raft: add MaxInflightBytes to Config

This commit introduces the max inflight bytes setting at the Config level, and
tests that raft flow control honours it.

Signed-off-by: Pavel Kalinnikov <pavel@cockroachlabs.com>

raft/raft.go

@@ -160,6 +160,16 @@ type Config struct {
 	// overflowing that sending buffer. TODO (xiangli): feedback to application to
 	// limit the proposal rate?
 	MaxInflightMsgs int
+	// MaxInflightBytes limits the number of in-flight bytes in append messages.
+	// Complements MaxInflightMsgs. Ignored if zero.
+	//
+	// This effectively bounds the bandwidth-delay product. Note that especially
+	// in high-latency deployments setting this too low can lead to a dramatic
+	// reduction in throughput. For example, with a peer that has a round-trip
+	// latency of 100ms to the leader and this setting is set to 1 MB, there is a
+	// throughput limit of 10 MB/s for this group. With RTT of 400ms, this drops
+	// to 2.5 MB/s. See Little's law to understand the maths behind.
+	MaxInflightBytes uint64
 
 	// CheckQuorum specifies if the leader should check quorum activity. Leader
 	// steps down when quorum is not active for an electionTimeout.
@@ -228,6 +238,11 @@ func (c *Config) validate() error {
 	if c.MaxInflightMsgs <= 0 {
 		return errors.New("max inflight messages must be greater than 0")
 	}
+	if c.MaxInflightBytes == 0 {
+		c.MaxInflightBytes = noLimit
+	} else if c.MaxInflightBytes < c.MaxSizePerMsg {
+		return errors.New("max inflight bytes must be >= max message size")
+	}
 
 	if c.Logger == nil {
 		c.Logger = getLogger()
@@ -332,7 +347,7 @@ func newRaft(c *Config) *raft {
 		raftLog:                   raftlog,
 		maxMsgSize:                c.MaxSizePerMsg,
 		maxUncommittedSize:        c.MaxUncommittedEntriesSize,
-		prs:                       tracker.MakeProgressTracker(c.MaxInflightMsgs, 0), // TODO: set maxBytes
+		prs:                       tracker.MakeProgressTracker(c.MaxInflightMsgs, c.MaxInflightBytes),
 		electionTimeout:           c.ElectionTick,
 		heartbeatTimeout:          c.HeartbeatTick,
 		logger:                    c.Logger,
@@ -484,8 +499,7 @@ func (r *raft) maybeSendAppend(to uint64, sendIfEmpty bool) bool {
 
 	// Send the actual MsgApp otherwise, and update the progress accordingly.
 	next := pr.Next // save Next for later, as the progress update can change it
-	// TODO(pavelkalinnikov): set bytes to sum(Entries[].Size())
+	if err := pr.UpdateOnEntriesSend(len(ents), payloadsSize(ents), next); err != nil {
-	if err := pr.UpdateOnEntriesSend(len(ents), 0 /* bytes */, next); err != nil {
 		r.logger.Panicf("%x: %v", r.id, err)
 	}
 	r.send(pb.Message{

raft/raft_test.go

@@ -130,6 +130,7 @@ func TestProgressFlowControl(t *testing.T) {
 	cfg := newTestConfig(1, 5, 1, newTestMemoryStorage(withPeers(1, 2)))
 	cfg.MaxInflightMsgs = 3
 	cfg.MaxSizePerMsg = 2048
+	cfg.MaxInflightBytes = 9000 // A little over MaxInflightMsgs * MaxSizePerMsg.
 	r := newRaft(cfg)
 	r.becomeCandidate()
 	r.becomeLeader()
@@ -140,7 +141,12 @@ func TestProgressFlowControl(t *testing.T) {
 	// While node 2 is in probe state, propose a bunch of entries.
 	r.prs.Progress[2].BecomeProbe()
 	blob := []byte(strings.Repeat("a", 1000))
-	for i := 0; i < 10; i++ {
+	large := []byte(strings.Repeat("b", 5000))
+	for i := 0; i < 22; i++ {
+		blob := blob
+		if i >= 10 && i < 16 { // Temporarily send large messages.
+			blob = large
+		}
 		r.Step(pb.Message{From: 1, To: 1, Type: pb.MsgProp, Entries: []pb.Entry{{Data: blob}}})
 	}
 
