From da6ad00455b36686a60003784ac617b36edbed3a Mon Sep 17 00:00:00 2001
From: Pavel Kalinnikov <pavel@cockroachlabs.com>
Date: Wed, 24 Jan 2024 09:20:01 +0000
Subject: [PATCH] raft,tracker: track commit index of each follower

Signed-off-by: Pavel Kalinnikov <pavel@cockroachlabs.com>
---
 raft.go                                       |  11 +-
 testdata/async_storage_writes.txt             | 142 +++++++++---------
 .../async_storage_writes_append_aba_race.txt  |  18 +--
 testdata/campaign.txt                         |  16 +-
 testdata/campaign_learner_must_vote.txt       |   8 +-
 testdata/checkquorum.txt                      |  16 +-
 testdata/confchange_v1_add_single.txt         |   4 +-
 testdata/confchange_v1_remove_leader.txt      |  48 +++---
 .../confchange_v1_remove_leader_stepdown.txt  |  40 ++---
 testdata/confchange_v2_add_double_auto.txt    |  76 +++++-----
 .../confchange_v2_add_double_implicit.txt     |   8 +-
 testdata/confchange_v2_add_single_auto.txt    |   4 +-
 .../confchange_v2_add_single_explicit.txt     |  28 ++--
 testdata/confchange_v2_replace_leader.txt     |  72 ++++-----
 .../confchange_v2_replace_leader_stepdown.txt |  24 +--
 .../forget_leader_prevote_checkquorum.txt     |   2 +-
 .../heartbeat_resp_recovers_from_probing.txt  |   4 +-
 testdata/prevote.txt                          |  32 ++--
 testdata/prevote_checkquorum.txt              |  32 ++--
 testdata/probe_and_replicate.txt              |  48 +++---
 testdata/snapshot_succeed_via_app_resp.txt    |   4 +-
 tracker/progress.go                           |  11 ++
 22 files changed, 331 insertions(+), 317 deletions(-)

diff --git a/raft.go b/raft.go
index 5a150562..8c76573d 100644
--- a/raft.go
+++ b/raft.go
@@ -815,7 +815,7 @@ 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
 }
 
@@ -1465,6 +1465,7 @@ func stepLeader(r *raft, m pb.Message) error {
 				r.sendAppend(m.From)
 			}
 		} else {
+			pr.UpdateCommit(m.Commit)
 			oldPaused := pr.IsPaused()
 			// We want to update our tracking if the response updates our
 			// matched index or if the response can move a probing peer back
@@ -1505,6 +1506,8 @@ func stepLeader(r *raft, m pb.Message) error {
 				} else if oldPaused {
 					// If we were paused before, this node may be missing the
 					// latest commit index, so send it.
+					// TODO(pav-kv): remove this branch, and decide on sending the commit
+					// index update based on pr.Commit.
 					r.sendAppend(m.From)
 				}
 				// We've updated flow control information above, which may
@@ -1730,12 +1733,12 @@ func stepFollower(r *raft, m pb.Message) error {
 }
 
