From c5efcdd16f528a46ee5877d9e25511d55f688beb Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Mon, 16 Aug 2021 17:07:53 +0800
Subject: [PATCH 01/18] support storing placement policy in meta

Signed-off-by: ailinkid <314806019@qq.com>
---
 ddl/placement/policy.go  | 32 +++++++++++++
 errno/errcode.go         |  2 +
 errno/errname.go         | 12 +++--
 infoschema/builder.go    |  9 ++++
 infoschema/infoschema.go | 38 +++++++++++++++
 meta/meta.go             | 99 ++++++++++++++++++++++++++++++++++++++++
 meta/meta_test.go        | 99 ++++++++++++++++++++++++++++++++++++++++
 7 files changed, 286 insertions(+), 5 deletions(-)
 create mode 100644 ddl/placement/policy.go

diff --git a/ddl/placement/policy.go b/ddl/placement/policy.go
new file mode 100644
index 0000000000000..7eeaf0458edba
--- /dev/null
+++ b/ddl/placement/policy.go
@@ -0,0 +1,32 @@
+// Copyright 2021 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package placement
+
+import "github.com/pingcap/parser/model"
+
+// Policy is the struct to store the placement policy.
+type Policy struct {
+	ID                  int64       `json:"id"`
+	Name                model.CIStr `json:"name"`
+	PrimaryRegion       string      `json:"primary_region"`
+	Regions             string      `json:"regions"`
+	Leaders             int64       `json:"leaders"`
+	Followers           int64       `json:"followers"`
+	Voters              int64       `json:"voters"`
+	Schedule            string      `json:"schedule"`
+	Constraints         Constraints `json:"constraints"`
+	LeaderConstraints   Constraints `json:"leader_constraints"`
+	FollowerConstraints Constraints `json:"follower_constraints"`
+	VoterConstraints    Constraints `json:"voter_constraints"`
+}
diff --git a/errno/errcode.go b/errno/errcode.go
index 15b78afbe8d59..ff9e011cb03cf 100644
--- a/errno/errcode.go
+++ b/errno/errcode.go
@@ -1047,6 +1047,8 @@ const (
 	ErrDDLReorgElementNotExist            = 8235
 	ErrPlacementPolicyCheck               = 8236
 	ErrInvalidAttributesSpec              = 8237
+	ErrPlacementPolicyExists              = 8238
+	ErrPlacementPolicyNotExists           = 8239
 
 	// TiKV/PD/TiFlash errors.
 	ErrPDServerTimeout           = 9001
diff --git a/errno/errname.go b/errno/errname.go
index be242bbcb14b7..9862d88a9b599 100644
--- a/errno/errname.go
+++ b/errno/errname.go
@@ -1049,11 +1049,13 @@ var MySQLErrName = map[uint16]*mysql.ErrMessage{
 	ErrPartitionStatsMissing: mysql.Message("Build table: %s global-level stats failed due to missing partition-level stats", nil),
 	ErrNotSupportedWithSem:   mysql.Message("Feature '%s' is not supported when security enhanced mode is enabled", nil),
 
-	ErrInvalidPlacementSpec:   mysql.Message("Invalid placement policy '%s': %s", nil),
-	ErrPlacementPolicyCheck:   mysql.Message("Placement policy didn't meet the constraint, reason: %s", nil),
-	ErrMultiStatementDisabled: mysql.Message("client has multi-statement capability disabled. Run SET GLOBAL tidb_multi_statement_mode='ON' after you understand the security risk", nil),
-	ErrAsOf:                   mysql.Message("invalid as of timestamp: %s", nil),
-	ErrInvalidAttributesSpec:  mysql.Message("Invalid attributes '%s': %s", nil),
+	ErrInvalidPlacementSpec:     mysql.Message("Invalid placement policy '%s': %s", nil),
+	ErrPlacementPolicyCheck:     mysql.Message("Placement policy didn't meet the constraint, reason: %s", nil),
+	ErrMultiStatementDisabled:   mysql.Message("client has multi-statement capability disabled. Run SET GLOBAL tidb_multi_statement_mode='ON' after you understand the security risk", nil),
+	ErrAsOf:                     mysql.Message("invalid as of timestamp: %s", nil),
+	ErrInvalidAttributesSpec:    mysql.Message("Invalid attributes '%s': %s", nil),
+	ErrPlacementPolicyExists:    mysql.Message("Can't create placement policy '%-.192s'; policy exists", nil),
+	ErrPlacementPolicyNotExists: mysql.Message("Unknown placement policy '%-.192s'", nil),
 
 	// TiKV/PD errors.
 	ErrPDServerTimeout:           mysql.Message("PD server timeout", nil),
diff --git a/infoschema/builder.go b/infoschema/builder.go
index 88e8b71add319..f35f48a28e44f 100644
--- a/infoschema/builder.go
+++ b/infoschema/builder.go
@@ -484,6 +484,7 @@ func (b *Builder) InitWithOldInfoSchema(oldSchema InfoSchema) *Builder {
 	b.is.schemaMetaVersion = oldIS.schemaMetaVersion
 	b.copySchemasMap(oldIS)
 	b.copyBundlesMap(oldIS)
+	b.copyPoliciesMap(oldIS)
 	copy(b.is.sortedTablesBuckets, oldIS.sortedTablesBuckets)
 	return b
 }
@@ -501,6 +502,13 @@ func (b *Builder) copyBundlesMap(oldIS *infoSchema) {
 	}
 }
 
