPartitionCount
+		}
+		assignments = append(assignments, assignment)
 	}
+
+	// pick the brokers
+	pickedBrokers := pickBrokers(brokers, partitionCount)
+
+	// assign the partitions to brokers
+	for i, assignment := range assignments {
+		assignment.LeaderBroker = pickedBrokers[i]
+	}
+	return
+}
+
+// for now: randomly pick brokers
+// TODO pick brokers based on the broker stats
+func pickBrokers(brokers cmap.ConcurrentMap[string, *BrokerStats], count int) []string {
+	candidates := make([]string, 0, brokers.Count())
+	for brokerStatsItem := range brokers.IterBuffered() {
+		candidates = append(candidates, brokerStatsItem.Key)
+	}
+	pickedBrokers := make([]string, 0, count)
+	for i := 0; i < count; i++ {
+		p := rand.Int() % len(candidates)
+		if p < 0 {
+			p = -p
+		}
+		pickedBrokers = append(pickedBrokers, candidates[p])
+	}
+	return pickedBrokers
 }