 func (r *raft) handleAppendEntries(m pb.Message) {
-	if m.Index < r.raftLog.committed {
-		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: r.raftLog.committed})
+	if committed := r.raftLog.committed; m.Index < committed {
+		r.send(pb.Message{To: m.From, Type: pb.MsgAppResp, Index: committed, Commit: committed})
 		return
 	}
 	if mlastIndex, ok := r.raftLog.maybeAppend(m.Index, m.LogTerm, m.Commit, m.Entries...); 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: m.Commit})
 		return
 	}
 	r.logger.Debugf("%x [logterm: %d, index: %d] rejected MsgApp [logterm: %d, index: %d] from %x",
diff --git a/testdata/async_storage_writes.txt b/testdata/async_storage_writes.txt
index 52f37092..13fb015f 100644
--- a/testdata/async_storage_writes.txt
+++ b/testdata/async_storage_writes.txt
@@ -83,7 +83,7 @@ stabilize
   Messages:
   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, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/11]
+  1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/11 EntryNormal ""] Responses:[1->1 MsgAppResp Term:1 Log:0/11 Commit:10, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/11]
 > 2 receiving messages
   1->2 MsgApp Term:1 Log:1/10 Commit:10 Entries:[1/11 EntryNormal ""]
 > 3 receiving messages
@@ -92,7 +92,7 @@ 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:
@@ -100,32 +100,32 @@ stabilize
   Entries:
   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, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/11]
+  2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/11 EntryNormal ""] Responses:[2->1 MsgAppResp Term:1 Log:0/11 Commit:10, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/11]
 > 3 handling Ready
   Ready MustSync=true:
   Lead:1 State:StateFollower
   Entries:
   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, AppendThread->3 MsgStorageAppendResp Term:1 Log:1/11]
+  3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/11 EntryNormal ""] Responses:[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
@@ -159,7 +159,7 @@ stabilize
   CommittedEntries:
   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->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:11 Vote:1 Responses:[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 ""]]
 > 3 handling Ready
   Ready MustSync=false:
@@ -167,7 +167,7 @@ stabilize
   CommittedEntries:
   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->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:11 Vote:1 Responses:[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 ""]]
 > 1 receiving messages
   ApplyThread->1 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/11 EntryNormal ""]
@@ -175,12 +175,12 @@ 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 ""]
@@ -192,8 +192,8 @@ 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
@@ -212,7 +212,7 @@ process-ready 1 2 3
   Messages:
   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, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/12]
+  1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"] Responses:[1->1 MsgAppResp Term:1 Log:0/12 Commit:11, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/12]
 > 2 handling Ready
   <empty Ready>
 > 3 handling Ready
@@ -232,13 +232,13 @@ process-ready 1 2 3
   Entries:
   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, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/12]
+  2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"] Responses:[2->1 MsgAppResp Term:1 Log:0/12 Commit:11, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/12]
 > 3 handling Ready
   Ready MustSync=true:
   Entries:
   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, AppendThread->3 MsgStorageAppendResp Term:1 Log:1/12]
+  3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"] Responses:[3->1 MsgAppResp Term:1 Log:0/12 Commit:11, AppendThread->3 MsgStorageAppendResp Term:1 Log:1/12]
 
 propose 1 prop_2
 ----
@@ -253,7 +253,7 @@ process-ready 1 2 3
   Messages:
   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, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/13]
+  1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"] Responses:[1->1 MsgAppResp Term:1 Log:0/13 Commit:11, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/13]
 > 2 handling Ready
   <empty Ready>
 > 3 handling Ready
@@ -273,13 +273,13 @@ process-ready 1 2 3
   Entries:
   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, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/13]
+  2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"] Responses:[2->1 MsgAppResp Term:1 Log:0/13 Commit:11, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/13]
 > 3 handling Ready
   Ready MustSync=true:
   Entries:
   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, AppendThread->3 MsgStorageAppendResp Term:1 Log:1/13]
+  3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"] Responses:[3->1 MsgAppResp Term:1 Log:0/13 Commit:11, AppendThread->3 MsgStorageAppendResp Term:1 Log:1/13]
 
 process-append-thread 1 2 3
 ----
@@ -287,27 +287,27 @@ 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
 
@@ -329,7 +329,7 @@ process-ready 1 2 3
   1->3 MsgApp Term:1 Log:1/13 Commit:12
   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, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/14]
+  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 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:[ApplyThread->1 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"]]
 > 2 handling Ready
   <empty Ready>
@@ -355,7 +355,7 @@ process-ready 1 2 3
   CommittedEntries:
   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, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/14]
+  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 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:[ApplyThread->2 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"]]
 > 3 handling Ready
   Ready MustSync=true:
@@ -365,7 +365,7 @@ process-ready 1 2 3
   CommittedEntries:
   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, AppendThread->3 MsgStorageAppendResp Term:1 Log:1/14]
+  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 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:[ApplyThread->3 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/12 EntryNormal "prop_1"]]
 
 process-append-thread 1 2 3
@@ -374,27 +374,27 @@ 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
 