+func (b *Builder) copyPoliciesMap(oldIS *infoSchema) {
+	is := b.is
+	for _, v := range oldIS.PlacementPolicies() {
+		is.SetPolicy(v)
+	}
+}
+
 // copySchemaTables creates a new schemaTables instance when a table in the database has changed.
 // It also does modifications on the new one because old schemaTables must be read-only.
 // Note: please make sure the dbName is in lowercase.
@@ -588,6 +596,7 @@ func NewBuilder(store kv.Storage) *Builder {
 		store: store,
 		is: &infoSchema{
 			schemaMap:           map[string]*schemaTables{},
+			policyMap:           map[string]*placement.Policy{},
 			ruleBundleMap:       map[string]*placement.Bundle{},
 			sortedTablesBuckets: make([]sortedTables, bucketCount),
 		},
diff --git a/infoschema/infoschema.go b/infoschema/infoschema.go
index 41b5b2c2f6e7c..a6f810cebfc73 100644
--- a/infoschema/infoschema.go
+++ b/infoschema/infoschema.go
@@ -93,6 +93,10 @@ type infoSchema struct {
 	ruleBundleMutex sync.RWMutex
 	ruleBundleMap   map[string]*placement.Bundle
 
+	// policyMap stores all placement policies.
+	policyMutex sync.RWMutex
+	policyMap   map[string]*placement.Policy
+
 	schemaMap map[string]*schemaTables
 
 	// sortedTablesBuckets is a slice of sortedTables, a table's bucket index is (tableID % bucketCount).
@@ -106,6 +110,7 @@ type infoSchema struct {
 func MockInfoSchema(tbList []*model.TableInfo) InfoSchema {
 	result := &infoSchema{}
 	result.schemaMap = make(map[string]*schemaTables)
+	result.policyMap = make(map[string]*placement.Policy)
 	result.ruleBundleMap = make(map[string]*placement.Bundle)
 	result.sortedTablesBuckets = make([]sortedTables, bucketCount)
 	dbInfo := &model.DBInfo{ID: 0, Name: model.NewCIStr("test"), Tables: tbList}
@@ -130,6 +135,7 @@ func MockInfoSchema(tbList []*model.TableInfo) InfoSchema {
 func MockInfoSchemaWithSchemaVer(tbList []*model.TableInfo, schemaVer int64) InfoSchema {
 	result := &infoSchema{}
 	result.schemaMap = make(map[string]*schemaTables)
+	result.policyMap = make(map[string]*placement.Policy)
 	result.ruleBundleMap = make(map[string]*placement.Bundle)
 	result.sortedTablesBuckets = make([]sortedTables, bucketCount)
 	dbInfo := &model.DBInfo{ID: 0, Name: model.NewCIStr("test"), Tables: tbList}
@@ -346,6 +352,38 @@ func HasAutoIncrementColumn(tbInfo *model.TableInfo) (bool, string) {
 	return false, ""
 }
 
+// PolicyByName is used to find the policy.
+func (is *infoSchema) PolicyByName(name string) (*placement.Policy, bool) {
+	is.policyMutex.RLock()
+	defer is.policyMutex.RUnlock()
+	t, r := is.policyMap[name]
+	return t, r
+}
+
+// SetPolicy is used to set the policy.
+func (is *infoSchema) SetPolicy(policy *placement.Policy) {
+	is.policyMutex.Lock()
+	defer is.policyMutex.Unlock()
+	is.policyMap[policy.Name.L] = policy
+}
+
+// DeletePolicy is used to delete the policy.
+func (is *infoSchema) DeletePolicy(name string) {
+	is.policyMutex.Lock()
+	defer is.policyMutex.Unlock()
+	delete(is.policyMap, name)
+}
+
+func (is *infoSchema) PlacementPolicies() []*placement.Policy {
+	is.policyMutex.RLock()
+	defer is.policyMutex.RUnlock()
+	policies := make([]*placement.Policy, 0, len(is.policyMap))
+	for _, policy := range is.policyMap {
+		policies = append(policies, policy)
+	}
+	return policies
+}
+
 func (is *infoSchema) BundleByName(name string) (*placement.Bundle, bool) {
 	is.ruleBundleMutex.RLock()
 	defer is.ruleBundleMutex.RUnlock()
diff --git a/meta/meta.go b/meta/meta.go
index e52bc41290b68..170b95116fcde 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -17,6 +17,7 @@ import (
 	"encoding/binary"
 	"encoding/json"
 	"fmt"
+	"github.com/pingcap/tidb/ddl/placement"
 	"math"
 	"sort"
 	"strconv"
@@ -39,6 +40,7 @@ import (
 
 var (
 	globalIDMutex sync.Mutex
+	policyIDMutex sync.Mutex
 )
 
