Merge pull request #165 from pav-kv/maybe-update

tracker: clean-up Match, Next and MaybeUpdate

confchange/confchange.go

@@ -259,8 +259,8 @@ func (c Changer) initProgress(cfg *tracker.Config, trk tracker.ProgressMap, id u
 		// at all (and will thus likely need a snapshot), though the app may
 		// have applied a snapshot out of band before adding the replica (thus
 		// making the first index the better choice).
-		Next:      c.LastIndex,
 		Match:     0,
+		Next:      max(c.LastIndex, 1), // invariant: Match < Next
 		Inflights: tracker.NewInflights(c.Tracker.MaxInflight, c.Tracker.MaxInflightBytes),
 		IsLearner: isLearner,
 		// When a node is first added, we should mark it as recently active.

confchange/testdata/joint_autoleave.txt

@@ -5,14 +5,14 @@ simple
 v1
 ----
 voters=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 
 # Autoleave is reflected in the config.
 enter-joint autoleave=true
 v2 v3
 ----
 voters=(1 2 3)&&(1) autoleave
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1
 3: StateProbe match=0 next=1
 
@@ -24,6 +24,6 @@ config is already joint
 leave-joint
 ----
 voters=(1 2 3)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1
 3: StateProbe match=0 next=1

confchange/testdata/joint_idempotency.txt

@@ -5,19 +5,19 @@ simple
 v1
 ----
 voters=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 
 enter-joint
 r1 r2 r9 v2 v3 v4 v2 v3 v4 l2 l2 r4 r4 l1 l1
 ----
 voters=(3)&&(1) learners=(2) learners_next=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1 learner
 3: StateProbe match=0 next=1
 
 leave-joint
 ----
 voters=(3) learners=(1 2)
-1: StateProbe match=0 next=0 learner
+1: StateProbe match=0 next=1 learner
 2: StateProbe match=0 next=1 learner
 3: StateProbe match=0 next=1

confchange/testdata/joint_learners_next.txt

@@ -8,17 +8,17 @@ simple
 v1
 ----
 voters=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 
 enter-joint
 v2 l1
 ----
 voters=(2)&&(1) learners_next=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1
 
 leave-joint
 ----
 voters=(2) learners=(1)
-1: StateProbe match=0 next=0 learner
+1: StateProbe match=0 next=1 learner
 2: StateProbe match=0 next=1

confchange/testdata/simple_idempotency.txt

@@ -2,33 +2,33 @@ simple
 v1
 ----
 voters=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 
 simple
 v1
 ----
 voters=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 
 simple
 v2
 ----
 voters=(1 2)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=2
 
 simple
 l1
 ----
 voters=(2) learners=(1)
-1: StateProbe match=0 next=0 learner
+1: StateProbe match=0 next=1 learner
 2: StateProbe match=0 next=2
 
 simple
 l1
 ----
 voters=(2) learners=(1)
-1: StateProbe match=0 next=0 learner
+1: StateProbe match=0 next=1 learner
 2: StateProbe match=0 next=2
 
 simple

confchange/testdata/simple_promote_demote.txt

@@ -4,20 +4,20 @@ simple
 v1
 ----
 voters=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 
 simple
 v2
 ----
 voters=(1 2)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1
 
 simple
 v3
 ----
 voters=(1 2 3)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1
 3: StateProbe match=0 next=2
 
@@ -27,7 +27,7 @@ simple
 l1 v1
 ----
 voters=(1 2 3)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1
 3: StateProbe match=0 next=2
 
@@ -36,7 +36,7 @@ simple
 l2
 ----
 voters=(1 3) learners=(2)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1 learner
 3: StateProbe match=0 next=2
 
@@ -46,7 +46,7 @@ simple
 v2 l2
 ----
 voters=(1 3) learners=(2)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1 learner
 3: StateProbe match=0 next=2
 
@@ -55,6 +55,6 @@ simple
 v2
 ----
 voters=(1 2 3)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1
 3: StateProbe match=0 next=2

confchange/testdata/update.txt

@@ -6,18 +6,18 @@ simple
 v1
 ----
 voters=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 
 simple
 v2 u1
 ----
 voters=(1 2)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1
 
 simple
 u1 u2 u3 u1 u2 u3
 ----
 voters=(1 2)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1
 2: StateProbe match=0 next=1

confchange/testdata/zero.txt

@@ -3,4 +3,4 @@ simple
 v1 r0 v0 l0
 ----
 voters=(1)
-1: StateProbe match=0 next=0
+1: StateProbe match=0 next=1

raft.go

@@ -1902,9 +1902,6 @@ func (r *raft) restore(s pb.Snapshot) bool {
 
 	assertConfStatesEquivalent(r.logger, cs, r.switchToConfig(cfg, trk))
 
-	pr := r.trk.Progress[r.id]
-	pr.MaybeUpdate(pr.Next - 1) // TODO(tbg): this is untested and likely unneeded
-
 	last := r.raftLog.lastEntryID()
 	r.logger.Infof("%x [commit: %d, lastindex: %d, lastterm: %d] restored snapshot [index: %d, term: %d]",
 		r.id, r.raftLog.committed, last.index, last.term, id.index, id.term)

tracker/progress.go

@@ -28,7 +28,15 @@ import (
 // strewn around `*raft.raft`. Additionally, some fields are only used when in a
 // certain State. All of this isn't ideal.
 type Progress struct {
-	Match, Next uint64
+	// Match is the index up to which the follower's log is known to match the
+	// leader's.
+	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.
+	//
+	// Invariant: 0 <= Match < Next.
+	Next uint64
+
 	// State defines how the leader should interact with the follower.
 	//
 	// When in StateProbe, leader sends at most one replication message
@@ -166,14 +174,13 @@ func (pr *Progress) UpdateOnEntriesSend(entries int, bytes uint64) {
 // 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.
 func (pr *Progress) MaybeUpdate(n uint64) bool {
-	var updated bool
-	if pr.Match < n {
-		pr.Match = n
-		updated = true
-		pr.MsgAppFlowPaused = false
+	if n <= pr.Match {
+		return false
 	}
-	pr.Next = max(pr.Next, n+1)
-	return updated
+	pr.Match = n
+	pr.Next = max(pr.Next, n+1) // invariant: Match < Next
+	pr.MsgAppFlowPaused = false
+	return true
 }
 
 // MaybeDecrTo adjusts the Progress to the receipt of a MsgApp rejection. The
@@ -208,7 +215,6 @@ func (pr *Progress) MaybeDecrTo(rejected, matchHint uint64) bool {
 		return false
 	}
 
-	// Next index shall always be larger than match index.
 	pr.Next = max(min(rejected, matchHint+1), pr.Match+1)
 	pr.MsgAppFlowPaused = false
 	return true