Added a error log when learner is not sync with etcd leader.

Signed-off-by: ishan16696 <[email protected]>

server/etcdserver/server.go

@@ -1491,7 +1491,7 @@ func (s *EtcdServer) promoteMember(ctx context.Context, id uint64) ([]*membershi
 
 func (s *EtcdServer) mayPromoteMember(id types.ID) error {
 	lg := s.Logger()
-	err := s.isLearnerReady(uint64(id))
+	err := s.isLearnerReady(lg, uint64(id))
 	if err != nil {
 		return err
 	}
@@ -1515,7 +1515,7 @@ func (s *EtcdServer) mayPromoteMember(id types.ID) error {
 // check whether the learner catches up with leader or not.
 // Note: it will return nil if member is not found in cluster or if member is not learner.
 // These two conditions will be checked before toApply phase later.
-func (s *EtcdServer) isLearnerReady(id uint64) error {
+func (s *EtcdServer) isLearnerReady(lg *zap.Logger, id uint64) error {
 	if err := s.waitAppliedIndex(); err != nil {
 		return err
 	}
@@ -1546,8 +1546,14 @@ func (s *EtcdServer) isLearnerReady(id uint64) error {
 	}
 
 	leaderMatch := rs.Progress[leaderID].Match
+	learnerReadyPercent := float64(learnerMatch) / float64(leaderMatch)
+
 	// the learner's Match not caught up with leader yet
-	if float64(learnerMatch) < float64(leaderMatch)*readyPercent {
+	if learnerReadyPercent < readyPercent {
+		lg.Error(
+			"rejecting promote learner: learner is not ready",
+			zap.Float64("learner-ready-percent", learnerReadyPercent),
+		)
 		return errors.ErrLearnerNotReady
 	}