@@ -416,7 +416,7 @@ process-ready 1 2 3
   1->3 MsgApp Term:1 Log:1/14 Commit:13
   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, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/15]
+  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 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:[ApplyThread->1 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"]]
 > 2 handling Ready
   <empty Ready>
@@ -442,7 +442,7 @@ process-ready 1 2 3
   CommittedEntries:
   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, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/15]
+  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 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:[ApplyThread->2 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"]]
 > 3 handling Ready
   Ready MustSync=true:
@@ -452,7 +452,7 @@ process-ready 1 2 3
   CommittedEntries:
   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, AppendThread->3 MsgStorageAppendResp Term:1 Log:1/15]
+  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 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:[ApplyThread->3 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/13 EntryNormal "prop_2"]]
 
 process-append-thread 1 2 3
@@ -461,21 +461,21 @@ 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
@@ -498,12 +498,12 @@ 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"]
@@ -542,7 +542,7 @@ process-ready 1 2 3
   CommittedEntries:
   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, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/15]
+  2->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:14 Vote:1 Responses:[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:[ApplyThread->2 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/14 EntryNormal "prop_3"]]
 > 3 handling Ready
   Ready MustSync=false:
@@ -550,7 +550,7 @@ process-ready 1 2 3
   CommittedEntries:
   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, AppendThread->3 MsgStorageAppendResp Term:1 Log:1/15]
+  3->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:14 Vote:1 Responses:[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:[ApplyThread->3 MsgStorageApplyResp Term:0 Log:0/0 Entries:[1/14 EntryNormal "prop_3"]]
 
 process-append-thread 1 2 3
@@ -559,21 +559,21 @@ 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
@@ -596,12 +596,12 @@ 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"]
@@ -640,7 +640,7 @@ process-ready 1 2 3
   CommittedEntries:
   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->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:15 Vote:1 Responses:[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"]]
 > 3 handling Ready
   Ready MustSync=false:
@@ -648,7 +648,7 @@ process-ready 1 2 3
   CommittedEntries:
   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->AppendThread MsgStorageAppend Term:1 Log:0/0 Commit:15 Vote:1 Responses:[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"]]
 
 process-append-thread 2 3
@@ -657,13 +657,13 @@ 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
@@ -686,8 +686,8 @@ 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
@@ -711,12 +711,12 @@ 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
 ----
@@ -738,8 +738,8 @@ 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 4b68330f..399800e8 100644
--- a/testdata/async_storage_writes_append_aba_race.txt
+++ b/testdata/async_storage_writes_append_aba_race.txt
@@ -42,7 +42,7 @@ Messages:
 2->5 MsgApp Term:1 Log:1/11 Commit:11 Entries:[1/12 EntryNormal "init_prop"]
 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, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/12]
+2->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "init_prop"] Responses:[2->2 MsgAppResp Term:1 Log:0/12 Commit:11, AppendThread->2 MsgStorageAppendResp Term:1 Log:1/12]
 
 deliver-msgs 1 drop=(3,4,5,6,7)
 ----
@@ -61,7 +61,7 @@ Ready MustSync=true:
 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, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/12]
+1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[1/12 EntryNormal "init_prop"] Responses:[1->2 MsgAppResp Term:1 Log:0/12 Commit:11, AppendThread->1 MsgStorageAppendResp Term:1 Log:1/12]
 
 # Step 4: node 3 becomes the leader after getting a vote from nodes 4, 5, and 6.
 
@@ -183,7 +183,7 @@ Messages:
 3->5 MsgApp Term:2 Log:1/11 Commit:11 Entries:[2/12 EntryNormal ""]
 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, AppendThread->3 MsgStorageAppendResp Term:2 Log:2/12]
+3->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[2/12 EntryNormal ""] Responses:[3->3 MsgAppResp Term:2 Log:0/12 Commit:11, AppendThread->3 MsgStorageAppendResp Term:2 Log:2/12]
 
 deliver-msgs 1 drop=(2,4,5,6,7)
 ----
@@ -210,7 +210,7 @@ HardState Term:2 Commit:11
 Entries:
 2/12 EntryNormal ""
 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, AppendThread->1 MsgStorageAppendResp Term:2 Log:2/12]
+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 Commit:11, AppendThread->1 MsgStorageAppendResp Term:2 Log:2/12]
 
 # Step 6: node 3 crashes and node 4 becomes leader getting the vote from 5, 6, and 7.
 
@@ -325,7 +325,7 @@ Messages:
 4->5 MsgApp Term:3 Log:1/11 Commit:11 Entries:[3/12 EntryNormal ""]
 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, AppendThread->4 MsgStorageAppendResp Term:3 Log:3/12]
+4->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[3/12 EntryNormal ""] Responses:[4->4 MsgAppResp Term:3 Log:0/12 Commit:11, AppendThread->4 MsgStorageAppendResp Term:3 Log:3/12]
 