 // Meta structure:
@@ -69,6 +71,9 @@ var (
 	mRandomIDPrefix   = "TARID"
 	mBootstrapKey     = []byte("BootstrapKey")
 	mSchemaDiffPrefix = "Diff"
+	mPolicies         = []byte("Policies")
+	mPolicyPrefix     = "Policy"
+	mPolicyGlobalID   = []byte("PolicyGlobalID")
 )
 
 var (
@@ -76,6 +81,10 @@ var (
 	ErrDBExists = dbterror.ClassMeta.NewStd(mysql.ErrDBCreateExists)
 	// ErrDBNotExists is the error for db not exists.
 	ErrDBNotExists = dbterror.ClassMeta.NewStd(mysql.ErrBadDB)
+	// ErrPolicyExists is the error for policy exists.
+	ErrPolicyExists = dbterror.ClassMeta.NewStd(errno.ErrPlacementPolicyExists)
+	// ErrPolicyNotExists is the error for policy not exists.
+	ErrPolicyNotExists = dbterror.ClassMeta.NewStd(errno.ErrPlacementPolicyNotExists)
 	// ErrTableExists is the error for table exists.
 	ErrTableExists = dbterror.ClassMeta.NewStd(mysql.ErrTableExists)
 	// ErrTableNotExists is the error for table not exists.
@@ -144,6 +153,21 @@ func (m *Meta) GetGlobalID() (int64, error) {
 	return m.txn.GetInt64(mNextGlobalIDKey)
 }
 
+func (m *Meta) GenPolicyID() (int64, error) {
+	policyIDMutex.Lock()
+	defer policyIDMutex.Unlock()
+
+	return m.txn.Inc(mPolicyGlobalID, 1)
+}
+
+func (m *Meta) GetPolicyID() (int64, error) {
+	return m.txn.GetInt64(mPolicyGlobalID)
+}
+
+func (m *Meta) policyKey(policyID int64) []byte {
+	return []byte(fmt.Sprintf("%s:%d", mPolicyPrefix, policyID))
+}
+
 func (m *Meta) dbKey(dbID int64) []byte {
 	return []byte(fmt.Sprintf("%s:%d", mDBPrefix, dbID))
 }
@@ -267,6 +291,22 @@ func (m *Meta) GenSchemaVersion() (int64, error) {
 	return m.txn.Inc(mSchemaVersionKey, 1)
 }
 
+func (m *Meta) checkPolicyExists(policyKey []byte) error {
+	v, err := m.txn.HGet(mPolicies, policyKey)
+	if err == nil && v == nil {
+		err = ErrPolicyNotExists.GenWithStack("policy doesn't exist")
+	}
+	return errors.Trace(err)
+}
+
+func (m *Meta) checkPolicyNotExists(policyKey []byte) error {
+	v, err := m.txn.HGet(mPolicies, policyKey)
+	if err == nil && v != nil {
+		err = ErrPolicyExists.GenWithStack("policy already exists")
+	}
+	return errors.Trace(err)
+}
+
 func (m *Meta) checkDBExists(dbKey []byte) error {
 	v, err := m.txn.HGet(mDBs, dbKey)
 	if err == nil && v == nil {
@@ -299,6 +339,33 @@ func (m *Meta) checkTableNotExists(dbKey []byte, tableKey []byte) error {
 	return errors.Trace(err)
 }
 
+func (m *Meta) CreatePolicy(policy *placement.Policy) error {
+	policyKey := m.policyKey(policy.ID)
+
+	if err := m.checkPolicyNotExists(policyKey); err != nil {
+		return errors.Trace(err)
+	}
+	data, err := json.Marshal(policy)
+	if err != nil {
+		return errors.Trace(err)
+	}
+	return m.txn.HSet(mPolicies, policyKey, data)
+}
+
+func (m *Meta) UpdatePolicy(policy *placement.Policy) error {
+	policyKey := m.policyKey(policy.ID)
+
+	if err := m.checkPolicyExists(policyKey); err != nil {
+		return errors.Trace(err)
+	}
+
+	data, err := json.Marshal(policy)
+	if err != nil {
+		return errors.Trace(err)
+	}
+	return m.txn.HSet(mPolicies, policyKey, data)
+}
+
 // CreateDatabase creates a database with db info.
 func (m *Meta) CreateDatabase(dbInfo *model.DBInfo) error {
 	dbKey := m.dbKey(dbInfo.ID)
@@ -551,6 +618,38 @@ func (m *Meta) GetDatabase(dbID int64) (*model.DBInfo, error) {
 	return dbInfo, errors.Trace(err)
 }
 
