raft: rename Progress.last to match_index

src/bin/toysql.rs

@@ -118,7 +118,7 @@ The following commands are also available:
  let status = self.client.status()?;
  let mut node_logs = status
  .raft
- .last_index
+ .match_index
  .iter()
  .map(|(id, index)| format!("{}:{}", id, index))
  .collect::<Vec<_>>();
@@ -134,7 +134,7 @@ Storage: {keys} keys, {logical_size} MB logical, {nodes}x {disk_size} MB disk,
  server = status.server,
  leader = status.raft.leader,
  term = status.raft.term,
- nodes = status.raft.last_index.len(),
+ nodes = status.raft.match_index.len(),
  committed = status.raft.commit_index,
  applied = status.raft.apply_index,
  raft_storage = status.raft.storage.name,

src/raft/message.rs

@@ -175,11 +175,9 @@ pub struct Status {
  pub leader: NodeID,
  /// The current Raft term.
  pub term: Term,
- /// The last log indexes of all nodes. Use a BTreeMap for deterministic
+ /// The match indexes of all nodes. Use a BTreeMap for deterministic
  /// debug output.
- ///
- /// TODO: rename to match.
- pub last_index: BTreeMap<NodeID, Index>,
+ pub match_index: BTreeMap<NodeID, Index>,
  /// The current commit index.
  pub commit_index: Index,
  /// The current applied index.

src/raft/node.rs

@@ -681,16 +681,13 @@ impl RawNode<Follower> {
  }
 }
 
-/// Peer replication progress.
+/// Follower replication progress.
 #[derive(Clone, Debug, PartialEq)]
 struct Progress {
- /// The next index to replicate to the peer.
- next: Index,
- /// The last index known to be replicated to the peer.
- ///
- /// TODO: rename to match. It needs to track the position where the
- /// follower's log matches the leader's, not its last position.
- last: Index,
+ /// The next index to replicate to the follower.
+ next_index: Index,
+ /// The last index where the follower's log matches the leader.
+ match_index: Index,
  /// The last read sequence number confirmed by the peer.
  read_seq: ReadSequence,
 }
@@ -720,7 +717,7 @@ struct Read {
 // A leader serves requests and replicates the log to followers.
 #[derive(Clone, Debug, PartialEq)]
 pub struct Leader {
- /// Peer replication progress.
+ /// Follower replication progress.
  progress: HashMap<NodeID, Progress>,
  /// Keeps track of pending write requests, keyed by log index. These are
  /// added when the write is proposed and appended to the leader's log, and
@@ -749,9 +746,11 @@ pub struct Leader {
 impl Leader {
  /// Creates a new leader role.
  fn new(peers: HashSet<NodeID>, last_index: Index) -> Self {
- let next = last_index + 1;
- let progress =
- peers.into_iter().map(|p| (p, Progress { next, last: 0, read_seq: 0 })).collect();
+ let next_index = last_index + 1;
+ let progress = peers
+ .into_iter()
+ .map(|p| (p, Progress { next_index, match_index: 0, read_seq: 0 }))
+ .collect();
  Self {
  progress,
  writes: HashMap::new(),
@@ -859,11 +858,12 @@ impl RawNode<Leader> {
  Message::AppendResponse { reject_index: 0, last_index, last_term } => {
  let (li, lt) = self.log.get_last_index();
  assert!(last_index <= li && last_term <= lt, "follower appended future entries");
+ debug_assert!(self.log.has(last_index, last_term)?, "follower has unknown tail");
 
  let progress = self.role.progress.get_mut(&msg.from).expect("unknown node");
- if last_index > progress.last {
- progress.last = last_index;
- progress.next = last_index + 1;
+ if last_index > progress.match_index {
+ progress.match_index = last_index;
+ progress.next_index = last_index + 1;
  self.maybe_commit_and_apply()?;
  }
  }
@@ -880,8 +880,8 @@ impl RawNode<Leader> {
  // If the next index was rejected, try the previous one.
  // Otherwise, the rejection is stale and can be ignored. If the
  // follower's log is shorter, skip straight to its last index.
- if progress.next == reject_index + 1 {
- progress.next = std::cmp::min(progress.next - 1, last_index + 1);
+ if progress.next_index == reject_index + 1 {
+ progress.next_index = std::cmp::min(progress.next_index - 1, last_index + 1);
  self.send_log(msg.from)?;
  }
  }
@@ -918,11 +918,11 @@ impl RawNode<Leader> {
  let status = Status {
  leader: self.id,
  term: self.term,
- last_index: self
+ match_index: self
  .role
  .progress
  .iter()
- .map(|(id, p)| (*id, p.last))
+ .map(|(id, p)| (*id, p.match_index))
  .chain(std::iter::once((self.id, self.log.get_last_index().0)))
  .sorted()
  .collect(),
@@ -993,7 +993,7 @@ impl RawNode<Leader> {
  self.role
  .progress
  .values()
- .map(|p| p.last)
+ .map(|p| p.match_index)
  .chain(std::iter::once(self.log.get_last_index().0))
  .collect(),
  );
@@ -1073,10 +1073,12 @@ impl RawNode<Leader> {
  /// Sends pending log entries to a peer.
  fn send_log(&mut self, peer: NodeID) -> Result<()> {
  let (base_index, base_term) = match self.role.progress.get(&peer) {
- Some(Progress { next, .. }) if *next > 1 => match self.log.get(next - 1)? {
- Some(entry) => (entry.index, entry.term),
- None => panic!("missing base entry {}", next - 1),
- },
+ Some(Progress { next_index, .. }) if *next_index > 1 => {
+ match self.log.get(next_index - 1)? {
+ Some(entry) => (entry.index, entry.term),
+ None => panic!("missing base entry {}", next_index - 1),
+ }
+ }
  Some(_) => (0, 0),
  None => panic!("unknown peer {}", peer),
  };
@@ -1643,7 +1645,7 @@ mod tests {
  .progress
  .iter()
  .sorted_by_key(|(id, _)| *id)
- .map(|(id, pr)| format!("{id}:{}→{}", pr.last, pr.next))
+ .map(|(id, pr)| format!("{id}:{}→{}", pr.match_index, pr.next_index))
  .join(" ")
  ))
  }

