diff --git a/raft.go b/raft.go
index a2e5ad0f..1b52a163 100644
--- a/raft.go
+++ b/raft.go
@@ -827,7 +827,7 @@ func (r *raft) appendEntry(es ...pb.Entry) (accepted bool) {
 	//  if r.maybeCommit() {
 	//  	r.bcastAppend()
 	//  }
-	r.send(pb.Message{To: r.id, Type: pb.MsgAppResp, Index: li})
+	r.send(pb.Message{To: r.id, Type: pb.MsgAppResp, Index: li, Commit: r.raftLog.committed})
 	return true
 }
 
@@ -1493,7 +1493,9 @@ func stepLeader(r *raft, m pb.Message) error {
 			// equals pr.Match we know we don't m.Index+1 in our log, so moving
 			// back to replicating state is not useful; besides pr.PendingSnapshot
 			// would prevent it.
-			if pr.MaybeUpdate(m.Index) || (pr.Match == m.Index && pr.State == tracker.StateProbe) {
+			updated := pr.MaybeUpdate(m.Index)
+			pr.UpdateCommit(m.Commit)
+			if updated || (pr.Match == m.Index && pr.State == tracker.StateProbe) {
 				switch {
 				case pr.State == tracker.StateProbe:
 					pr.BecomeReplicate()
@@ -1765,12 +1767,12 @@ func (r *raft) handleAppendEntries(m pb.Message) {
 	// message, and validate it before taking any action (e.g. bumping term).
 	a := logSliceFromMsgApp(&m)
 
-	if a.prev.index < r.raftLog.committed {
-		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.raftLog.committed})
+	if commit := r.raftLog.committed; a.prev.index < commit {
+		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.raftLog.committed, Commit: commit})
 		return
 	}
 	if mlastIndex, ok := r.raftLog.maybeAppend(a, m.Commit); ok {
-		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: mlastIndex})
+		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: mlastIndex, Commit: r.raftLog.committed})
 		return
 	}
 	r.logger.Debugf("%x [logterm: %d, index: %d] rejected MsgApp [logterm: %d, index: %d] from %x",
diff --git a/raft_paper_test.go b/raft_paper_test.go
index eff31f63..5c72c280 100644
--- a/raft_paper_test.go
+++ b/raft_paper_test.go
@@ -28,6 +28,7 @@ package raft
 
 import (
 	"fmt"
+	"github.com/stretchr/testify/require"
 	"reflect"
 	"sort"
 	"testing"
@@ -606,20 +607,21 @@ func TestFollowerCheckMsgApp(t *testing.T) {
 		term        uint64
 		index       uint64
 		windex      uint64
+		wcommit     uint64
 		wreject     bool
 		wrejectHint uint64
 		wlogterm    uint64
 	}{
 		// match with committed entries
-		{0, 0, 1, false, 0, 0},
-		{ents[0].Term, ents[0].Index, 1, false, 0, 0},
+		{0, 0, 1, 1, false, 0, 0},
+		{ents[0].Term, ents[0].Index, 1, 1, false, 0, 0},
 		// match with uncommitted entries
-		{ents[1].Term, ents[1].Index, 2, false, 0, 0},
+		{ents[1].Term, ents[1].Index, 2, 1, false, 0, 0},
 
 		// unmatch with existing entry
-		{ents[0].Term, ents[1].Index, ents[1].Index, true, 1, 1},
+		{ents[0].Term, ents[1].Index, ents[1].Index, 0, true, 1, 1},
 		// unexisting entry
-		{ents[1].Term + 1, ents[1].Index + 1, ents[1].Index + 1, true, 2, 2},
+		{ents[1].Term + 1, ents[1].Index + 1, ents[1].Index + 1, 0, true, 2, 2},
 	}
 	for i, tt := range tests {
 		storage := newTestMemoryStorage(withPeers(1, 2, 3))
@@ -630,13 +632,11 @@ func TestFollowerCheckMsgApp(t *testing.T) {
 
 		r.Step(pb.Message{From: 2, To: 1, Type: pb.MsgApp, Term: 2, LogTerm: tt.term, Index: tt.index})
 
-		msgs := r.readMessages()
-		wmsgs := []pb.Message{
-			{From: 1, To: 2, Type: pb.MsgAppResp, Term: 2, Index: tt.windex, Reject: tt.wreject, RejectHint: tt.wrejectHint, LogTerm: tt.wlogterm},
-		}
-		if !reflect.DeepEqual(msgs, wmsgs) {
-			t.Errorf("#%d: msgs = %+v, want %+v", i, msgs, wmsgs)
+		wmsg := pb.Message{
+			From: 1, To: 2, Type: pb.MsgAppResp, Term: 2, Index: tt.windex, Commit: tt.wcommit,
+			Reject: tt.wreject, RejectHint: tt.wrejectHint, LogTerm: tt.wlogterm,
 		}
+		require.Equal(t, []pb.Message{wmsg}, r.readMessages(), "#%d", i)
 	}
 }
 
diff --git a/testdata/async_storage_writes.txt b/testdata/async_storage_writes.txt
index 02e59e5a..9434e6c0 100644
--- a/testdata/async_storage_writes.txt
+++ b/testdata/async_storage_writes.txt
@@ -90,7 +90,7 @@ stabilize
   1->2 MsgApp Term:1 Log:1/10 Commit:10 Entries:[1/11 EntryNormal ""]
   1->3 MsgApp Term:1 Log:1/10 Commit:10 Entries:[1/11 EntryNormal ""]
   1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/11 EntryNormal ""] Responses:[
-    1->1 MsgAppResp Term:1 Log:0/11
+    1->1 MsgAppResp Term:1 Log:0/11 Commit:10
     AppendThread->1 MsgStorageAppendResp Term:1 Log:1/11
   ]
 > 2 receiving messages
@@ -101,7 +101,7 @@ stabilize
   Processing:
   1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/11 EntryNormal ""]
   Responses:
-  1->1 MsgAppResp Term:1 Log:0/11
+  1->1 MsgAppResp Term:1 Log:0/11 Commit:10
   AppendThread->1 MsgStorageAppendResp Term:1 Log:1/11
 > 2 handling Ready
   Ready MustSync=true:
@@ -110,7 +110,7 @@ stabilize
   1/11 EntryNormal ""
   Messages:
   2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/11 EntryNormal ""] Responses:[
-    2->1 MsgAppResp Term:1 Log:0/11
+    2->1 MsgAppResp Term:1 Log:0/11 Commit:10
     AppendThread->2 MsgStorageAppendResp Term:1 Log:1/11
   ]
 > 3 handling Ready
@@ -120,27 +120,27 @@ stabilize
   1/11 EntryNormal ""
   Messages:
   3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/11 EntryNormal ""] Responses:[
-    3->1 MsgAppResp Term:1 Log:0/11
+    3->1 MsgAppResp Term:1 Log:0/11 Commit:10
     AppendThread->3 MsgStorageAppendResp Term:1 Log:1/11
   ]
 > 1 receiving messages
-  1->1 MsgAppResp Term:1 Log:0/11
+  1->1 MsgAppResp Term:1 Log:0/11 Commit:10
   AppendThread->1 MsgStorageAppendResp Term:1 Log:1/11
 > 2 processing append thread
   Processing:
   2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/11 EntryNormal ""]
   Responses:
-  2->1 MsgAppResp Term:1 Log:0/11
+  2->1 MsgAppResp Term:1 Log:0/11 Commit:10
   AppendThread->2 MsgStorageAppendResp Term:1 Log:1/11
 > 3 processing append thread
   Processing:
   3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/11 EntryNormal ""]
   Responses:
-  3->1 MsgAppResp Term:1 Log:0/11
+  3->1 MsgAppResp Term:1 Log:0/11 Commit:10
   AppendThread->3 MsgStorageAppendResp Term:1 Log:1/11
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/11
-  3->1 MsgAppResp Term:1 Log:0/11
+  2->1 MsgAppResp Term:1 Log:0/11 Commit:10
+  3->1 MsgAppResp Term:1 Log:0/11 Commit:10
 > 2 receiving messages
   AppendThread->2 MsgStorageAppendResp Term:1 Log:1/11
 > 3 receiving messages
@@ -177,7 +177,7 @@ stabilize
   1/11 EntryNormal ""
   Messages:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:11 Vote:1 Responses:[
-    2->1 MsgAppResp Term:1 Log:0/11
+    2->1 MsgAppResp Term:1 Log:0/11 Commit:11
   ]
   2->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/11 EntryNormal ""] Responses:[
     ApplyThread->2 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/11 EntryNormal ""]
@@ -189,7 +189,7 @@ stabilize
   1/11 EntryNormal ""
   Messages:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:11 Vote:1 Responses:[
-    3->1 MsgAppResp Term:1 Log:0/11
+    3->1 MsgAppResp Term:1 Log:0/11 Commit:11
   ]
   3->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/11 EntryNormal ""] Responses:[
     ApplyThread->3 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/11 EntryNormal ""]
@@ -200,12 +200,12 @@ stabilize
   Processing:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:11 Vote:1
   Responses:
-  2->1 MsgAppResp Term:1 Log:0/11
+  2->1 MsgAppResp Term:1 Log:0/11 Commit:11
 > 3 processing append thread
   Processing:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:11 Vote:1
   Responses:
-  3->1 MsgAppResp Term:1 Log:0/11
+  3->1 MsgAppResp Term:1 Log:0/11 Commit:11
 > 2 processing apply thread
   Processing:
   2->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/11 EntryNormal ""]
@@ -217,8 +217,8 @@ stabilize
   Responses:
   ApplyThread->3 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/11 EntryNormal ""]
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/11
-  3->1 MsgAppResp Term:1 Log:0/11
+  2->1 MsgAppResp Term:1 Log:0/11 Commit:11
+  3->1 MsgAppResp Term:1 Log:0/11 Commit:11
 > 2 receiving messages
   ApplyThread->2 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/11 EntryNormal ""]
 > 3 receiving messages
@@ -238,7 +238,7 @@ process-ready 1 2 3
   1->2 MsgApp Term:1 Log:1/11 Commit:11 Entries:[1/12 EntryNormal "prop_1"]
   1->3 MsgApp Term:1 Log:1/11 Commit:11 Entries:[1/12 EntryNormal "prop_1"]
   1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"] Responses:[
-    1->1 MsgAppResp Term:1 Log:0/12
+    1->1 MsgAppResp Term:1 Log:0/12 Commit:11
     AppendThread->1 MsgStorageAppendResp Term:1 Log:1/12
   ]
 > 2 handling Ready
@@ -261,7 +261,7 @@ process-ready 1 2 3
   1/12 EntryNormal "prop_1"
   Messages:
   2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"] Responses:[
-    2->1 MsgAppResp Term:1 Log:0/12
+    2->1 MsgAppResp Term:1 Log:0/12 Commit:11
     AppendThread->2 MsgStorageAppendResp Term:1 Log:1/12
   ]
 > 3 handling Ready
@@ -270,7 +270,7 @@ process-ready 1 2 3
   1/12 EntryNormal "prop_1"
   Messages:
   3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"] Responses:[
-    3->1 MsgAppResp Term:1 Log:0/12
+    3->1 MsgAppResp Term:1 Log:0/12 Commit:11
     AppendThread->3 MsgStorageAppendResp Term:1 Log:1/12
   ]
 
