README.md

@@ -401,7 +401,7 @@ for i := 0; i < retries; i++ {
 
     // attempt to create topic prior to publishing the message
     err = w.WriteMessages(ctx, messages...)
-    if errors.Is(err, LeaderNotAvailable) || errors.Is(err, context.DeadlineExceeded) {
+    if errors.Is(err, kafka.LeaderNotAvailable) || errors.Is(err, context.DeadlineExceeded) {
         time.Sleep(time.Millisecond * 250)
         continue
     }

balancer.go

@@ -36,11 +36,14 @@ func (f BalancerFunc) Balance(msg Message, partitions ...int) int {
 }
 
 // RoundRobin is an Balancer implementation that equally distributes messages
-// across all available partitions.
+// across all available partitions.  It can take an optional chunk size to send
+// ChunkSize messages to the same partition before moving to the next partition.
+// This can be used to improve batch sizes.
 type RoundRobin struct {
+	ChunkSize int
 	// Use a 32 bits integer so RoundRobin values don't need to be aligned to
 	// apply atomic increments.
-	offset uint32
+	counter uint32
 }
 
 // Balance satisfies the Balancer interface.
@@ -49,8 +52,14 @@ func (rr *RoundRobin) Balance(msg Message, partitions ...int) int {
 }
 
 func (rr *RoundRobin) balance(partitions []int) int {
-	length := uint32(len(partitions))
-	offset := atomic.AddUint32(&rr.offset, 1) - 1
+	if rr.ChunkSize < 1 {
+		rr.ChunkSize = 1
+	}
+
+	length := len(partitions)
+	counterNow := atomic.LoadUint32(&rr.counter)
+	offset := int(counterNow / uint32(rr.ChunkSize))
+	atomic.AddUint32(&rr.counter, 1)
 	return partitions[offset%length]
 }
 
@@ -122,7 +131,7 @@ var (
 //
 // The logic to calculate the partition is:
 //
-// 		hasher.Sum32() % len(partitions) => partition
+//	hasher.Sum32() % len(partitions) => partition
 //
 // By default, Hash uses the FNV-1a algorithm.  This is the same algorithm used
 // by the Sarama Producer and ensures that messages produced by kafka-go will
@@ -173,7 +182,7 @@ func (h *Hash) Balance(msg Message, partitions ...int) int {
 //
 // The logic to calculate the partition is:
 //
-//      (int32(hasher.Sum32()) & 0x7fffffff) % len(partitions) => partition
+//	(int32(hasher.Sum32()) & 0x7fffffff) % len(partitions) => partition
 //
 // By default, ReferenceHash uses the FNV-1a algorithm. This is the same algorithm as
 // the Sarama NewReferenceHashPartitioner and ensures that messages produced by kafka-go will

balancer_test.go

@@ -411,3 +411,68 @@ func TestLeastBytes(t *testing.T) {
 		})
 	}
 }
+
+func TestRoundRobin(t *testing.T) {
+	testCases := map[string]struct {
+		Partitions []int
+		ChunkSize  int
+	}{
+		"default - odd partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6},
+		},
+		"negative chunk size - odd partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6},
+			ChunkSize:  -1,
+		},
+		"0 chunk size - odd partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6},
+			ChunkSize:  0,
+		},
+		"5 chunk size - odd partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6},
+			ChunkSize:  5,
+		},
+		"12 chunk size - odd partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6},
+			ChunkSize:  12,
+		},
+		"default - even partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6, 7},
+		},
+		"negative chunk size - even partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6, 7},
+			ChunkSize:  -1,
+		},
+		"0 chunk size - even partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6, 7},
+			ChunkSize:  0,
+		},
+		"5 chunk size - even partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6, 7},
+			ChunkSize:  5,
+		},
+		"12 chunk size - even partition count": {
+			Partitions: []int{0, 1, 2, 3, 4, 5, 6, 7},
+			ChunkSize:  12,
+		},
+	}
+	for label, test := range testCases {
+		t.Run(label, func(t *testing.T) {
+			lb := &RoundRobin{ChunkSize: test.ChunkSize}
+			msg := Message{}
+			var partition int
+			var i int
+			expectedChunkSize := test.ChunkSize
+			if expectedChunkSize < 1 {
+				expectedChunkSize = 1
+			}
+			partitions := test.Partitions
+			for i = 0; i < 50; i++ {
+				partition = lb.Balance(msg, partitions...)
+				if partition != i/expectedChunkSize%len(partitions) {
+					t.Error("Returned partition", partition, "expecting", i/expectedChunkSize%len(partitions))
+				}
+			}
+		})
+	}
+}