src/raft/testscripts/node/request_status

@@ -25,11 +25,11 @@ status request=true 1
 stabilize
 ---
 c1@1 → n1 ClientRequest id=0x02 status
-n1@1 → c1 ClientResponse id=0x02 status Status { leader: 1, term: 1, last_index: {1: 2, 2: 2, 3: 1}, commit_index: 2, apply_index: 2, storage: Status { name: "memory", keys: 4, size: 41, total_disk_size: 0, live_disk_size: 0, garbage_disk_size: 0 } }
+n1@1 → c1 ClientResponse id=0x02 status Status { leader: 1, term: 1, match_index: {1: 2, 2: 2, 3: 1}, commit_index: 2, apply_index: 2, storage: Status { name: "memory", keys: 4, size: 41, total_disk_size: 0, live_disk_size: 0, garbage_disk_size: 0 } }
 c1@1 status ⇒ Status {
  leader: 1,
  term: 1,
- last_index: {
+ match_index: {
  1: 2,
  2: 2,
  3: 1,
@@ -52,12 +52,12 @@ stabilize
 ---
 c2@1 → n2 ClientRequest id=0x03 status
 n2@1 → n1 ClientRequest id=0x03 status
-n1@1 → n2 ClientResponse id=0x03 status Status { leader: 1, term: 1, last_index: {1: 2, 2: 2, 3: 1}, commit_index: 2, apply_index: 2, storage: Status { name: "memory", keys: 4, size: 41, total_disk_size: 0, live_disk_size: 0, garbage_disk_size: 0 } }
-n2@1 → c2 ClientResponse id=0x03 status Status { leader: 1, term: 1, last_index: {1: 2, 2: 2, 3: 1}, commit_index: 2, apply_index: 2, storage: Status { name: "memory", keys: 4, size: 41, total_disk_size: 0, live_disk_size: 0, garbage_disk_size: 0 } }
+n1@1 → n2 ClientResponse id=0x03 status Status { leader: 1, term: 1, match_index: {1: 2, 2: 2, 3: 1}, commit_index: 2, apply_index: 2, storage: Status { name: "memory", keys: 4, size: 41, total_disk_size: 0, live_disk_size: 0, garbage_disk_size: 0 } }
+n2@1 → c2 ClientResponse id=0x03 status Status { leader: 1, term: 1, match_index: {1: 2, 2: 2, 3: 1}, commit_index: 2, apply_index: 2, storage: Status { name: "memory", keys: 4, size: 41, total_disk_size: 0, live_disk_size: 0, garbage_disk_size: 0 } }
 c2@1 status ⇒ Status {
  leader: 1,
  term: 1,
- last_index: {
+ match_index: {
  1: 2,
  2: 2,
  3: 1,

src/raft/testscripts/node/request_status_single

@@ -16,11 +16,11 @@ status request=true 1
 stabilize
 ---
 c1@1 → n1 ClientRequest id=0x02 status
-n1@1 → c1 ClientResponse id=0x02 status Status { leader: 1, term: 1, last_index: {1: 2}, commit_index: 2, apply_index: 2, storage: Status { name: "memory", keys: 4, size: 41, total_disk_size: 0, live_disk_size: 0, garbage_disk_size: 0 } }
+n1@1 → c1 ClientResponse id=0x02 status Status { leader: 1, term: 1, match_index: {1: 2}, commit_index: 2, apply_index: 2, storage: Status { name: "memory", keys: 4, size: 41, total_disk_size: 0, live_disk_size: 0, garbage_disk_size: 0 } }
 c1@1 status ⇒ Status {
  leader: 1,
  term: 1,
- last_index: {
+ match_index: {
  1: 2,
  },
  commit_index: 2,

tests/e2e/client.rs

@@ -126,7 +126,7 @@ fn status() -> Result<()> {
  raft: raft::Status {
  leader: 1,
  term: 1,
- last_index: [(1, 27)].into(),
+ match_index: [(1, 27)].into(),
  commit_index: 27,
  apply_index: 27,
  storage: storage::engine::Status {