@@ -288,7 +288,7 @@ process-ready 1 2 3
   1->2 MsgApp Term:1 Log:1/12 Commit:11 Entries:[1/13 EntryNormal "prop_2"]
   1->3 MsgApp Term:1 Log:1/12 Commit:11 Entries:[1/13 EntryNormal "prop_2"]
   1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"] Responses:[
-    1->1 MsgAppResp Term:1 Log:0/13
+    1->1 MsgAppResp Term:1 Log:0/13 Commit:11
     AppendThread->1 MsgStorageAppendResp Term:1 Log:1/13
   ]
 > 2 handling Ready
@@ -311,7 +311,7 @@ process-ready 1 2 3
   1/13 EntryNormal "prop_2"
   Messages:
   2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"] Responses:[
-    2->1 MsgAppResp Term:1 Log:0/13
+    2->1 MsgAppResp Term:1 Log:0/13 Commit:11
     AppendThread->2 MsgStorageAppendResp Term:1 Log:1/13
   ]
 > 3 handling Ready
@@ -320,7 +320,7 @@ process-ready 1 2 3
   1/13 EntryNormal "prop_2"
   Messages:
   3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"] Responses:[
-    3->1 MsgAppResp Term:1 Log:0/13
+    3->1 MsgAppResp Term:1 Log:0/13 Commit:11
     AppendThread->3 MsgStorageAppendResp Term:1 Log:1/13
   ]
 
@@ -330,27 +330,27 @@ process-append-thread 1 2 3
   Processing:
   1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"]
   Responses:
-  1->1 MsgAppResp Term:1 Log:0/12
+  1->1 MsgAppResp Term:1 Log:0/12 Commit:11
   AppendThread->1 MsgStorageAppendResp Term:1 Log:1/12
 > 2 processing append thread
   Processing:
   2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"]
   Responses:
-  2->1 MsgAppResp Term:1 Log:0/12
+  2->1 MsgAppResp Term:1 Log:0/12 Commit:11
   AppendThread->2 MsgStorageAppendResp Term:1 Log:1/12
 > 3 processing append thread
   Processing:
   3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"]
   Responses:
-  3->1 MsgAppResp Term:1 Log:0/12
+  3->1 MsgAppResp Term:1 Log:0/12 Commit:11
   AppendThread->3 MsgStorageAppendResp Term:1 Log:1/12
 
 deliver-msgs 1 2 3
 ----
-1->1 MsgAppResp Term:1 Log:0/12
+1->1 MsgAppResp Term:1 Log:0/12 Commit:11
 AppendThread->1 MsgStorageAppendResp Term:1 Log:1/12
-2->1 MsgAppResp Term:1 Log:0/12
-3->1 MsgAppResp Term:1 Log:0/12
+2->1 MsgAppResp Term:1 Log:0/12 Commit:11
+3->1 MsgAppResp Term:1 Log:0/12 Commit:11
 AppendThread->2 MsgStorageAppendResp Term:1 Log:1/12
 AppendThread->3 MsgStorageAppendResp Term:1 Log:1/12
 
@@ -373,7 +373,7 @@ process-ready 1 2 3
   1->2 MsgApp Term:1 Log:1/13 Commit:12 Entries:[1/14 EntryNormal "prop_3"]
   1->3 MsgApp Term:1 Log:1/13 Commit:12 Entries:[1/14 EntryNormal "prop_3"]
   1->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:12 Vote:1 Entries:[1/14 EntryNormal "prop_3"] Responses:[
-    1->1 MsgAppResp Term:1 Log:0/14
+    1->1 MsgAppResp Term:1 Log:0/14 Commit:12
     AppendThread->1 MsgStorageAppendResp Term:1 Log:1/14
   ]
   1->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"] Responses:[
@@ -404,8 +404,8 @@ process-ready 1 2 3
   1/12 EntryNormal "prop_1"
   Messages:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:12 Vote:1 Entries:[1/14 EntryNormal "prop_3"] Responses:[
-    2->1 MsgAppResp Term:1 Log:0/13
-    2->1 MsgAppResp Term:1 Log:0/14
+    2->1 MsgAppResp Term:1 Log:0/13 Commit:12
+    2->1 MsgAppResp Term:1 Log:0/14 Commit:12
     AppendThread->2 MsgStorageAppendResp Term:1 Log:1/14
   ]
   2->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"] Responses:[
@@ -420,8 +420,8 @@ process-ready 1 2 3
   1/12 EntryNormal "prop_1"
   Messages:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:12 Vote:1 Entries:[1/14 EntryNormal "prop_3"] Responses:[
-    3->1 MsgAppResp Term:1 Log:0/13
-    3->1 MsgAppResp Term:1 Log:0/14
+    3->1 MsgAppResp Term:1 Log:0/13 Commit:12
+    3->1 MsgAppResp Term:1 Log:0/14 Commit:12
     AppendThread->3 MsgStorageAppendResp Term:1 Log:1/14
   ]
   3->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"] Responses:[
@@ -434,27 +434,27 @@ process-append-thread 1 2 3
   Processing:
   1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"]
   Responses:
-  1->1 MsgAppResp Term:1 Log:0/13
+  1->1 MsgAppResp Term:1 Log:0/13 Commit:11
   AppendThread->1 MsgStorageAppendResp Term:1 Log:1/13
 > 2 processing append thread
   Processing:
   2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"]
   Responses:
-  2->1 MsgAppResp Term:1 Log:0/13
+  2->1 MsgAppResp Term:1 Log:0/13 Commit:11
   AppendThread->2 MsgStorageAppendResp Term:1 Log:1/13
 > 3 processing append thread
   Processing:
   3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"]
   Responses:
-  3->1 MsgAppResp Term:1 Log:0/13
+  3->1 MsgAppResp Term:1 Log:0/13 Commit:11
   AppendThread->3 MsgStorageAppendResp Term:1 Log:1/13
 
 deliver-msgs 1 2 3
 ----
-1->1 MsgAppResp Term:1 Log:0/13
+1->1 MsgAppResp Term:1 Log:0/13 Commit:11
 AppendThread->1 MsgStorageAppendResp Term:1 Log:1/13
-2->1 MsgAppResp Term:1 Log:0/13
-3->1 MsgAppResp Term:1 Log:0/13
+2->1 MsgAppResp Term:1 Log:0/13 Commit:11
+3->1 MsgAppResp Term:1 Log:0/13 Commit:11
 AppendThread->2 MsgStorageAppendResp Term:1 Log:1/13
 AppendThread->3 MsgStorageAppendResp Term:1 Log:1/13
 
@@ -477,7 +477,7 @@ process-ready 1 2 3
   1->2 MsgApp Term:1 Log:1/14 Commit:13 Entries:[1/15 EntryNormal "prop_4"]
   1->3 MsgApp Term:1 Log:1/14 Commit:13 Entries:[1/15 EntryNormal "prop_4"]
   1->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:13 Vote:1 Entries:[1/15 EntryNormal "prop_4"] Responses:[
-    1->1 MsgAppResp Term:1 Log:0/15
+    1->1 MsgAppResp Term:1 Log:0/15 Commit:13
     AppendThread->1 MsgStorageAppendResp Term:1 Log:1/15
   ]
   1->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"] Responses:[
@@ -508,8 +508,8 @@ process-ready 1 2 3
   1/13 EntryNormal "prop_2"
   Messages:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:13 Vote:1 Entries:[1/15 EntryNormal "prop_4"] Responses:[
-    2->1 MsgAppResp Term:1 Log:0/14
-    2->1 MsgAppResp Term:1 Log:0/15
+    2->1 MsgAppResp Term:1 Log:0/14 Commit:13
+    2->1 MsgAppResp Term:1 Log:0/15 Commit:13
     AppendThread->2 MsgStorageAppendResp Term:1 Log:1/15
   ]
   2->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"] Responses:[
@@ -524,8 +524,8 @@ process-ready 1 2 3
   1/13 EntryNormal "prop_2"
   Messages:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:13 Vote:1 Entries:[1/15 EntryNormal "prop_4"] Responses:[
-    3->1 MsgAppResp Term:1 Log:0/14
-    3->1 MsgAppResp Term:1 Log:0/15
+    3->1 MsgAppResp Term:1 Log:0/14 Commit:13
+    3->1 MsgAppResp Term:1 Log:0/15 Commit:13
     AppendThread->3 MsgStorageAppendResp Term:1 Log:1/15
   ]
   3->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"] Responses:[
@@ -538,21 +538,21 @@ process-append-thread 1 2 3
   Processing:
   1->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:12 Vote:1 Entries:[1/14 EntryNormal "prop_3"]
   Responses:
-  1->1 MsgAppResp Term:1 Log:0/14
+  1->1 MsgAppResp Term:1 Log:0/14 Commit:12
   AppendThread->1 MsgStorageAppendResp Term:1 Log:1/14
 > 2 processing append thread
   Processing:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:12 Vote:1 Entries:[1/14 EntryNormal "prop_3"]
   Responses:
-  2->1 MsgAppResp Term:1 Log:0/13
-  2->1 MsgAppResp Term:1 Log:0/14
+  2->1 MsgAppResp Term:1 Log:0/13 Commit:12
+  2->1 MsgAppResp Term:1 Log:0/14 Commit:12
   AppendThread->2 MsgStorageAppendResp Term:1 Log:1/14
 > 3 processing append thread
   Processing:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:12 Vote:1 Entries:[1/14 EntryNormal "prop_3"]
   Responses:
-  3->1 MsgAppResp Term:1 Log:0/13
-  3->1 MsgAppResp Term:1 Log:0/14
+  3->1 MsgAppResp Term:1 Log:0/13 Commit:12
+  3->1 MsgAppResp Term:1 Log:0/14 Commit:12
   AppendThread->3 MsgStorageAppendResp Term:1 Log:1/14
 