 # Step 7: before the new entries reach node 1, it hears of the term change
 # through a heartbeat and persists the new term. Node 1 then receives these
@@ -390,7 +390,7 @@ Ready MustSync=true:
 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, AppendThread->1 MsgStorageAppendResp Term:3 Log:3/12]
+1->AppendThread MsgStorageAppend Term:0 Log:0/0 Entries:[3/12 EntryNormal ""] Responses:[1->4 MsgAppResp Term:3 Log:0/12 Commit:11, AppendThread->1 MsgStorageAppendResp Term:3 Log:3/12]
 
 # Step 8: The asynchronous log appends from the first Ready complete and the
 # MsgStorageAppendResp is returned to the raft node state machine. A decision
@@ -405,7 +405,7 @@ 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
@@ -432,7 +432,7 @@ 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
@@ -467,7 +467,7 @@ 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 85617df3..734422b8 100644
--- a/testdata/campaign_learner_must_vote.txt
+++ b/testdata/campaign_learner_must_vote.txt
@@ -129,10 +129,10 @@ 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
@@ -148,6 +148,6 @@ 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_add_single.txt b/testdata/confchange_v1_add_single.txt
index 0419d28d..e9469ed7 100644
--- a/testdata/confchange_v1_add_single.txt
+++ b/testdata/confchange_v1_add_single.txt
@@ -101,6 +101,6 @@ stabilize
 > 2 handling Ready
   Ready MustSync=false:
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:4
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:4
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 5cf4f24c..78b5a2bc 100644
--- a/testdata/confchange_v2_add_double_auto.txt
+++ b/testdata/confchange_v2_add_double_auto.txt
@@ -126,9 +126,9 @@ 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
@@ -145,10 +145,10 @@ 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
@@ -198,9 +198,9 @@ stabilize 1 3
 > 3 handling Ready
   Ready MustSync=false:
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/5
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:5
 > 1 receiving messages
-  3->1 MsgAppResp Term:1 Log:0/5
+  3->1 MsgAppResp Term:1 Log:0/5 Commit:5
 
 # Nothing else happens.
 stabilize
@@ -238,13 +238,13 @@ 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
@@ -272,8 +272,8 @@ 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
@@ -315,10 +315,10 @@ 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:
@@ -330,10 +330,10 @@ 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
@@ -342,14 +342,14 @@ 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
@@ -381,9 +381,9 @@ 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:
@@ -393,20 +393,20 @@ 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 81b3f0de..7d27151f 100644
--- a/testdata/confchange_v2_add_double_implicit.txt
+++ b/testdata/confchange_v2_add_double_implicit.txt
@@ -109,9 +109,9 @@ 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
@@ -128,7 +128,7 @@ 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_auto.txt b/testdata/confchange_v2_add_single_auto.txt
index fe127bf5..666ddb52 100644
--- a/testdata/confchange_v2_add_single_auto.txt
+++ b/testdata/confchange_v2_add_single_auto.txt
@@ -102,6 +102,6 @@ stabilize
 > 2 handling Ready
   Ready MustSync=false:
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:4
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:4
diff --git a/testdata/confchange_v2_add_single_explicit.txt b/testdata/confchange_v2_add_single_explicit.txt
index c51900f0..4c83d5f1 100644
--- a/testdata/confchange_v2_add_single_explicit.txt
+++ b/testdata/confchange_v2_add_single_explicit.txt
@@ -102,9 +102,9 @@ stabilize 1 2
 > 2 handling Ready
   Ready MustSync=false:
   Messages:
-  2->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:4
 > 1 receiving messages
-  2->1 MsgAppResp Term:1 Log:0/4
+  2->1 MsgAppResp Term:1 Log:0/4 Commit:4
 
 # Check that we're not allowed to change membership again while in the joint state.
 # This leads to an empty entry being proposed instead (index 5 in the stabilize block
@@ -139,11 +139,11 @@ 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
@@ -164,12 +164,12 @@ 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
@@ -192,9 +192,9 @@ 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
@@ -210,6 +210,6 @@ 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 dfb09505..4e2bf5cb 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]
@@ -150,9 +150,9 @@ stabilize
 > 4 handling Ready
   Ready MustSync=false:
   Messages:
-  4->1 MsgAppResp Term:1 Log:0/4
+  4->1 MsgAppResp Term:1 Log:0/4 Commit:4
 > 1 receiving messages
-  4->1 MsgAppResp Term:1 Log:0/4
+  4->1 MsgAppResp Term:1 Log:0/4 Commit:4
 