+// ListPolicies shows all policies.
+func (m *Meta) ListPolicies() ([]*placement.Policy, error) {
+	res, err := m.txn.HGetAll(mPolicies)
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
+
+	policies := make([]*placement.Policy, 0, len(res))
+	for _, r := range res {
+		policy := &placement.Policy{}
+		err = json.Unmarshal(r.Value, policy)
+		if err != nil {
+			return nil, errors.Trace(err)
+		}
+		policies = append(policies, policy)
+	}
+	return policies, nil
+}
+
+// GetPolicy gets the database value with ID.
+func (m *Meta) GetPolicy(policyID int64) (*placement.Policy, error) {
+	policyKey := m.policyKey(policyID)
+	value, err := m.txn.HGet(mPolicies, policyKey)
+	if err != nil || value == nil {
+		return nil, errors.Trace(err)
+	}
+
+	policy := &placement.Policy{}
+	err = json.Unmarshal(value, policy)
+	return policy, errors.Trace(err)
+}
+
 // GetTable gets the table value in database with tableID.
 func (m *Meta) GetTable(dbID int64, tableID int64) (*model.TableInfo, error) {
 	// Check if db exists.
diff --git a/meta/meta_test.go b/meta/meta_test.go
index 341b15981188e..0be8e86941471 100644
--- a/meta/meta_test.go
+++ b/meta/meta_test.go
@@ -16,6 +16,7 @@ package meta_test
 import (
 	"context"
 	"fmt"
+	"github.com/pingcap/tidb/ddl/placement"
 	"math"
 	"strconv"
 	"sync"
@@ -31,6 +32,104 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestPlacementPolicy(t *testing.T) {
+	t.Parallel()
+
+	store, err := mockstore.NewMockStore()
+	require.NoError(t, err)
+
+	defer func() {
+		err := store.Close()
+		require.NoError(t, err)
+	}()
+
+	txn, err := store.Begin()
+	require.NoError(t, err)
+
+	// test the independent policy ID allocation.
+	m := meta.NewMeta(txn)
+	id, err := m.GenPolicyID()
+	require.NoError(t, err)
+	require.Equal(t, int64(1), id)
+
+	id, err = m.GetPolicyID()
+	require.NoError(t, err)
+	require.Equal(t, int64(1), id)
+
+	id, err = m.GenPolicyID()
+	require.NoError(t, err)
+	require.Equal(t, int64(2), id)
+
+	// test the meta storage of placemnt policy.
+	policy := &placement.Policy{
+		ID:            1,
+		Name:          model.NewCIStr("aa"),
+		PrimaryRegion: "my primary",
+		Regions:       "my regions",
+		Leaders:       1,
+		Followers:     2,
+		Voters:        3,
+		Schedule:      "even",
+		Constraints: placement.Constraints{
+			{
+				Key:    "disk",
+				Op:     placement.In,
+				Values: []string{"ssd"},
+			},
+		},
+		LeaderConstraints: placement.Constraints{
+			{
+				Key:    "zone",
+				Op:     placement.In,
+				Values: []string{"shanghai"},
+			},
+		},
+	}
+	err = m.CreatePolicy(policy)
+	require.NoError(t, err)
+
+	err = m.CreatePolicy(policy)
+	require.NotNil(t, err)
+	require.True(t, meta.ErrPolicyExists.Equal(err))
+
+	val, err := m.GetPolicy(1)
+	require.NoError(t, err)
+	require.Equal(t, policy, val)
+
+	// mock updating the placement policy.
+	policy.Name = model.NewCIStr("bb")
+	policy.LeaderConstraints = placement.Constraints{
+		{
+			Key:    "zone",
+			Op:     placement.In,
+			Values: []string{"nanjing"},
+		}}
+	err = m.UpdatePolicy(policy)
+	require.NoError(t, err)
+
+	val, err = m.GetPolicy(1)
+	require.NoError(t, err)
+	require.Equal(t, policy, val)
+
+	ps, err := m.ListPolicies()
+	require.NoError(t, err)
+	require.Equal(t, []*placement.Policy{policy}, ps)
+
+	err = txn.Commit(context.Background())
+	require.NoError(t, err)
+
+	// fetch the stored value after committing.
+	txn, err = store.Begin()
+	require.NoError(t, err)
+
+	m = meta.NewMeta(txn)
+	val, err = m.GetPolicy(1)
+	require.NoError(t, err)
+	require.Equal(t, policy, val)
+	err = txn.Commit(context.Background())
+	require.NoError(t, err)
+}
+
 func TestMeta(t *testing.T) {
 	t.Parallel()
 

From f982dcbc6ff8574c3aff0d1bc2c47dace61fa615 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Mon, 16 Aug 2021 17:15:28 +0800
Subject: [PATCH 02/18] solve the import problem

Signed-off-by: ailinkid <314806019@qq.com>
---
 meta/meta.go      | 2 +-
 meta/meta_test.go | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/meta/meta.go b/meta/meta.go
index 170b95116fcde..40f7499a5cb64 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -17,7 +17,6 @@ import (
 	"encoding/binary"
 	"encoding/json"
 	"fmt"
-	"github.com/pingcap/tidb/ddl/placement"
 	"math"
 	"sort"
 	"strconv"
@@ -29,6 +28,7 @@ import (
 	"github.com/pingcap/kvproto/pkg/kvrpcpb"
 	"github.com/pingcap/parser/model"
 	"github.com/pingcap/parser/mysql"
+	"github.com/pingcap/tidb/ddl/placement"
 	"github.com/pingcap/tidb/errno"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/metrics"
diff --git a/meta/meta_test.go b/meta/meta_test.go
index 0be8e86941471..d19b22a6b462d 100644
--- a/meta/meta_test.go
+++ b/meta/meta_test.go
@@ -16,7 +16,6 @@ package meta_test
 import (
 	"context"
 	"fmt"
-	"github.com/pingcap/tidb/ddl/placement"
 	"math"
 	"strconv"
 	"sync"
@@ -25,6 +24,7 @@ import (
 