 process-apply-thread 1 2 3
@@ -575,12 +575,12 @@ process-apply-thread 1 2 3
 
 deliver-msgs 1 2 3
 ----
-1->1 MsgAppResp Term:1 Log:0/14
+1->1 MsgAppResp Term:1 Log:0/14 Commit:12
 AppendThread->1 MsgStorageAppendResp Term:1 Log:1/14
-2->1 MsgAppResp Term:1 Log:0/13
-2->1 MsgAppResp Term:1 Log:0/14
-3->1 MsgAppResp Term:1 Log:0/13
-3->1 MsgAppResp Term:1 Log:0/14
+2->1 MsgAppResp Term:1 Log:0/13 Commit:12
+2->1 MsgAppResp Term:1 Log:0/14 Commit:12
+3->1 MsgAppResp Term:1 Log:0/13 Commit:12
+3->1 MsgAppResp Term:1 Log:0/14 Commit:12
 ApplyThread->1 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"]
 AppendThread->2 MsgStorageAppendResp Term:1 Log:1/14
 ApplyThread->2 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"]
@@ -624,7 +624,7 @@ process-ready 1 2 3
   1/14 EntryNormal "prop_3"
   Messages:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:14 Vote:1 Responses:[
-    2->1 MsgAppResp Term:1 Log:0/15
+    2->1 MsgAppResp Term:1 Log:0/15 Commit:14
     AppendThread->2 MsgStorageAppendResp Term:1 Log:1/15
   ]
   2->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/14 EntryNormal "prop_3"] Responses:[
@@ -637,7 +637,7 @@ process-ready 1 2 3
   1/14 EntryNormal "prop_3"
   Messages:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:14 Vote:1 Responses:[
-    3->1 MsgAppResp Term:1 Log:0/15
+    3->1 MsgAppResp Term:1 Log:0/15 Commit:14
     AppendThread->3 MsgStorageAppendResp Term:1 Log:1/15
   ]
   3->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/14 EntryNormal "prop_3"] Responses:[
@@ -650,21 +650,21 @@ process-append-thread 1 2 3
   Processing:
   1->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:13 Vote:1 Entries:[1/15 EntryNormal "prop_4"]
   Responses:
-  1->1 MsgAppResp Term:1 Log:0/15
+  1->1 MsgAppResp Term:1 Log:0/15 Commit:13
   AppendThread->1 MsgStorageAppendResp Term:1 Log:1/15
 > 2 processing append thread
   Processing:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:13 Vote:1 Entries:[1/15 EntryNormal "prop_4"]
   Responses:
-  2->1 MsgAppResp Term:1 Log:0/14
-  2->1 MsgAppResp Term:1 Log:0/15
+  2->1 MsgAppResp Term:1 Log:0/14 Commit:13
+  2->1 MsgAppResp Term:1 Log:0/15 Commit:13
   AppendThread->2 MsgStorageAppendResp Term:1 Log:1/15
 > 3 processing append thread
   Processing:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:13 Vote:1 Entries:[1/15 EntryNormal "prop_4"]
   Responses:
-  3->1 MsgAppResp Term:1 Log:0/14
-  3->1 MsgAppResp Term:1 Log:0/15
+  3->1 MsgAppResp Term:1 Log:0/14 Commit:13
+  3->1 MsgAppResp Term:1 Log:0/15 Commit:13
   AppendThread->3 MsgStorageAppendResp Term:1 Log:1/15
 
 process-apply-thread 1 2 3
@@ -687,12 +687,12 @@ process-apply-thread 1 2 3
 
 deliver-msgs 1 2 3
 ----
-1->1 MsgAppResp Term:1 Log:0/15
+1->1 MsgAppResp Term:1 Log:0/15 Commit:13
 AppendThread->1 MsgStorageAppendResp Term:1 Log:1/15
-2->1 MsgAppResp Term:1 Log:0/14
-2->1 MsgAppResp Term:1 Log:0/15
-3->1 MsgAppResp Term:1 Log:0/14
-3->1 MsgAppResp Term:1 Log:0/15
+2->1 MsgAppResp Term:1 Log:0/14 Commit:13
+2->1 MsgAppResp Term:1 Log:0/15 Commit:13
+3->1 MsgAppResp Term:1 Log:0/14 Commit:13
+3->1 MsgAppResp Term:1 Log:0/15 Commit:13
 ApplyThread->1 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"]
 AppendThread->2 MsgStorageAppendResp Term:1 Log:1/15
 ApplyThread->2 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"]
@@ -734,7 +734,7 @@ process-ready 1 2 3
   1/15 EntryNormal "prop_4"
   Messages:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:15 Vote:1 Responses:[
-    2->1 MsgAppResp Term:1 Log:0/15
+    2->1 MsgAppResp Term:1 Log:0/15 Commit:15
   ]
   2->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/15 EntryNormal "prop_4"] Responses:[
     ApplyThread->2 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/15 EntryNormal "prop_4"]
@@ -746,7 +746,7 @@ process-ready 1 2 3
   1/15 EntryNormal "prop_4"
   Messages:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:15 Vote:1 Responses:[
-    3->1 MsgAppResp Term:1 Log:0/15
+    3->1 MsgAppResp Term:1 Log:0/15 Commit:15
   ]
   3->ApplyThread MsgStorageApply Term:0 Log:0/0 Entries:[1/15 EntryNormal "prop_4"] Responses:[
     ApplyThread->3 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/15 EntryNormal "prop_4"]
@@ -758,13 +758,13 @@ process-append-thread 2 3
   Processing:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:14 Vote:1
   Responses:
-  2->1 MsgAppResp Term:1 Log:0/15
+  2->1 MsgAppResp Term:1 Log:0/15 Commit:14
   AppendThread->2 MsgStorageAppendResp Term:1 Log:1/15
 > 3 processing append thread
   Processing:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:14 Vote:1
   Responses:
-  3->1 MsgAppResp Term:1 Log:0/15
+  3->1 MsgAppResp Term:1 Log:0/15 Commit:14
   AppendThread->3 MsgStorageAppendResp Term:1 Log:1/15
 
 process-apply-thread 1 2 3
@@ -787,8 +787,8 @@ process-apply-thread 1 2 3
 
 deliver-msgs 1 2 3
 ----
-2->1 MsgAppResp Term:1 Log:0/15
-3->1 MsgAppResp Term:1 Log:0/15
+2->1 MsgAppResp Term:1 Log:0/15 Commit:14
+3->1 MsgAppResp Term:1 Log:0/15 Commit:14
 ApplyThread->1 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/14 EntryNormal "prop_3"]
 AppendThread->2 MsgStorageAppendResp Term:1 Log:1/15
 INFO entry at index 15 missing from unstable log; ignoring
@@ -812,12 +812,12 @@ process-append-thread 2 3
   Processing:
   2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:15 Vote:1
   Responses:
-  2->1 MsgAppResp Term:1 Log:0/15
+  2->1 MsgAppResp Term:1 Log:0/15 Commit:15
 > 3 processing append thread
   Processing:
   3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:15 Vote:1
   Responses:
-  3->1 MsgAppResp Term:1 Log:0/15
+  3->1 MsgAppResp Term:1 Log:0/15 Commit:15
 
 process-apply-thread 1 2 3
 ----
@@ -839,8 +839,8 @@ process-apply-thread 1 2 3
 
 deliver-msgs 1 2 3
 ----
-2->1 MsgAppResp Term:1 Log:0/15
-3->1 MsgAppResp Term:1 Log:0/15
+2->1 MsgAppResp Term:1 Log:0/15 Commit:15
+3->1 MsgAppResp Term:1 Log:0/15 Commit:15
 ApplyThread->1 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/15 EntryNormal "prop_4"]
 ApplyThread->2 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/15 EntryNormal "prop_4"]
 ApplyThread->3 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/15 EntryNormal "prop_4"]
diff --git a/testdata/async_storage_writes_append_aba_race.txt b/testdata/async_storage_writes_append_aba_race.txt
index 83964fe7..f2cbfb02 100644
--- a/testdata/async_storage_writes_append_aba_race.txt
+++ b/testdata/async_storage_writes_append_aba_race.txt
@@ -43,7 +43,7 @@ Messages:
 2->6 MsgApp Term:1 Log:1/11 Commit:11 Entries:[1/12 EntryNormal "init_prop"]
 2->7 MsgApp Term:1 Log:1/11 Commit:11 Entries:[1/12 EntryNormal "init_prop"]
 2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "init_prop"] Responses:[
-  2->2 MsgAppResp Term:1 Log:0/12
+  2->2 MsgAppResp Term:1 Log:0/12 Commit:11
   AppendThread->2 MsgStorageAppendResp Term:1 Log:1/12
 ]
 
