etcdserver: adjust election ticks on restart

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

etcdserver/server.go

@@ -539,6 +539,33 @@ func NewServer(cfg ServerConfig) (srv *EtcdServer, err error) {
 	}
 	srv.r.transport = tr
 
+	srv.goAttach(func() {
+		clusterN := len(cl.Members())
+
+		// single-node fresh start, or single-node recovers from snapshot
+		if clusterN == 1 {
+			ticks := cfg.ElectionTicks - 1
+			plog.Infof("%s as single-node; fast-forwarding %d ticks (election ticks %d) with %d found member(s)", srv.ID(), ticks, cfg.ElectionTicks, clusterN)
+			srv.advanceRaftTicks(ticks)
+			return
+		}
+
+		select {
+		case <-tr.InitialPeerNotify():
+			// multi-node received peer connection reports
+			// adjust ticks, in case slow leader message receive
+			ticks := cfg.ElectionTicks - 2
+			plog.Infof("%s initialzed peer connection; fast-forwarding %d ticks (election ticks %d) with %d found member(s)", srv.ID(), ticks, cfg.ElectionTicks, len(cl.Members()))
+			srv.advanceRaftTicks(ticks)
+
+		case <-time.After(rafthttp.ConnReadTimeout):
+			// advancing ticks would have no effect when:
+			// 1. all connections failed, or
+			// 2. no active peers, or
+			// 3. restarted single-node with no snapshot
+			plog.Infof("%s waited %s but no active peer found (or restarted 1-node cluster); currently, %d member(s)", srv.ID(), rafthttp.ConnReadTimeout, len(cl.Members()))
+		}
+	})
 	return srv, nil
 }