 
 # Transfer leadership while in the joint config.
@@ -257,25 +257,25 @@ 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
@@ -299,27 +299,27 @@ stabilize
   CommittedEntries:
   2/5 EntryNormal ""
   Messages:
-  1->4 MsgAppResp Term:2 Log:0/5
-  1->4 MsgAppResp Term:2 Log:0/5
+  1->4 MsgAppResp Term:2 Log:0/5 Commit:4
+  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
-  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
+  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
@@ -356,23 +356,23 @@ 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
@@ -395,7 +395,7 @@ 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:
@@ -403,7 +403,7 @@ 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:
@@ -411,13 +411,13 @@ 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/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 d5829704..715417ed 100644
--- a/testdata/probe_and_replicate.txt
+++ b/testdata/probe_and_replicate.txt
@@ -504,9 +504,9 @@ 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
 > 1 handling Ready
   Ready MustSync=false:
   Messages:
@@ -516,9 +516,9 @@ stabilize 1 2
 > 2 handling Ready
   Ready MustSync=false:
   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
 ----
@@ -554,9 +554,9 @@ 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
 > 1 handling Ready
   Ready MustSync=false:
   Messages:
@@ -566,9 +566,9 @@ stabilize 1 3
 > 3 handling Ready
   Ready MustSync=false:
   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
 ----
@@ -582,9 +582,9 @@ 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
@@ -606,9 +606,9 @@ 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
 ----
@@ -641,9 +641,9 @@ 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
 > 1 handling Ready
   Ready MustSync=false:
   Messages:
@@ -653,9 +653,9 @@ stabilize 1 5
 > 5 handling Ready
   Ready MustSync=false:
   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
 ----
@@ -694,9 +694,9 @@ 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
 > 1 handling Ready
   Ready MustSync=false:
   Messages:
@@ -706,9 +706,9 @@ stabilize 1 6
 > 6 handling Ready
   Ready MustSync=false:
   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
 ----
@@ -751,9 +751,9 @@ 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
 > 1 handling Ready
   Ready MustSync=false:
   Messages:
@@ -763,6 +763,6 @@ stabilize 1 7
 > 7 handling Ready
   Ready MustSync=false:
   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/testdata/snapshot_succeed_via_app_resp.txt b/testdata/snapshot_succeed_via_app_resp.txt
index 80ed3646..37917403 100644
--- a/testdata/snapshot_succeed_via_app_resp.txt
+++ b/testdata/snapshot_succeed_via_app_resp.txt
@@ -150,7 +150,7 @@ stabilize
 > 3 handling Ready
   Ready MustSync=false:
   Messages:
-  3->1 MsgAppResp Term:1 Log:0/11
+  3->1 MsgAppResp Term:1 Log:0/11 Commit:11
 > 1 receiving messages
   2->1 MsgHeartbeatResp Term:1 Log:0/0
-  3->1 MsgAppResp Term:1 Log:0/11
+  3->1 MsgAppResp Term:1 Log:0/11 Commit:11
diff --git a/tracker/progress.go b/tracker/progress.go
index b4d07deb..e80059f5 100644
--- a/tracker/progress.go
+++ b/tracker/progress.go
@@ -30,9 +30,13 @@ import (
 type Progress struct {
 	// Match is log index up to which the follower's log matches the leader's.
 	Match uint64
+	// Commit is the commit index of the follower's log.
+	// INVARIANT: Commit <= Match.
+	Commit uint64
 	// Next is the index of the next log entry to be sent to the follower. Entries
 	// in the (Match, Next) interval are on the fly to this follower.
 	Next uint64
+
 	// State defines how the leader should interact with the follower.
 	//
 	// When in StateProbe, leader sends at most one replication message
@@ -180,6 +184,13 @@ func (pr *Progress) UpdateOnEntriesSend(entries int, bytes, nextIndex uint64) er
 	return nil
 }
 
+// UpdateCommit moves the known commit index for this follower forward.
+func (pr *Progress) UpdateCommit(index uint64) {
+	if index > pr.Commit {
+		pr.Commit = index
+	}
+}
+
 // 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.