@@ -65,7 +65,7 @@ Entries:
 1/12 EntryNormal "init_prop"
 Messages:
 1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "init_prop"] Responses:[
-  1->2 MsgAppResp Term:1 Log:0/12
+  1->2 MsgAppResp Term:1 Log:0/12 Commit:11
   AppendThread->1 MsgStorageAppendResp Term:1 Log:1/12
 ]
 
@@ -198,7 +198,7 @@ Messages:
 3->6 MsgApp Term:2 Log:1/11 Commit:11 Entries:[2/12 EntryNormal ""]
 3->7 MsgApp Term:2 Log:1/11 Commit:11 Entries:[2/12 EntryNormal ""]
 3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[2/12 EntryNormal ""] Responses:[
-  3->3 MsgAppResp Term:2 Log:0/12
+  3->3 MsgAppResp Term:2 Log:0/12 Commit:11
   AppendThread->3 MsgStorageAppendResp Term:2 Log:2/12
 ]
 
@@ -229,7 +229,7 @@ Entries:
 Messages:
 1->AppendThread MsgStorageAppend Term:2 Log:0/0 Commit:11 Entries:[2/12 EntryNormal ""] Responses:[
   1->3 MsgVoteResp Term:2 Log:0/0 Rejected (Hint: 0)
-  1->3 MsgAppResp Term:2 Log:0/12
+  1->3 MsgAppResp Term:2 Log:0/12 Commit:11
   AppendThread->1 MsgStorageAppendResp Term:2 Log:2/12
 ]
 
@@ -355,7 +355,7 @@ Messages:
 4->6 MsgApp Term:3 Log:1/11 Commit:11 Entries:[3/12 EntryNormal ""]
 4->7 MsgApp Term:3 Log:1/11 Commit:11 Entries:[3/12 EntryNormal ""]
 4->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[3/12 EntryNormal ""] Responses:[
-  4->4 MsgAppResp Term:3 Log:0/12
+  4->4 MsgAppResp Term:3 Log:0/12 Commit:11
   AppendThread->4 MsgStorageAppendResp Term:3 Log:3/12
 ]
 
@@ -425,7 +425,7 @@ Entries:
 3/12 EntryNormal ""
 Messages:
 1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[3/12 EntryNormal ""] Responses:[
-  1->4 MsgAppResp Term:3 Log:0/12
+  1->4 MsgAppResp Term:3 Log:0/12 Commit:11
   AppendThread->1 MsgStorageAppendResp Term:3 Log:3/12
 ]
 
@@ -442,7 +442,7 @@ process-append-thread 1
 Processing:
 1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "init_prop"]
 Responses:
-1->2 MsgAppResp Term:1 Log:0/12
+1->2 MsgAppResp Term:1 Log:0/12 Commit:11
 AppendThread->1 MsgStorageAppendResp Term:1 Log:1/12
 
 raft-log 1
@@ -469,7 +469,7 @@ Processing:
 1->AppendThread MsgStorageAppend Term:2 Log:0/0 Commit:11 Entries:[2/12 EntryNormal ""]
 Responses:
 1->3 MsgVoteResp Term:2 Log:0/0 Rejected (Hint: 0)
-1->3 MsgAppResp Term:2 Log:0/12
+1->3 MsgAppResp Term:2 Log:0/12 Commit:11
 AppendThread->1 MsgStorageAppendResp Term:2 Log:2/12
 
 raft-log 1
@@ -504,7 +504,7 @@ process-append-thread 1
 Processing:
 1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[3/12 EntryNormal ""]
 Responses:
-1->4 MsgAppResp Term:3 Log:0/12
+1->4 MsgAppResp Term:3 Log:0/12 Commit:11
 AppendThread->1 MsgStorageAppendResp Term:3 Log:3/12
 
 raft-log 1
diff --git a/testdata/campaign.txt b/testdata/campaign.txt
index 4eefab36..3538aa64 100644
--- a/testdata/campaign.txt
+++ b/testdata/campaign.txt
@@ -76,17 +76,17 @@ stabilize
   Entries:
   1/3 EntryNormal ""
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/3
+  2->1 MsgAppResp Term:1 Log:0/3 Commit:2
 > 3 handling Ready
   Ready MustSync=true:
   Lead:1 State:StateFollower
   Entries:
   1/3 EntryNormal ""
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/3
+  3->1 MsgAppResp Term:1 Log:0/3 Commit:2
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/3
-  3->1 MsgAppResp Term:1 Log:0/3
+  2->1 MsgAppResp Term:1 Log:0/3 Commit:2
+  3->1 MsgAppResp Term:1 Log:0/3 Commit:2
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:3
@@ -105,14 +105,14 @@ stabilize
   CommittedEntries:
   1/3 EntryNormal ""
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/3
+  2->1 MsgAppResp Term:1 Log:0/3 Commit:3
 > 3 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:3
   CommittedEntries:
   1/3 EntryNormal ""
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/3
+  3->1 MsgAppResp Term:1 Log:0/3 Commit:3
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/3
-  3->1 MsgAppResp Term:1 Log:0/3
+  2->1 MsgAppResp Term:1 Log:0/3 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/3 Commit:3
diff --git a/testdata/campaign_learner_must_vote.txt b/testdata/campaign_learner_must_vote.txt
index d05de374..9da576ff 100644
--- a/testdata/campaign_learner_must_vote.txt
+++ b/testdata/campaign_learner_must_vote.txt
@@ -135,10 +135,10 @@ stabilize 2 3
   CommittedEntries:
   1/4 EntryConfChangeV2 v3
   Messages:
-  3->2 MsgAppResp Term:2 Log:0/5
+  3->2 MsgAppResp Term:2 Log:0/5 Commit:4
   INFO 3 switched to configuration voters=(1 2 3)
 > 2 receiving messages
-  3->2 MsgAppResp Term:2 Log:0/5
+  3->2 MsgAppResp Term:2 Log:0/5 Commit:4
 > 2 handling Ready
   Ready MustSync=false:
   HardState Term:2 Vote:2 Commit:5
@@ -154,6 +154,6 @@ stabilize 2 3
   CommittedEntries:
   2/5 EntryNormal ""
   Messages:
-  3->2 MsgAppResp Term:2 Log:0/5
+  3->2 MsgAppResp Term:2 Log:0/5 Commit:5
 > 2 receiving messages
-  3->2 MsgAppResp Term:2 Log:0/5
+  3->2 MsgAppResp Term:2 Log:0/5 Commit:5
diff --git a/testdata/checkquorum.txt b/testdata/checkquorum.txt
index b25c1e63..065e0754 100644
--- a/testdata/checkquorum.txt
+++ b/testdata/checkquorum.txt
@@ -193,7 +193,7 @@ stabilize
   Entries:
   3/12 EntryNormal ""
   Messages:
-  1->2 MsgAppResp Term:3 Log:0/12
+  1->2 MsgAppResp Term:3 Log:0/12 Commit:11
 > 3 handling Ready
   Ready MustSync=true:
   Lead:2 State:StateFollower
@@ -201,10 +201,10 @@ stabilize
   Entries:
   3/12 EntryNormal ""
   Messages:
-  3->2 MsgAppResp Term:3 Log:0/12
+  3->2 MsgAppResp Term:3 Log:0/12 Commit:11
 > 2 receiving messages
-  1->2 MsgAppResp Term:3 Log:0/12
-  3->2 MsgAppResp Term:3 Log:0/12
+  1->2 MsgAppResp Term:3 Log:0/12 Commit:11
+  3->2 MsgAppResp Term:3 Log:0/12 Commit:11
 > 2 handling Ready
   Ready MustSync=false:
   HardState Term:3 Vote:2 Commit:12
@@ -223,14 +223,14 @@ stabilize
   CommittedEntries:
   3/12 EntryNormal ""
   Messages:
-  1->2 MsgAppResp Term:3 Log:0/12
+  1->2 MsgAppResp Term:3 Log:0/12 Commit:12
 > 3 handling Ready
   Ready MustSync=false:
   HardState Term:3 Commit:12
   CommittedEntries:
   3/12 EntryNormal ""
   Messages:
-  3->2 MsgAppResp Term:3 Log:0/12
+  3->2 MsgAppResp Term:3 Log:0/12 Commit:12
 > 2 receiving messages
-  1->2 MsgAppResp Term:3 Log:0/12
-  3->2 MsgAppResp Term:3 Log:0/12
+  1->2 MsgAppResp Term:3 Log:0/12 Commit:12
+  3->2 MsgAppResp Term:3 Log:0/12 Commit:12
diff --git a/testdata/confchange_v1_remove_leader.txt b/testdata/confchange_v1_remove_leader.txt
index cc91508a..fde99c82 100644
--- a/testdata/confchange_v1_remove_leader.txt
+++ b/testdata/confchange_v1_remove_leader.txt
@@ -70,8 +70,8 @@ stabilize 2
   1/4 EntryConfChange r1
   1/5 EntryNormal "foo"
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/4
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:3
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:3
 
 # Put another entry in n1's log.
 propose 1 bar
@@ -92,8 +92,8 @@ stabilize 1
   1->2 MsgApp Term:1 Log:1/5 Commit:3 Entries:[1/6 EntryNormal "bar"]
   1->3 MsgApp Term:1 Log:1/5 Commit:3 Entries:[1/6 EntryNormal "bar"]
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/4
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:3
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:3
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:5
@@ -129,18 +129,18 @@ stabilize 2
   1/4 EntryConfChange r1
   1/5 EntryNormal "foo"
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:3
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:4
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:5
   INFO 2 switched to configuration voters=(2 3)
 