 	"github.com/pingcap/errors"
 	"github.com/pingcap/parser/model"
+	"github.com/pingcap/tidb/ddl/placement"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/meta"
 	"github.com/pingcap/tidb/store/mockstore"

From fa317e4fabbb275776c71bf902018e95b00e8b21 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Tue, 17 Aug 2021 10:59:15 +0800
Subject: [PATCH 03/18] address commnet

Signed-off-by: ailinkid <314806019@qq.com>
---
 ddl/placement/policy.go  | 11 +++++++----
 infoschema/infoschema.go |  7 -------
 meta/meta_test.go        | 40 ++++++++++++----------------------------
 3 files changed, 19 insertions(+), 39 deletions(-)

diff --git a/ddl/placement/policy.go b/ddl/placement/policy.go
index 7eeaf0458edba..573c530e7418e 100644
--- a/ddl/placement/policy.go
+++ b/ddl/placement/policy.go
@@ -15,8 +15,11 @@ package placement
 
 import "github.com/pingcap/parser/model"
 
+const DefaultPolicyMagicVer uint32 = 0
+
 // Policy is the struct to store the placement policy.
 type Policy struct {
+	MagicVer            uint32      `json:"magic_ver"`
 	ID                  int64       `json:"id"`
 	Name                model.CIStr `json:"name"`
 	PrimaryRegion       string      `json:"primary_region"`
@@ -25,8 +28,8 @@ type Policy struct {
 	Followers           int64       `json:"followers"`
 	Voters              int64       `json:"voters"`
 	Schedule            string      `json:"schedule"`
-	Constraints         Constraints `json:"constraints"`
-	LeaderConstraints   Constraints `json:"leader_constraints"`
-	FollowerConstraints Constraints `json:"follower_constraints"`
-	VoterConstraints    Constraints `json:"voter_constraints"`
+	Constraints         string      `json:"constraints"`
+	LeaderConstraints   string      `json:"leader_constraints"`
+	FollowerConstraints string      `json:"follower_constraints"`
+	VoterConstraints    string      `json:"voter_constraints"`
 }
diff --git a/infoschema/infoschema.go b/infoschema/infoschema.go
index 6e2688305a130..794961229173f 100644
--- a/infoschema/infoschema.go
+++ b/infoschema/infoschema.go
@@ -368,13 +368,6 @@ func (is *infoSchema) SetPolicy(policy *placement.Policy) {
 	is.policyMap[policy.Name.L] = policy
 }
 
-// DeletePolicy is used to delete the policy.
-func (is *infoSchema) DeletePolicy(name string) {
-	is.policyMutex.Lock()
-	defer is.policyMutex.Unlock()
-	delete(is.policyMap, name)
-}
-
 func (is *infoSchema) PlacementPolicies() []*placement.Policy {
 	is.policyMutex.RLock()
 	defer is.policyMutex.RUnlock()
diff --git a/meta/meta_test.go b/meta/meta_test.go
index df7819fd54d7e..fc9d50413a11d 100644
--- a/meta/meta_test.go
+++ b/meta/meta_test.go
@@ -63,28 +63,17 @@ func TestPlacementPolicy(t *testing.T) {
 
 	// test the meta storage of placemnt policy.
 	policy := &placement.Policy{
-		ID:            1,
-		Name:          model.NewCIStr("aa"),
-		PrimaryRegion: "my primary",
-		Regions:       "my regions",
-		Leaders:       1,
-		Followers:     2,
-		Voters:        3,
-		Schedule:      "even",
-		Constraints: placement.Constraints{
-			{
-				Key:    "disk",
-				Op:     placement.In,
-				Values: []string{"ssd"},
-			},
-		},
-		LeaderConstraints: placement.Constraints{
-			{
-				Key:    "zone",
-				Op:     placement.In,
-				Values: []string{"shanghai"},
-			},
-		},
+		MagicVer:          placement.DefaultPolicyMagicVer,
+		ID:                1,
+		Name:              model.NewCIStr("aa"),
+		PrimaryRegion:     "my primary",
+		Regions:           "my regions",
+		Leaders:           1,
+		Followers:         2,
+		Voters:            3,
+		Schedule:          "even",
+		Constraints:       "+disk=ssd",
+		LeaderConstraints: "+zone=shanghai",
 	}
 	err = m.CreatePolicy(policy)
 	require.NoError(t, err)
@@ -99,12 +88,7 @@ func TestPlacementPolicy(t *testing.T) {
 
 	// mock updating the placement policy.
 	policy.Name = model.NewCIStr("bb")
-	policy.LeaderConstraints = placement.Constraints{
-		{
-			Key:    "zone",
-			Op:     placement.In,
-			Values: []string{"nanjing"},
-		}}
+	policy.LeaderConstraints = "+zone=nanjing"
 	err = m.UpdatePolicy(policy)
 	require.NoError(t, err)
 

From 91f1d793da2f322ae23b0550e2d180d8d1fa2061 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Tue, 17 Aug 2021 14:54:26 +0800
Subject: [PATCH 04/18] add magic number for policy

