id: fix the id allocator is not monotonic

server/id/id.go

@@ -55,12 +55,11 @@ func (alloc *AllocatorImpl) Alloc() (uint64, error) {
 	defer alloc.mu.Unlock()
 
 	if alloc.base == alloc.end {
-		end, err := alloc.generate()
+		err := alloc.Generate()
 		if err != nil {
 			return 0, err
 		}
 
-		alloc.end = end
 		alloc.base = alloc.end - allocStep
 	}
 
@@ -69,11 +68,12 @@ func (alloc *AllocatorImpl) Alloc() (uint64, error) {
 	return alloc.base, nil
 }
 
-func (alloc *AllocatorImpl) generate() (uint64, error) {
+// Generate synchronizes and generates id range.
+func (alloc *AllocatorImpl) Generate() error {
 	key := alloc.getAllocIDPath()
 	value, err := etcdutil.GetValue(alloc.client, key)
 	if err != nil {
-		return 0, err
+		return err
 	}
 
 	var (
@@ -88,7 +88,7 @@ func (alloc *AllocatorImpl) generate() (uint64, error) {
 		// update the key
 		end, err = typeutil.BytesToUint64(value)
 		if err != nil {
-			return 0, err
+			return err
 		}
 
 		cmp = clientv3.Compare(clientv3.Value(key), "=", string(value))
@@ -101,15 +101,16 @@ func (alloc *AllocatorImpl) generate() (uint64, error) {
 	t := txn.If(append([]clientv3.Cmp{cmp}, clientv3.Compare(clientv3.Value(leaderPath), "=", alloc.member))...)
 	resp, err := t.Then(clientv3.OpPut(key, string(value))).Commit()
 	if err != nil {
-		return 0, errs.ErrEtcdTxn.Wrap(err).GenWithStackByArgs()
+		return errs.ErrEtcdTxn.Wrap(err).GenWithStackByArgs()
 	}
 	if !resp.Succeeded {
-		return 0, errs.ErrEtcdTxn.FastGenByArgs()
+		return errs.ErrEtcdTxn.FastGenByArgs()
 	}
 
 	log.Info("idAllocator allocates a new id", zap.Uint64("alloc-id", end))
 	idGauge.WithLabelValues("idalloc").Set(float64(end))
-	return end, nil
+	alloc.end = end
+	return nil
 }
 
 func (alloc *AllocatorImpl) getAllocIDPath() string {

server/server.go

@@ -1223,6 +1223,10 @@ func (s *Server) campaignLeader() {
 		log.Error("failed to load persistOptions from etcd", errs.ZapError(err))
 		return
 	}
+	if err := s.idAllocator.Generate(); err != nil {
+		log.Error("failed to sync id from etcd", errs.ZapError(err))
+		return
+	}
 	s.member.EnableLeader()
 
 	CheckPDVersion(s.persistOptions)

tests/server/id/id_test.go

@@ -119,3 +119,48 @@ func (s *testAllocIDSuite) TestCommand(c *C) {
 		last = resp.GetId()
 	}
 }
+
+func (s *testAllocIDSuite) TestMonotonicID(c *C) {
+	var err error
+	cluster, err := tests.NewTestCluster(s.ctx, 2)
+	defer cluster.Destroy()
+	c.Assert(err, IsNil)
+
+	err = cluster.RunInitialServers()
+	c.Assert(err, IsNil)
+	cluster.WaitLeader()
+
+	leaderServer := cluster.GetServer(cluster.GetLeader())
+	var last1 uint64
+	for i := uint64(0); i < 10; i++ {
+		id, err := leaderServer.GetAllocator().Alloc()
+		c.Assert(err, IsNil)
+		c.Assert(id, Greater, last1)
+		last1 = id
+	}
+	err = cluster.ResignLeader()
+	c.Assert(err, IsNil)
+	cluster.WaitLeader()
+	leaderServer = cluster.GetServer(cluster.GetLeader())
+	var last2 uint64
+	for i := uint64(0); i < 10; i++ {
+		id, err := leaderServer.GetAllocator().Alloc()
+		c.Assert(err, IsNil)
+		c.Assert(id, Greater, last2)
+		last2 = id
+	}
+	err = cluster.ResignLeader()
+	c.Assert(err, IsNil)
+	cluster.WaitLeader()
+	leaderServer = cluster.GetServer(cluster.GetLeader())
+	id, err := leaderServer.GetAllocator().Alloc()
+	c.Assert(err, IsNil)
+	c.Assert(id, Greater, last2)
+	var last3 uint64
+	for i := uint64(0); i < 1000; i++ {
+		id, err := leaderServer.GetAllocator().Alloc()
+		c.Assert(err, IsNil)
+		c.Assert(id, Greater, last3)
+		last3 = id
+	}
+}