 # ... which thankfully is what we see on the leader.
 stabilize 1
 ----
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:3
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:4
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:5
 
 # When n3 responds, quorum is reached and everything falls into place.
 stabilize
@@ -162,18 +162,18 @@ stabilize
   1/4 EntryConfChange r1
   1/5 EntryNormal "foo"
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/4
-  3->1 MsgAppResp Term:1 Log:0/5
-  3->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
+  3->1 MsgAppResp Term:1 Log:0/4 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:4
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:5
   INFO 3 switched to configuration voters=(2 3)
 > 1 receiving messages
-  3->1 MsgAppResp Term:1 Log:0/4
-  3->1 MsgAppResp Term:1 Log:0/5
-  3->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
+  3->1 MsgAppResp Term:1 Log:0/4 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:4
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:5
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:6
@@ -192,17 +192,17 @@ stabilize
   CommittedEntries:
   1/6 EntryNormal "bar"
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:6
 > 3 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:6
   CommittedEntries:
   1/6 EntryNormal "bar"
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/6
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:6
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:6
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:6
 
 # However not all is well. n1 is still leader but unconditionally drops all
 # proposals on the floor, so we're effectively stuck if it still heartbeats
diff --git a/testdata/confchange_v1_remove_leader_stepdown.txt b/testdata/confchange_v1_remove_leader_stepdown.txt
index fe397650..b9e14ff0 100644
--- a/testdata/confchange_v1_remove_leader_stepdown.txt
+++ b/testdata/confchange_v1_remove_leader_stepdown.txt
@@ -71,8 +71,8 @@ stabilize 2
   1/4 EntryConfChange r1
   1/5 EntryNormal "foo"
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/4
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:3
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:3
 
 # Put another entry in n1's log.
 propose 1 bar
@@ -91,8 +91,8 @@ stabilize 1
   1->2 MsgApp Term:1 Log:1/5 Commit:3 Entries:[1/6 EntryNormal "bar"]
   1->3 MsgApp Term:1 Log:1/5 Commit:3 Entries:[1/6 EntryNormal "bar"]
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/4
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:3
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:3
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:5
@@ -132,18 +132,18 @@ stabilize 2
   1/4 EntryConfChange r1
   1/5 EntryNormal "foo"
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:3
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:4
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:5
   INFO 2 switched to configuration voters=(2 3)
 
 # ...because the old leader n1 ignores the append responses.
 stabilize 1
 ----
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:3
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:4
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:5
 
 # When n3 responds, quorum is reached and everything falls into place.
 stabilize
@@ -165,18 +165,18 @@ stabilize
   1/4 EntryConfChange r1
   1/5 EntryNormal "foo"
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/4
-  3->1 MsgAppResp Term:1 Log:0/5
-  3->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
+  3->1 MsgAppResp Term:1 Log:0/4 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:4
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:5
   INFO 3 switched to configuration voters=(2 3)
 > 1 receiving messages
-  3->1 MsgAppResp Term:1 Log:0/4
-  3->1 MsgAppResp Term:1 Log:0/5
-  3->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
+  3->1 MsgAppResp Term:1 Log:0/4 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:4
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:5
 
 # n1 can no longer propose.
 propose 1 baz
diff --git a/testdata/confchange_v2_add_double_auto.txt b/testdata/confchange_v2_add_double_auto.txt
index f290c980..0d86ac1a 100644
--- a/testdata/confchange_v2_add_double_auto.txt
+++ b/testdata/confchange_v2_add_double_auto.txt
@@ -128,9 +128,9 @@ stabilize 1 2
   Entries:
   1/5 EntryConfChangeV2
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:4
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:4
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:5
@@ -147,10 +147,10 @@ stabilize 1 2
   CommittedEntries:
   1/5 EntryConfChangeV2
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:5
   INFO 2 switched to configuration voters=(1 2 3)
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:5
 
 # n3 immediately receives a snapshot in the final configuration.
 stabilize 1 3
@@ -230,13 +230,13 @@ stabilize 2 3
   Entries:
   1/6 EntryConfChangeV2 r2 r3
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:5
 > 3 handling Ready
   Ready MustSync=true:
   Entries:
   1/6 EntryConfChangeV2 r2 r3
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/6
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:5
 
 # n1 gets some more proposals. This is part of a regression test: There used to
 # be a bug in which these proposals would prompt the leader to transition out of
@@ -264,8 +264,8 @@ stabilize 1
   1->2 MsgApp Term:1 Log:1/7 Commit:5 Entries:[1/8 EntryNormal "bar"]
   1->3 MsgApp Term:1 Log:1/7 Commit:5 Entries:[1/8 EntryNormal "bar"]
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/6
-  3->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:5
+  3->1 MsgAppResp Term:1 Log:0/6 Commit:5
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:6
@@ -307,10 +307,10 @@ stabilize 2 3
   CommittedEntries:
   1/6 EntryConfChangeV2 r2 r3
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/7
-  2->1 MsgAppResp Term:1 Log:0/8
-  2->1 MsgAppResp Term:1 Log:0/8
-  2->1 MsgAppResp Term:1 Log:0/9
+  2->1 MsgAppResp Term:1 Log:0/7 Commit:5
+  2->1 MsgAppResp Term:1 Log:0/8 Commit:5
+  2->1 MsgAppResp Term:1 Log:0/8 Commit:6
+  2->1 MsgAppResp Term:1 Log:0/9 Commit:6
   INFO 2 switched to configuration voters=(1)&&(1 2 3) autoleave
 > 3 handling Ready
   Ready MustSync=true:
@@ -322,10 +322,10 @@ stabilize 2 3
   CommittedEntries:
   1/6 EntryConfChangeV2 r2 r3
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/7
-  3->1 MsgAppResp Term:1 Log:0/8
-  3->1 MsgAppResp Term:1 Log:0/8
-  3->1 MsgAppResp Term:1 Log:0/9
+  3->1 MsgAppResp Term:1 Log:0/7 Commit:5
+  3->1 MsgAppResp Term:1 Log:0/8 Commit:5
+  3->1 MsgAppResp Term:1 Log:0/8 Commit:6
+  3->1 MsgAppResp Term:1 Log:0/9 Commit:6
   INFO 3 switched to configuration voters=(1)&&(1 2 3) autoleave
 
 # n2 and n3 also leave the joint config and the dust settles. We see at the very
@@ -334,14 +334,14 @@ stabilize 2 3
 stabilize
 ----
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/7
-  2->1 MsgAppResp Term:1 Log:0/8
-  2->1 MsgAppResp Term:1 Log:0/8
-  2->1 MsgAppResp Term:1 Log:0/9
-  3->1 MsgAppResp Term:1 Log:0/7
-  3->1 MsgAppResp Term:1 Log:0/8
-  3->1 MsgAppResp Term:1 Log:0/8
-  3->1 MsgAppResp Term:1 Log:0/9
+  2->1 MsgAppResp Term:1 Log:0/7 Commit:5
+  2->1 MsgAppResp Term:1 Log:0/8 Commit:5
+  2->1 MsgAppResp Term:1 Log:0/8 Commit:6
+  2->1 MsgAppResp Term:1 Log:0/9 Commit:6
+  3->1 MsgAppResp Term:1 Log:0/7 Commit:5
+  3->1 MsgAppResp Term:1 Log:0/8 Commit:5
+  3->1 MsgAppResp Term:1 Log:0/8 Commit:6
+  3->1 MsgAppResp Term:1 Log:0/9 Commit:6
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:9
@@ -373,9 +373,9 @@ stabilize
   1/8 EntryNormal "bar"
   1/9 EntryConfChangeV2
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/9
-  2->1 MsgAppResp Term:1 Log:0/9
-  2->1 MsgAppResp Term:1 Log:0/9
+  2->1 MsgAppResp Term:1 Log:0/9 Commit:7
+  2->1 MsgAppResp Term:1 Log:0/9 Commit:8
+  2->1 MsgAppResp Term:1 Log:0/9 Commit:9
   INFO 2 switched to configuration voters=(1)
 > 3 handling Ready
   Ready MustSync=false:
@@ -385,20 +385,20 @@ stabilize
   1/8 EntryNormal "bar"
   1/9 EntryConfChangeV2
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/9
-  3->1 MsgAppResp Term:1 Log:0/9
-  3->1 MsgAppResp Term:1 Log:0/9
+  3->1 MsgAppResp Term:1 Log:0/9 Commit:7
+  3->1 MsgAppResp Term:1 Log:0/9 Commit:8
+  3->1 MsgAppResp Term:1 Log:0/9 Commit:9
   INFO 3 switched to configuration voters=(1)
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/9
+  2->1 MsgAppResp Term:1 Log:0/9 Commit:7
   raft: cannot step as peer not found
-  2->1 MsgAppResp Term:1 Log:0/9
+  2->1 MsgAppResp Term:1 Log:0/9 Commit:8
   raft: cannot step as peer not found
-  2->1 MsgAppResp Term:1 Log:0/9
+  2->1 MsgAppResp Term:1 Log:0/9 Commit:9
   raft: cannot step as peer not found
-  3->1 MsgAppResp Term:1 Log:0/9
+  3->1 MsgAppResp Term:1 Log:0/9 Commit:7
   raft: cannot step as peer not found
-  3->1 MsgAppResp Term:1 Log:0/9
+  3->1 MsgAppResp Term:1 Log:0/9 Commit:8
   raft: cannot step as peer not found
-  3->1 MsgAppResp Term:1 Log:0/9
+  3->1 MsgAppResp Term:1 Log:0/9 Commit:9
   raft: cannot step as peer not found
diff --git a/testdata/confchange_v2_add_double_implicit.txt b/testdata/confchange_v2_add_double_implicit.txt
index 2db3b7c1..30f26f68 100644
--- a/testdata/confchange_v2_add_double_implicit.txt
+++ b/testdata/confchange_v2_add_double_implicit.txt
@@ -111,9 +111,9 @@ stabilize 1 2
   Entries:
   1/5 EntryConfChangeV2
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:4
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:4
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:5
@@ -130,7 +130,7 @@ stabilize 1 2
   CommittedEntries:
   1/5 EntryConfChangeV2
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:5
   INFO 2 switched to configuration voters=(1 2)
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:5
diff --git a/testdata/confchange_v2_add_single_explicit.txt b/testdata/confchange_v2_add_single_explicit.txt
index 1d390e55..770c9a27 100644
--- a/testdata/confchange_v2_add_single_explicit.txt
+++ b/testdata/confchange_v2_add_single_explicit.txt
@@ -129,11 +129,11 @@ stabilize
   1/5 EntryNormal ""
   1/6 EntryConfChangeV2
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/5
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:4
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:4
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/5
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:4
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:4
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:6
@@ -154,12 +154,12 @@ stabilize
   1/5 EntryNormal ""
   1/6 EntryConfChangeV2
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:5
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:6
   INFO 2 switched to configuration voters=(1 2)
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/6
-  2->1 MsgAppResp Term:1 Log:0/6
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:5
+  2->1 MsgAppResp Term:1 Log:0/6 Commit:6
 