Signed-off-by: ailinkid <314806019@qq.com>
---
 ddl/placement/policy.go |  3 ---
 meta/meta.go            | 54 ++++++++++++++++++++++++++++++++++++++---
 meta/meta_test.go       |  1 -
 3 files changed, 51 insertions(+), 7 deletions(-)

diff --git a/ddl/placement/policy.go b/ddl/placement/policy.go
index 573c530e7418e..2c5104212e32b 100644
--- a/ddl/placement/policy.go
+++ b/ddl/placement/policy.go
@@ -15,11 +15,8 @@ package placement
 
 import "github.com/pingcap/parser/model"
 
-const DefaultPolicyMagicVer uint32 = 0
-
 // Policy is the struct to store the placement policy.
 type Policy struct {
-	MagicVer            uint32      `json:"magic_ver"`
 	ID                  int64       `json:"id"`
 	Name                model.CIStr `json:"name"`
 	PrimaryRegion       string      `json:"primary_region"`
diff --git a/meta/meta.go b/meta/meta.go
index bbcfd297c23fc..afc6d8db5ae8b 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -75,6 +75,21 @@ var (
 	mPolicies         = []byte("Policies")
 	mPolicyPrefix     = "Policy"
 	mPolicyGlobalID   = []byte("PolicyGlobalID")
+	mPolicyMagicByte  = CurrentMagicByteVer
+)
+
+const (
+	CurrentMagicByteVer byte = 0x00
+	// PolicyMagicByte handler
+	// 0x00 - 0x3F: Json Handler
+	// 0x40 - 0x7F: Reserved
+	// 0x80 - 0xBF: Reserved
+	// 0xC0 - 0xFF: Reserved
+
+	// type means how to handle the serialized data.
+	typeJson    int = 1
+	typeUnknown int = 2
+	// todo: customized handler.
 )
 
 var (
@@ -350,7 +365,7 @@ func (m *Meta) CreatePolicy(policy *placement.Policy) error {
 	if err != nil {
 		return errors.Trace(err)
 	}
-	return m.txn.HSet(mPolicies, policyKey, data)
+	return m.txn.HSet(mPolicies, policyKey, attachMagicByte(data))
 }
 
 func (m *Meta) UpdatePolicy(policy *placement.Policy) error {
@@ -364,7 +379,7 @@ func (m *Meta) UpdatePolicy(policy *placement.Policy) error {
 	if err != nil {
 		return errors.Trace(err)
 	}
-	return m.txn.HSet(mPolicies, policyKey, data)
+	return m.txn.HSet(mPolicies, policyKey, attachMagicByte(data))
 }
 
 // CreateDatabase creates a database with db info.
@@ -628,8 +643,12 @@ func (m *Meta) ListPolicies() ([]*placement.Policy, error) {
 
 	policies := make([]*placement.Policy, 0, len(res))
 	for _, r := range res {
+		value, err := detachMagicByte(r.Value)
+		if err != nil {
+			return nil, errors.Trace(err)
+		}
 		policy := &placement.Policy{}
-		err = json.Unmarshal(r.Value, policy)
+		err = json.Unmarshal(value, policy)
 		if err != nil {
 			return nil, errors.Trace(err)
 		}
@@ -645,12 +664,41 @@ func (m *Meta) GetPolicy(policyID int64) (*placement.Policy, error) {
 	if err != nil || value == nil {
 		return nil, errors.Trace(err)
 	}
+	value, err = detachMagicByte(value)
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
 
 	policy := &placement.Policy{}
 	err = json.Unmarshal(value, policy)
 	return policy, errors.Trace(err)
 }
 
+func attachMagicByte(data []byte) []byte {
+	dataWithHeader := make([]byte, 0, len(data)+1)
+	dataWithHeader = append(dataWithHeader, mPolicyMagicByte)
+	dataWithHeader = append(dataWithHeader, data...)
+	return dataWithHeader
+}
+
+func detachMagicByte(value []byte) ([]byte, error) {
+	magic, data := value[:1], value[1:]
+	switch whichMagicType(magic[0]) {
+	case typeJson:
+		return data, nil
+	default:
+		//
+		return nil, errors.New("unknown magic type handling module")
+	}
+}
+
+func whichMagicType(b byte) int {
+	if b < 0x3F {
+		return typeJson
+	}
+	return typeUnknown
+}
+
 // GetTable gets the table value in database with tableID.
 func (m *Meta) GetTable(dbID int64, tableID int64) (*model.TableInfo, error) {
 	// Check if db exists.
diff --git a/meta/meta_test.go b/meta/meta_test.go
index fc9d50413a11d..e5e754d76592e 100644
--- a/meta/meta_test.go
+++ b/meta/meta_test.go
@@ -63,7 +63,6 @@ func TestPlacementPolicy(t *testing.T) {
 
 	// test the meta storage of placemnt policy.
 	policy := &placement.Policy{
-		MagicVer:          placement.DefaultPolicyMagicVer,
 		ID:                1,
 		Name:              model.NewCIStr("aa"),
 		PrimaryRegion:     "my primary",

From 643499de065e42465ea65b099abbfbc301d75469 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Tue, 17 Aug 2021 14:57:08 +0800
Subject: [PATCH 05/18] .

