From be44bcf073635b7e2312cc284626961d57b94f2b Mon Sep 17 00:00:00 2001
From: Ryan Leung <rleungx@gmail.com>
Date: Mon, 28 Dec 2020 13:04:44 +0800
Subject: [PATCH] cherry pick #3305 to release-2.1

Signed-off-by: Ryan Leung <rleungx@gmail.com>
---
 server/id.go      | 24 ++++++++++++++++--------
 server/id_test.go | 45 +++++++++++++++++++++++++++++++++++++++++++++
 server/leader.go  |  5 +++++
 3 files changed, 66 insertions(+), 8 deletions(-)

diff --git a/server/id.go b/server/id.go
index 047d96a637b8..0b0d8b3ab65c 100644
--- a/server/id.go
+++ b/server/id.go
@@ -39,8 +39,7 @@ func (alloc *idAllocator) Alloc() (uint64, error) {
 	defer alloc.mu.Unlock()
 
 	if alloc.base == alloc.end {
-		end, err := alloc.generate()
-		if err != nil {
+		if err := alloc.generateLocked(); err != nil {
 			return 0, err
 		}
 
@@ -53,11 +52,19 @@ func (alloc *idAllocator) Alloc() (uint64, error) {
 	return alloc.base, nil
 }
 
-func (alloc *idAllocator) generate() (uint64, error) {
+// Generate synchronizes and generates id range.
+func (alloc *idAllocator) Generate() error {
+	alloc.mu.Lock()
+	defer alloc.mu.Unlock()
+
+	return alloc.generateLocked()
+}
+
+func (alloc *idAllocator) generateLocked() error {
 	key := alloc.s.getAllocIDPath()
 	value, err := getValue(alloc.s.client, key)
 	if err != nil {
-		return 0, err
+		return err
 	}
 
 	var (
@@ -72,7 +79,7 @@ func (alloc *idAllocator) generate() (uint64, error) {
 		// update the key
 		end, err = bytesToUint64(value)
 		if err != nil {
-			return 0, err
+			return err
 		}
 
 		cmp = clientv3.Compare(clientv3.Value(key), "=", string(value))
@@ -82,13 +89,14 @@ func (alloc *idAllocator) generate() (uint64, error) {
 	value = uint64ToBytes(end)
 	resp, err := alloc.s.leaderTxn(cmp).Then(clientv3.OpPut(key, string(value))).Commit()
 	if err != nil {
-		return 0, err
+		return err
 	}
 	if !resp.Succeeded {
-		return 0, errors.New("generate id failed, we may not leader")
+		return errors.New("generate id failed, we may not leader")
 	}
 
 	log.Info("idAllocator allocates a new id", zap.Uint64("alloc-id", end))
 	metadataGauge.WithLabelValues("idalloc").Set(float64(end))
-	return end, nil
+	alloc.end = end
+	return nil
 }
diff --git a/server/id_test.go b/server/id_test.go
index 4590da04cea1..12414f708656 100644
--- a/server/id_test.go
+++ b/server/id_test.go
@@ -95,3 +95,48 @@ 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
+	}
+}
diff --git a/server/leader.go b/server/leader.go
index fcb70a24d7f1..5cdd75673ebc 100644
--- a/server/leader.go
+++ b/server/leader.go
@@ -274,6 +274,11 @@ func (s *Server) campaignLeader() error {
 		physical: zeroTime,
 	})
 
+	log.Info("sync id from etcd")
+	if err = s.idAlloc.Generate(); err != nil {
+		return err
+	}
+
 	s.enableLeader()
 	defer s.disableLeader()