 # Check that trying to transition out again won't do anything.
 propose-conf-change 1
@@ -182,9 +182,9 @@ stabilize
   Entries:
   1/7 EntryNormal ""
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/7
+  2->1 MsgAppResp Term:1 Log:0/7 Commit:6
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/7
+  2->1 MsgAppResp Term:1 Log:0/7 Commit:6
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:7
@@ -200,6 +200,6 @@ stabilize
   CommittedEntries:
   1/7 EntryNormal ""
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/7
+  2->1 MsgAppResp Term:1 Log:0/7 Commit:7
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/7
+  2->1 MsgAppResp Term:1 Log:0/7 Commit:7
diff --git a/testdata/confchange_v2_replace_leader.txt b/testdata/confchange_v2_replace_leader.txt
index 628cc447..a2b8425c 100644
--- a/testdata/confchange_v2_replace_leader.txt
+++ b/testdata/confchange_v2_replace_leader.txt
@@ -65,16 +65,16 @@ stabilize
   Entries:
   1/4 EntryConfChangeV2 r1 v4
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:3
 > 3 handling Ready
   Ready MustSync=true:
   Entries:
   1/4 EntryConfChangeV2 r1 v4
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/4
+  3->1 MsgAppResp Term:1 Log:0/4 Commit:3
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/4
-  3->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:3
+  3->1 MsgAppResp Term:1 Log:0/4 Commit:3
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:4
@@ -98,7 +98,7 @@ stabilize
   CommittedEntries:
   1/4 EntryConfChangeV2 r1 v4
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:4
   INFO 2 switched to configuration voters=(2 3 4)&&(1 2 3)
 > 3 handling Ready
   Ready MustSync=false:
@@ -106,11 +106,11 @@ stabilize
   CommittedEntries:
   1/4 EntryConfChangeV2 r1 v4
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/4
+  3->1 MsgAppResp Term:1 Log:0/4 Commit:4
   INFO 3 switched to configuration voters=(2 3 4)&&(1 2 3)
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/4
-  3->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:4
+  3->1 MsgAppResp Term:1 Log:0/4 Commit:4
 > 4 receiving messages
   1->4 MsgApp Term:1 Log:1/3 Commit:4 Entries:[1/4 EntryConfChangeV2 r1 v4]
   INFO 4 [term: 0] received a MsgApp message with higher term from 1 [term: 1]
@@ -247,25 +247,25 @@ stabilize
   Entries:
   2/5 EntryNormal ""
   Messages:
-  1->4 MsgAppResp Term:2 Log:0/5
+  1->4 MsgAppResp Term:2 Log:0/5 Commit:4
 > 2 handling Ready
   Ready MustSync=true:
   Lead:4 State:StateFollower
   Entries:
   2/5 EntryNormal ""
   Messages:
-  2->4 MsgAppResp Term:2 Log:0/5
+  2->4 MsgAppResp Term:2 Log:0/5 Commit:4
 > 3 handling Ready
   Ready MustSync=true:
   Lead:4 State:StateFollower
   Entries:
   2/5 EntryNormal ""
   Messages:
-  3->4 MsgAppResp Term:2 Log:0/5
+  3->4 MsgAppResp Term:2 Log:0/5 Commit:4
 > 4 receiving messages
-  1->4 MsgAppResp Term:2 Log:0/5
-  2->4 MsgAppResp Term:2 Log:0/5
-  3->4 MsgAppResp Term:2 Log:0/5
+  1->4 MsgAppResp Term:2 Log:0/5 Commit:4
+  2->4 MsgAppResp Term:2 Log:0/5 Commit:4
+  3->4 MsgAppResp Term:2 Log:0/5 Commit:4
 > 4 handling Ready
   Ready MustSync=false:
   HardState Term:2 Vote:4 Commit:5
@@ -287,25 +287,25 @@ stabilize
   CommittedEntries:
   2/5 EntryNormal ""
   Messages:
-  1->4 MsgAppResp Term:2 Log:0/5
+  1->4 MsgAppResp Term:2 Log:0/5 Commit:5
 > 2 handling Ready
   Ready MustSync=false:
   HardState Term:2 Vote:4 Commit:5
   CommittedEntries:
   2/5 EntryNormal ""
   Messages:
-  2->4 MsgAppResp Term:2 Log:0/5
+  2->4 MsgAppResp Term:2 Log:0/5 Commit:5
 > 3 handling Ready
   Ready MustSync=false:
   HardState Term:2 Vote:4 Commit:5
   CommittedEntries:
   2/5 EntryNormal ""
   Messages:
-  3->4 MsgAppResp Term:2 Log:0/5
+  3->4 MsgAppResp Term:2 Log:0/5 Commit:5
 > 4 receiving messages
-  1->4 MsgAppResp Term:2 Log:0/5
-  2->4 MsgAppResp Term:2 Log:0/5
-  3->4 MsgAppResp Term:2 Log:0/5
+  1->4 MsgAppResp Term:2 Log:0/5 Commit:5
+  2->4 MsgAppResp Term:2 Log:0/5 Commit:5
+  3->4 MsgAppResp Term:2 Log:0/5 Commit:5
 
 # Leadership transfer succeeded.
 raft-state
@@ -342,23 +342,23 @@ stabilize
   Entries:
   2/6 EntryConfChangeV2
   Messages:
-  1->4 MsgAppResp Term:2 Log:0/6
+  1->4 MsgAppResp Term:2 Log:0/6 Commit:5
 > 2 handling Ready
   Ready MustSync=true:
   Entries:
   2/6 EntryConfChangeV2
   Messages:
-  2->4 MsgAppResp Term:2 Log:0/6
+  2->4 MsgAppResp Term:2 Log:0/6 Commit:5
 > 3 handling Ready
   Ready MustSync=true:
   Entries:
   2/6 EntryConfChangeV2
   Messages:
-  3->4 MsgAppResp Term:2 Log:0/6
+  3->4 MsgAppResp Term:2 Log:0/6 Commit:5
 > 4 receiving messages
-  1->4 MsgAppResp Term:2 Log:0/6
-  2->4 MsgAppResp Term:2 Log:0/6
-  3->4 MsgAppResp Term:2 Log:0/6
+  1->4 MsgAppResp Term:2 Log:0/6 Commit:5
+  2->4 MsgAppResp Term:2 Log:0/6 Commit:5
+  3->4 MsgAppResp Term:2 Log:0/6 Commit:5
 > 4 handling Ready
   Ready MustSync=false:
   HardState Term:2 Vote:4 Commit:6
@@ -381,7 +381,7 @@ stabilize
   CommittedEntries:
   2/6 EntryConfChangeV2
   Messages:
-  1->4 MsgAppResp Term:2 Log:0/6
+  1->4 MsgAppResp Term:2 Log:0/6 Commit:6
   INFO 1 switched to configuration voters=(2 3 4)
 > 2 handling Ready
   Ready MustSync=false:
@@ -389,7 +389,7 @@ stabilize
   CommittedEntries:
   2/6 EntryConfChangeV2
   Messages:
-  2->4 MsgAppResp Term:2 Log:0/6
+  2->4 MsgAppResp Term:2 Log:0/6 Commit:6
   INFO 2 switched to configuration voters=(2 3 4)
 > 3 handling Ready
   Ready MustSync=false:
@@ -397,13 +397,13 @@ stabilize
   CommittedEntries:
   2/6 EntryConfChangeV2
   Messages:
-  3->4 MsgAppResp Term:2 Log:0/6
+  3->4 MsgAppResp Term:2 Log:0/6 Commit:6
   INFO 3 switched to configuration voters=(2 3 4)
 > 4 receiving messages
-  1->4 MsgAppResp Term:2 Log:0/6
+  1->4 MsgAppResp Term:2 Log:0/6 Commit:6
   raft: cannot step as peer not found
-  2->4 MsgAppResp Term:2 Log:0/6
-  3->4 MsgAppResp Term:2 Log:0/6
+  2->4 MsgAppResp Term:2 Log:0/6 Commit:6
+  3->4 MsgAppResp Term:2 Log:0/6 Commit:6
 