Signed-off-by: ailinkid <314806019@qq.com>
---
 meta/meta.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meta/meta.go b/meta/meta.go
index afc6d8db5ae8b..bdd13f4411f78 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -693,7 +693,7 @@ func detachMagicByte(value []byte) ([]byte, error) {
 }
 
 func whichMagicType(b byte) int {
-	if b < 0x3F {
+	if b <= 0x3F {
 		return typeJson
 	}
 	return typeUnknown

From bd193699cdc66f865644c5bb910d09a739bca098 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Wed, 18 Aug 2021 13:56:16 +0800
Subject: [PATCH 06/18] address comment

Signed-off-by: ailinkid <314806019@qq.com>
---
 meta/meta.go | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/meta/meta.go b/meta/meta.go
index bdd13f4411f78..9cf60cbde7f19 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -675,10 +675,10 @@ func (m *Meta) GetPolicy(policyID int64) (*placement.Policy, error) {
 }
 
 func attachMagicByte(data []byte) []byte {
-	dataWithHeader := make([]byte, 0, len(data)+1)
-	dataWithHeader = append(dataWithHeader, mPolicyMagicByte)
-	dataWithHeader = append(dataWithHeader, data...)
-	return dataWithHeader
+	data = append(data, 0)
+	copy(data[1:], data)
+	data[0] = mPolicyMagicByte
+	return data
 }
 
 func detachMagicByte(value []byte) ([]byte, error) {

From 3896af73df3ea96514c1e5455ec0e341186e968a Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Wed, 18 Aug 2021 14:09:32 +0800
Subject: [PATCH 07/18] address comment

Signed-off-by: ailinkid <314806019@qq.com>
---
 meta/meta.go | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/meta/meta.go b/meta/meta.go
index 9cf60cbde7f19..ef3208f325f38 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -79,6 +79,7 @@ var (
 )
 
 const (
+	// CurrentMagicByteVer is the current magic byte version.
 	CurrentMagicByteVer byte = 0x00
 	// PolicyMagicByte handler
 	// 0x00 - 0x3F: Json Handler
@@ -87,7 +88,7 @@ const (
 	// 0xC0 - 0xFF: Reserved
 
 	// type means how to handle the serialized data.
-	typeJson    int = 1
+	typeJSON    int = 1
 	typeUnknown int = 2
 	// todo: customized handler.
 )
@@ -169,6 +170,7 @@ func (m *Meta) GetGlobalID() (int64, error) {
 	return m.txn.GetInt64(mNextGlobalIDKey)
 }
 
+// GenPolicyID generates the next policy global id.
 func (m *Meta) GenPolicyID() (int64, error) {
 	policyIDMutex.Lock()
 	defer policyIDMutex.Unlock()
@@ -176,6 +178,7 @@ func (m *Meta) GenPolicyID() (int64, error) {
 	return m.txn.Inc(mPolicyGlobalID, 1)
 }
 
+// GetPolicyID gets current policy global id.
 func (m *Meta) GetPolicyID() (int64, error) {
 	return m.txn.GetInt64(mPolicyGlobalID)
 }
@@ -355,6 +358,7 @@ func (m *Meta) checkTableNotExists(dbKey []byte, tableKey []byte) error {
 	return errors.Trace(err)
 }
 
+// CreatePolicy creates a policy.
 func (m *Meta) CreatePolicy(policy *placement.Policy) error {
 	policyKey := m.policyKey(policy.ID)
 
@@ -368,6 +372,7 @@ func (m *Meta) CreatePolicy(policy *placement.Policy) error {
 	return m.txn.HSet(mPolicies, policyKey, attachMagicByte(data))
 }
 
+// UpdatePolicy updates a policy.
 func (m *Meta) UpdatePolicy(policy *placement.Policy) error {
 	policyKey := m.policyKey(policy.ID)
 
@@ -684,7 +689,7 @@ func attachMagicByte(data []byte) []byte {
 func detachMagicByte(value []byte) ([]byte, error) {
 	magic, data := value[:1], value[1:]
 	switch whichMagicType(magic[0]) {
-	case typeJson:
+	case typeJSON:
 		return data, nil
 	default:
 		//

From 70aab7ae53bb484e62b7615772f08b7a78e456f2 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Wed, 18 Aug 2021 14:17:48 +0800
Subject: [PATCH 08/18] address comment

Signed-off-by: ailinkid <314806019@qq.com>
---
 meta/meta.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meta/meta.go b/meta/meta.go
index ef3208f325f38..1e00979c2aefb 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -699,7 +699,7 @@ func detachMagicByte(value []byte) ([]byte, error) {
 
 func whichMagicType(b byte) int {
 	if b <= 0x3F {
-		return typeJson
+		return typeJSON
 	}
 	return typeUnknown
 }

From 2e64f19eb380520953cbfbe01a718c3522a9cb5a Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Wed, 18 Aug 2021 15:15:44 +0800
Subject: [PATCH 09/18] error

Signed-off-by: ailinkid <314806019@qq.com>
---
 errors.toml | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/errors.toml b/errors.toml
index cd2bdd0b89abc..a6143d74bcd2a 100644
--- a/errors.toml
+++ b/errors.toml
@@ -1061,6 +1061,16 @@ error = '''
 DDL reorg element does not exist
 '''
 
+["meta:8238"]
+error = '''
+Can't create placement policy '%-.192s'; policy exists
+'''
+
+["meta:8239"]
+error = '''
+Unknown placement policy '%-.192s'
+'''
+
 ["planner:1044"]
 error = '''
 Access denied for user '%-.48s'@'%-.64s' to database '%-.192s'

From 9c931ebdd5009309ff0bef68c9ab35903c461ebd Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Wed, 18 Aug 2021 16:16:33 +0800
Subject: [PATCH 10/18] .

