raftLog: compact applied entries only

compact MUST happen on entries that have been applied, or
1. it may screw up the log by setting wrong commitIndex
2. discard unapplied entries

raft/log.go

@@ -152,8 +152,8 @@ func (l *raftLog) maybeCommit(maxIndex, term int64) bool {
 // and not greater than the index of the last entry.
 // the number of entries after compaction will be returned.
 func (l *raftLog) compact(i int64) int64 {
-	if l.isOutOfBounds(i) {
-		panic(fmt.Sprintf("compact %d out of bounds [%d:%d]", i, l.offset, l.lastIndex()))
+	if l.isOutOfAppliedBounds(i) {
+		panic(fmt.Sprintf("compact %d out of bounds [%d:%d]", i, l.offset, l.applied))
 	}
 	l.ents = l.slice(i, l.lastIndex()+1)
 	l.unstable = max(i+1, l.unstable)
@@ -208,6 +208,13 @@ func (l *raftLog) isOutOfBounds(i int64) bool {
 	return false
 }
 
+func (l *raftLog) isOutOfAppliedBounds(i int64) bool {
+	if i < l.offset || i > l.applied {
+		return true
+	}
+	return false
+}
+
 func min(a, b int64) int64 {
 	if a > b {
 		return b

raft/log_test.go

@@ -76,11 +76,14 @@ func TestAppend(t *testing.T) {
 func TestCompactionSideEffects(t *testing.T) {
 	var i int64
 	lastIndex := int64(1000)
+	lastTerm := lastIndex
 	raftLog := newLog()
 
 	for i = 0; i < lastIndex; i++ {
 		raftLog.append(int64(i), pb.Entry{Term: int64(i + 1), Index: int64(i + 1)})
 	}
+	raftLog.maybeCommit(lastIndex, lastTerm)
+	raftLog.resetNextEnts()
 
 	raftLog.compact(500)
 
@@ -149,16 +152,18 @@ func TestUnstableEnts(t *testing.T) {
 //TestCompaction ensures that the number of log entreis is correct after compactions.
 func TestCompaction(t *testing.T) {
 	tests := []struct {
-		app     int
+		applied   int64
+		lastIndex int64
 		compact   []int64
 		wleft     []int
 		wallow    bool
 	}{
 		// out of upper bound
-		{1000, []int64{1001}, []int{-1}, false},
-		{1000, []int64{300, 500, 800, 900}, []int{701, 501, 201, 101}, true},
+		{1000, 1000, []int64{1001}, []int{-1}, false},
+		{1000, 1000, []int64{300, 500, 800, 900}, []int{701, 501, 201, 101}, true},
 		// out of lower bound
-		{1000, []int64{300, 299}, []int{701, -1}, false},
+		{1000, 1000, []int64{300, 299}, []int{701, -1}, false},
+		{0, 1000, []int64{1}, []int{-1}, false},
 	}
 
 	for i, tt := range tests {
@@ -172,9 +177,11 @@ func TestCompaction(t *testing.T) {
 			}()
 
 			raftLog := newLog()
-			for i := 0; i < tt.app; i++ {
+			for i := int64(0); i < tt.lastIndex; i++ {
 				raftLog.append(int64(i), pb.Entry{})
 			}
+			raftLog.maybeCommit(tt.applied, 0)
+			raftLog.resetNextEnts()
 
 			for j := 0; j < len(tt.compact); j++ {
 				raftLog.compact(tt.compact[j])