 # n1 is out of the configuration.
 raft-state
diff --git a/testdata/confchange_v2_replace_leader_stepdown.txt b/testdata/confchange_v2_replace_leader_stepdown.txt
index 62d01d23..ecad1d7c 100644
--- a/testdata/confchange_v2_replace_leader_stepdown.txt
+++ b/testdata/confchange_v2_replace_leader_stepdown.txt
@@ -93,23 +93,23 @@ stabilize
   Entries:
   1/5 EntryConfChangeV2
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:4
 > 3 handling Ready
   Ready MustSync=true:
   Entries:
   1/5 EntryConfChangeV2
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/5
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:4
 > 4 handling Ready
   Ready MustSync=true:
   Entries:
   1/5 EntryConfChangeV2
   Messages:
-  4->1 MsgAppResp Term:1 Log:0/5
+  4->1 MsgAppResp Term:1 Log:0/5 Commit:4
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/5
-  3->1 MsgAppResp Term:1 Log:0/5
-  4->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:4
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:4
+  4->1 MsgAppResp Term:1 Log:0/5 Commit:4
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:5
@@ -136,7 +136,7 @@ stabilize
   CommittedEntries:
   1/5 EntryConfChangeV2
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:5
   INFO 2 switched to configuration voters=(2 3 4)
 > 3 handling Ready
   Ready MustSync=false:
@@ -144,7 +144,7 @@ stabilize
   CommittedEntries:
   1/5 EntryConfChangeV2
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/5
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:5
   INFO 3 switched to configuration voters=(2 3 4)
 > 4 handling Ready
   Ready MustSync=false:
@@ -152,12 +152,12 @@ stabilize
   CommittedEntries:
   1/5 EntryConfChangeV2
   Messages:
-  4->1 MsgAppResp Term:1 Log:0/5
+  4->1 MsgAppResp Term:1 Log:0/5 Commit:5
   INFO 4 switched to configuration voters=(2 3 4)
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/5
-  3->1 MsgAppResp Term:1 Log:0/5
-  4->1 MsgAppResp Term:1 Log:0/5
+  2->1 MsgAppResp Term:1 Log:0/5 Commit:5
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:5
+  4->1 MsgAppResp Term:1 Log:0/5 Commit:5
 
 # n1 is out of the configuration.
 raft-state
diff --git a/testdata/forget_leader_prevote_checkquorum.txt b/testdata/forget_leader_prevote_checkquorum.txt
index 9b3b80ff..d204b9d7 100644
--- a/testdata/forget_leader_prevote_checkquorum.txt
+++ b/testdata/forget_leader_prevote_checkquorum.txt
@@ -182,7 +182,7 @@ stabilize 2
   Entries:
   2/13 EntryNormal "prop_1"
   Messages:
-  2->3 MsgAppResp Term:2 Log:0/13
+  2->3 MsgAppResp Term:2 Log:0/13 Commit:12
 
 forget-leader 2
 ----
diff --git a/testdata/heartbeat_resp_recovers_from_probing.txt b/testdata/heartbeat_resp_recovers_from_probing.txt
index e606a155..bb6eef1e 100644
--- a/testdata/heartbeat_resp_recovers_from_probing.txt
+++ b/testdata/heartbeat_resp_recovers_from_probing.txt
@@ -79,9 +79,9 @@ stabilize
 > 2 handling Ready
   Ready MustSync=false:
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/11
+  2->1 MsgAppResp Term:1 Log:0/11 Commit:11
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/11
+  2->1 MsgAppResp Term:1 Log:0/11 Commit:11
 
 status 1
 ----
diff --git a/testdata/lagging_commit.txt b/testdata/lagging_commit.txt
index 8f8ba336..551d4e75 100644
--- a/testdata/lagging_commit.txt
+++ b/testdata/lagging_commit.txt
@@ -51,15 +51,15 @@ Entries:
 1/12 EntryNormal "data1"
 1/13 EntryNormal "data2"
 Messages:
-3->1 MsgAppResp Term:1 Log:0/12
-3->1 MsgAppResp Term:1 Log:0/13
+3->1 MsgAppResp Term:1 Log:0/12 Commit:11
+3->1 MsgAppResp Term:1 Log:0/13 Commit:11
 
 # Suppose there is a network blip which prevents the leader learning that the
 # follower 3 has appended the proposed entries to the log.
 deliver-msgs drop=(1)
 ----
-dropped: 3->1 MsgAppResp Term:1 Log:0/12
-dropped: 3->1 MsgAppResp Term:1 Log:0/13
+dropped: 3->1 MsgAppResp Term:1 Log:0/12 Commit:11
+dropped: 3->1 MsgAppResp Term:1 Log:0/13 Commit:11
 
 # In the meantime, the entries are committed, and the leader sends the commit
 # index to all the followers.
@@ -71,11 +71,11 @@ stabilize 1 2
   1/12 EntryNormal "data1"
   1/13 EntryNormal "data2"
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/12
-  2->1 MsgAppResp Term:1 Log:0/13
+  2->1 MsgAppResp Term:1 Log:0/12 Commit:11
+  2->1 MsgAppResp Term:1 Log:0/13 Commit:11
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/12
-  2->1 MsgAppResp Term:1 Log:0/13
+  2->1 MsgAppResp Term:1 Log:0/12 Commit:11
+  2->1 MsgAppResp Term:1 Log:0/13 Commit:11
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:1 Vote:1 Commit:13
@@ -97,11 +97,11 @@ stabilize 1 2
   1/12 EntryNormal "data1"
   1/13 EntryNormal "data2"
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/13
-  2->1 MsgAppResp Term:1 Log:0/13
+  2->1 MsgAppResp Term:1 Log:0/13 Commit:12
+  2->1 MsgAppResp Term:1 Log:0/13 Commit:13
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/13
-  2->1 MsgAppResp Term:1 Log:0/13
+  2->1 MsgAppResp Term:1 Log:0/13 Commit:12
+  2->1 MsgAppResp Term:1 Log:0/13 Commit:13
 
 # The network blip prevents the follower 3 from learning that the previously
 # appended entries are now committed.
@@ -169,6 +169,6 @@ stabilize 1 3
   1/12 EntryNormal "data1"
   1/13 EntryNormal "data2"
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/13
+  3->1 MsgAppResp Term:1 Log:0/13 Commit:13
 > 1 receiving messages
-  3->1 MsgAppResp Term:1 Log:0/13
+  3->1 MsgAppResp Term:1 Log:0/13 Commit:13
diff --git a/testdata/prevote.txt b/testdata/prevote.txt
index db763d35..f4926d43 100644
--- a/testdata/prevote.txt
+++ b/testdata/prevote.txt
@@ -49,7 +49,7 @@ Ready MustSync=true:
 Entries:
 1/12 EntryNormal "prop_1"
 Messages:
-2->1 MsgAppResp Term:1 Log:0/12
+2->1 MsgAppResp Term:1 Log:0/12 Commit:11
 
 # 3 is now behind on its log. Attempt to campaign.
 raft-log 3
@@ -75,7 +75,7 @@ INFO 3 has received 1 MsgPreVoteResp votes and 0 vote rejections
 
 deliver-msgs 1 2
 ----
-2->1 MsgAppResp Term:1 Log:0/12
+2->1 MsgAppResp Term:1 Log:0/12 Commit:11
 3->1 MsgPreVote Term:2 Log:1/11
 INFO 1 [logterm: 1, index: 12, vote: 1] rejected MsgPreVote from 3 [logterm: 1, index: 11] at term 1
 3->2 MsgPreVote Term:2 Log:1/11
@@ -111,7 +111,7 @@ stabilize
   CommittedEntries:
   1/12 EntryNormal "prop_1"
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/12
+  2->1 MsgAppResp Term:1 Log:0/12 Commit:12
 > 3 handling Ready
   Ready MustSync=true:
   Lead:1 State:StateFollower
@@ -121,12 +121,12 @@ stabilize
   CommittedEntries:
   1/12 EntryNormal "prop_1"
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/12
-  3->1 MsgAppResp Term:1 Log:0/12
+  3->1 MsgAppResp Term:1 Log:0/12 Commit:11
+  3->1 MsgAppResp Term:1 Log:0/12 Commit:12
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/12
-  3->1 MsgAppResp Term:1 Log:0/12
-  3->1 MsgAppResp Term:1 Log:0/12
+  2->1 MsgAppResp Term:1 Log:0/12 Commit:12
+  3->1 MsgAppResp Term:1 Log:0/12 Commit:11
+  3->1 MsgAppResp Term:1 Log:0/12 Commit:12
 