@@ -158,40 +164,40 @@ func TestProgressFlowControl(t *testing.T) {
 		t.Fatalf("unexpected entry sizes: %v", ms[0].Entries)
 	}
 
-	// When this append is acked, we change to replicate state and can
+	ackAndVerify := func(index uint64, expEntries ...int) uint64 {
-	// send multiple messages at once.
+		r.Step(pb.Message{From: 2, To: 1, Type: pb.MsgAppResp, Index: index})
-	r.Step(pb.Message{From: 2, To: 1, Type: pb.MsgAppResp, Index: ms[0].Entries[1].Index})
+		ms := r.readMessages()
-	ms = r.readMessages()
+		if got, want := len(ms), len(expEntries); got != want {
-	if len(ms) != 3 {
+			t.Fatalf("expected %d messages, got %d", want, got)
-		t.Fatalf("expected 3 messages, got %d", len(ms))
-	}
-	for i, m := range ms {
-		if m.Type != pb.MsgApp {
-			t.Errorf("%d: expected MsgApp, got %s", i, m.Type)
 		}
-		if len(m.Entries) != 2 {
+		for i, m := range ms {
-			t.Errorf("%d: expected 2 entries, got %d", i, len(m.Entries))
+			if got, want := m.Type, pb.MsgApp; got != want {
+				t.Errorf("%d: expected MsgApp, got %s", i, got)
+			}
+			if got, want := len(m.Entries), expEntries[i]; got != want {
+				t.Errorf("%d: expected %d entries, got %d", i, want, got)
+			}
 		}
+		last := ms[len(ms)-1].Entries
+		if len(last) == 0 {
+			return index
+		}
+		return last[len(last)-1].Index
 	}
 
-	// Ack all three of those messages together and get the last two
+	// When this append is acked, we change to replicate state and can
-	// messages (containing three entries).
+	// send multiple messages at once.
-	r.Step(pb.Message{From: 2, To: 1, Type: pb.MsgAppResp, Index: ms[2].Entries[1].Index})
+	index := ackAndVerify(ms[0].Entries[1].Index, 2, 2, 2)
-	ms = r.readMessages()
+	// Ack all three of those messages together and get another 3 messages. The
-	if len(ms) != 2 {
+	// third message contains a single large entry, in contrast to 2 before.
-		t.Fatalf("expected 2 messages, got %d", len(ms))
+	index = ackAndVerify(index, 2, 1, 1)
-	}
+	// All subsequent messages contain one large entry, and we cap at 2 messages
-	for i, m := range ms {
+	// because it overflows MaxInflightBytes.
-		if m.Type != pb.MsgApp {
+	index = ackAndVerify(index, 1, 1)
-			t.Errorf("%d: expected MsgApp, got %s", i, m.Type)
+	index = ackAndVerify(index, 1, 1)
-		}
+	// Start getting small messages again.
-	}
+	index = ackAndVerify(index, 1, 2, 2)
-	if len(ms[0].Entries) != 2 {
+	ackAndVerify(index, 2)
-		t.Errorf("%d: expected 2 entries, got %d", 0, len(ms[0].Entries))
-	}
-	if len(ms[1].Entries) != 1 {
-		t.Errorf("%d: expected 1 entry, got %d", 1, len(ms[1].Entries))
-	}
 }
 
 func TestUncommittedEntryLimit(t *testing.T) {

raft/tracker/progress_test.go

@@ -53,9 +53,9 @@ func TestProgressIsPaused(t *testing.T) {
 	}
 	for i, tt := range tests {
 		p := &Progress{
-			State:     tt.state,
+			State:            tt.state,
 			MsgAppFlowPaused: tt.paused,
-			Inflights: NewInflights(256, 0),
+			Inflights:        NewInflights(256, 0),
 		}
 		assert.Equal(t, tt.w, p.IsPaused(), i)
 	}