 # Let 2 campaign. It should succeed, since it's up-to-date on the log.
 campaign 2
@@ -223,17 +223,17 @@ stabilize
   Entries:
   2/13 EntryNormal ""
   Messages:
-  1->2 MsgAppResp Term:2 Log:0/13
+  1->2 MsgAppResp Term:2 Log:0/13 Commit:12
 > 3 handling Ready
   Ready MustSync=true:
   Lead:2 State:StateFollower
   Entries:
   2/13 EntryNormal ""
   Messages:
-  3->2 MsgAppResp Term:2 Log:0/13
+  3->2 MsgAppResp Term:2 Log:0/13 Commit:12
 > 2 receiving messages
-  1->2 MsgAppResp Term:2 Log:0/13
-  3->2 MsgAppResp Term:2 Log:0/13
+  1->2 MsgAppResp Term:2 Log:0/13 Commit:12
+  3->2 MsgAppResp Term:2 Log:0/13 Commit:12
 > 2 handling Ready
   Ready MustSync=false:
   HardState Term:2 Vote:2 Commit:13
@@ -252,14 +252,14 @@ stabilize
   CommittedEntries:
   2/13 EntryNormal ""
   Messages:
-  1->2 MsgAppResp Term:2 Log:0/13
+  1->2 MsgAppResp Term:2 Log:0/13 Commit:13
 > 3 handling Ready
   Ready MustSync=false:
   HardState Term:2 Vote:2 Commit:13
   CommittedEntries:
   2/13 EntryNormal ""
   Messages:
-  3->2 MsgAppResp Term:2 Log:0/13
+  3->2 MsgAppResp Term:2 Log:0/13 Commit:13
 > 2 receiving messages
-  1->2 MsgAppResp Term:2 Log:0/13
-  3->2 MsgAppResp Term:2 Log:0/13
+  1->2 MsgAppResp Term:2 Log:0/13 Commit:13
+  3->2 MsgAppResp Term:2 Log:0/13 Commit:13
diff --git a/testdata/prevote_checkquorum.txt b/testdata/prevote_checkquorum.txt
index 6db6662b..a7cc57ae 100644
--- a/testdata/prevote_checkquorum.txt
+++ b/testdata/prevote_checkquorum.txt
@@ -147,17 +147,17 @@ stabilize
   Entries:
   2/12 EntryNormal ""
   Messages:
-  1->3 MsgAppResp Term:2 Log:0/12
+  1->3 MsgAppResp Term:2 Log:0/12 Commit:11
 > 2 handling Ready
   Ready MustSync=true:
   Lead:3 State:StateFollower
   Entries:
   2/12 EntryNormal ""
   Messages:
-  2->3 MsgAppResp Term:2 Log:0/12
+  2->3 MsgAppResp Term:2 Log:0/12 Commit:11
 > 3 receiving messages
-  1->3 MsgAppResp Term:2 Log:0/12
-  2->3 MsgAppResp Term:2 Log:0/12
+  1->3 MsgAppResp Term:2 Log:0/12 Commit:11
+  2->3 MsgAppResp Term:2 Log:0/12 Commit:11
 > 3 handling Ready
   Ready MustSync=false:
   HardState Term:2 Vote:3 Commit:12
@@ -176,17 +176,17 @@ stabilize
   CommittedEntries:
   2/12 EntryNormal ""
   Messages:
-  1->3 MsgAppResp Term:2 Log:0/12
+  1->3 MsgAppResp Term:2 Log:0/12 Commit:12
 > 2 handling Ready
   Ready MustSync=false:
   HardState Term:2 Vote:3 Commit:12
   CommittedEntries:
   2/12 EntryNormal ""
   Messages:
-  2->3 MsgAppResp Term:2 Log:0/12
+  2->3 MsgAppResp Term:2 Log:0/12 Commit:12
 > 3 receiving messages
-  1->3 MsgAppResp Term:2 Log:0/12
-  2->3 MsgAppResp Term:2 Log:0/12
+  1->3 MsgAppResp Term:2 Log:0/12 Commit:12
+  2->3 MsgAppResp Term:2 Log:0/12 Commit:12
 
 # Node 3 is now the leader. Even though the leader is active, nodes 1 and 2 can
 # still win a prevote and election if they both explicitly campaign, since the
@@ -302,7 +302,7 @@ stabilize
   Entries:
   3/13 EntryNormal ""
   Messages:
-  1->2 MsgAppResp Term:3 Log:0/13
+  1->2 MsgAppResp Term:3 Log:0/13 Commit:12
 > 3 handling Ready
   Ready MustSync=true:
   Lead:2 State:StateFollower
@@ -310,10 +310,10 @@ stabilize
   Entries:
   3/13 EntryNormal ""
   Messages:
-  3->2 MsgAppResp Term:3 Log:0/13
+  3->2 MsgAppResp Term:3 Log:0/13 Commit:12
 > 2 receiving messages
-  1->2 MsgAppResp Term:3 Log:0/13
-  3->2 MsgAppResp Term:3 Log:0/13
+  1->2 MsgAppResp Term:3 Log:0/13 Commit:12
+  3->2 MsgAppResp Term:3 Log:0/13 Commit:12
 > 2 handling Ready
   Ready MustSync=false:
   HardState Term:3 Vote:2 Commit:13
@@ -332,14 +332,14 @@ stabilize
   CommittedEntries:
   3/13 EntryNormal ""
   Messages:
-  1->2 MsgAppResp Term:3 Log:0/13
+  1->2 MsgAppResp Term:3 Log:0/13 Commit:13
 > 3 handling Ready
   Ready MustSync=false:
   HardState Term:3 Commit:13
   CommittedEntries:
   3/13 EntryNormal ""
   Messages:
-  3->2 MsgAppResp Term:3 Log:0/13
+  3->2 MsgAppResp Term:3 Log:0/13 Commit:13
 > 2 receiving messages
-  1->2 MsgAppResp Term:3 Log:0/13
-  3->2 MsgAppResp Term:3 Log:0/13
+  1->2 MsgAppResp Term:3 Log:0/13 Commit:13
+  3->2 MsgAppResp Term:3 Log:0/13 Commit:13
diff --git a/testdata/probe_and_replicate.txt b/testdata/probe_and_replicate.txt
index d970183c..05f17a13 100644
--- a/testdata/probe_and_replicate.txt
+++ b/testdata/probe_and_replicate.txt
@@ -510,9 +510,9 @@ stabilize 1 2
   6/20 EntryNormal "prop_6_20"
   8/21 EntryNormal ""
   Messages:
-  2->1 MsgAppResp Term:8 Log:0/21
+  2->1 MsgAppResp Term:8 Log:0/21 Commit:18
 > 1 receiving messages
-  2->1 MsgAppResp Term:8 Log:0/21
+  2->1 MsgAppResp Term:8 Log:0/21 Commit:18
 
 stabilize 1 3
 ----
@@ -564,9 +564,9 @@ stabilize 1 3
   5/17 EntryNormal "prop_5_17"
   6/18 EntryNormal ""
   Messages:
-  3->1 MsgAppResp Term:8 Log:0/21
+  3->1 MsgAppResp Term:8 Log:0/21 Commit:18
 > 1 receiving messages
-  3->1 MsgAppResp Term:8 Log:0/21
+  3->1 MsgAppResp Term:8 Log:0/21 Commit:18
 
 stabilize 1 4
 ----
@@ -580,9 +580,9 @@ stabilize 1 4
   Entries:
   8/21 EntryNormal ""
   Messages:
-  4->1 MsgAppResp Term:8 Log:0/21
+  4->1 MsgAppResp Term:8 Log:0/21 Commit:18
 > 1 receiving messages
-  4->1 MsgAppResp Term:8 Log:0/21
+  4->1 MsgAppResp Term:8 Log:0/21 Commit:18
 > 1 handling Ready
   Ready MustSync=false:
   HardState Term:8 Vote:1 Commit:21
@@ -604,9 +604,9 @@ stabilize 1 4
   6/20 EntryNormal "prop_6_20"
   8/21 EntryNormal ""
   Messages:
-  4->1 MsgAppResp Term:8 Log:0/21
+  4->1 MsgAppResp Term:8 Log:0/21 Commit:21
 > 1 receiving messages
-  4->1 MsgAppResp Term:8 Log:0/21
+  4->1 MsgAppResp Term:8 Log:0/21 Commit:21
 
 stabilize 1 5
 ----
@@ -647,9 +647,9 @@ stabilize 1 5
   6/20 EntryNormal "prop_6_20"
   8/21 EntryNormal ""
   Messages:
-  5->1 MsgAppResp Term:8 Log:0/21
+  5->1 MsgAppResp Term:8 Log:0/21 Commit:21
 > 1 receiving messages
-  5->1 MsgAppResp Term:8 Log:0/21
+  5->1 MsgAppResp Term:8 Log:0/21 Commit:21
 
 stabilize 1 6
 ----
@@ -702,9 +702,9 @@ stabilize 1 6
   6/20 EntryNormal "prop_6_20"
   8/21 EntryNormal ""
   Messages:
-  6->1 MsgAppResp Term:8 Log:0/21
+  6->1 MsgAppResp Term:8 Log:0/21 Commit:21
 > 1 receiving messages
-  6->1 MsgAppResp Term:8 Log:0/21
+  6->1 MsgAppResp Term:8 Log:0/21 Commit:21
 
 stabilize 1 7
 ----
@@ -765,6 +765,6 @@ stabilize 1 7
   6/20 EntryNormal "prop_6_20"
   8/21 EntryNormal ""
   Messages:
-  7->1 MsgAppResp Term:8 Log:0/21
+  7->1 MsgAppResp Term:8 Log:0/21 Commit:21
 > 1 receiving messages
-  7->1 MsgAppResp Term:8 Log:0/21
+  7->1 MsgAppResp Term:8 Log:0/21 Commit:21
diff --git a/tracker/progress.go b/tracker/progress.go
index 1b594cf3..905dfedc 100644
--- a/tracker/progress.go
+++ b/tracker/progress.go
@@ -30,6 +30,8 @@ import (
 type Progress struct {
 	// Match is the index up to which the follower's log is known to match the
 	// leader's.
+	//
+	// Match does not regress.
 	Match uint64
 	// Next is the log index of the next entry to send to this follower. All
 	// entries with indices in (Match, Next) interval are already in flight.
@@ -40,8 +42,16 @@ type Progress struct {
 	// In StateSnapshot, Next == PendingSnapshot + 1.
 	Next uint64
 
+	// Commit is the known commit index of the follower's log.
+	//
+	// Invariant: Commit <= Match.
+	// Invariant: Commit <= leader's commit index.
+	// Commit does not regress.
+	Commit uint64
 	// sentCommit is the highest commit index in flight to the follower.
 	//
+	// Invariant: sentCommit >= Commit.
+	//
 	// In StateSnapshot, sentCommit == PendingSnapshot == Next-1.
 	sentCommit uint64
 
@@ -196,6 +206,11 @@ func (pr *Progress) SentCommit(commit uint64) {
 	pr.sentCommit = commit
 }
 
+// UpdateCommit moves the known commit index for this follower forward.
+func (pr *Progress) UpdateCommit(index uint64) {
+	pr.Commit = max(pr.Commit, min(index, pr.Match))
+}
+
 // MaybeUpdate is called when an MsgAppResp arrives from the follower, with the
 // index acked by it. The method returns false if the given n index comes from
 // an outdated message. Otherwise it updates the progress and returns true.