Signed-off-by: ailinkid <314806019@qq.com>
---
 ddl/placement/policy.go | 1 +
 1 file changed, 1 insertion(+)

diff --git a/ddl/placement/policy.go b/ddl/placement/policy.go
index 2c5104212e32b..51849542dc78a 100644
--- a/ddl/placement/policy.go
+++ b/ddl/placement/policy.go
@@ -8,6 +8,7 @@
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 

From bcb66cb1f844e38508675fc04edc56d47f84047a Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Thu, 19 Aug 2021 11:48:55 +0800
Subject: [PATCH 11/18] address comment

Signed-off-by: ailinkid <314806019@qq.com>
---
 infoschema/builder.go    | 4 +++-
 infoschema/infoschema.go | 7 -------
 meta/meta.go             | 2 +-
 3 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/infoschema/builder.go b/infoschema/builder.go
index 90b6f7d3e3b22..db70f2b2b1fcb 100644
--- a/infoschema/builder.go
+++ b/infoschema/builder.go
@@ -505,8 +505,10 @@ func (b *Builder) copyBundlesMap(oldIS *infoSchema) {
 
 func (b *Builder) copyPoliciesMap(oldIS *infoSchema) {
 	is := b.is
+	is.policyMutex.Lock()
+	defer is.policyMutex.Unlock()
 	for _, v := range oldIS.PlacementPolicies() {
-		is.SetPolicy(v)
+		is.policyMap[v.Name.L] = v
 	}
 }
 
diff --git a/infoschema/infoschema.go b/infoschema/infoschema.go
index 794961229173f..78fc4f40663e8 100644
--- a/infoschema/infoschema.go
+++ b/infoschema/infoschema.go
@@ -361,13 +361,6 @@ func (is *infoSchema) PolicyByName(name string) (*placement.Policy, bool) {
 	return t, r
 }
 
-// SetPolicy is used to set the policy.
-func (is *infoSchema) SetPolicy(policy *placement.Policy) {
-	is.policyMutex.Lock()
-	defer is.policyMutex.Unlock()
-	is.policyMap[policy.Name.L] = policy
-}
-
 func (is *infoSchema) PlacementPolicies() []*placement.Policy {
 	is.policyMutex.RLock()
 	defer is.policyMutex.RUnlock()
diff --git a/meta/meta.go b/meta/meta.go
index 1e00979c2aefb..6677fbdfbaf2b 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -79,7 +79,7 @@ var (
 )
 
 const (
-	// CurrentMagicByteVer is the current magic byte version.
+	// CurrentMagicByteVer is the current magic byte version, used for future meta compatibility.
 	CurrentMagicByteVer byte = 0x00
 	// PolicyMagicByte handler
 	// 0x00 - 0x3F: Json Handler

From ffb8605c08870392af880048005187d5883d4771 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Fri, 20 Aug 2021 17:08:42 +0800
Subject: [PATCH 12/18] address comment

Signed-off-by: ailinkid <314806019@qq.com>
---
 ddl/placement/policy.go         | 33 -------------------------------
 infoschema/builder.go           |  3 ++-
 infoschema/infoschema.go        | 13 ++++++------
 meta/meta.go                    | 33 ++++++++++++++++---------------
 util/placement_policy/policy.go | 35 +++++++++++++++++++++++++++++++++
 5 files changed, 61 insertions(+), 56 deletions(-)
 delete mode 100644 ddl/placement/policy.go
 create mode 100644 util/placement_policy/policy.go

diff --git a/ddl/placement/policy.go b/ddl/placement/policy.go
deleted file mode 100644
index 51849542dc78a..0000000000000
--- a/ddl/placement/policy.go
+++ /dev/null
@@ -1,33 +0,0 @@
-// Copyright 2021 PingCAP, Inc.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package placement
-
-import "github.com/pingcap/parser/model"
-
-// Policy is the struct to store the placement policy.
-type Policy struct {
-	ID                  int64       `json:"id"`
-	Name                model.CIStr `json:"name"`
-	PrimaryRegion       string      `json:"primary_region"`
-	Regions             string      `json:"regions"`
-	Leaders             int64       `json:"leaders"`
-	Followers           int64       `json:"followers"`
-	Voters              int64       `json:"voters"`
-	Schedule            string      `json:"schedule"`
-	Constraints         string      `json:"constraints"`
-	LeaderConstraints   string      `json:"leader_constraints"`
-	FollowerConstraints string      `json:"follower_constraints"`
-	VoterConstraints    string      `json:"voter_constraints"`
-}
diff --git a/infoschema/builder.go b/infoschema/builder.go
index db70f2b2b1fcb..f4fb99032e2ed 100644
--- a/infoschema/builder.go
+++ b/infoschema/builder.go
@@ -26,6 +26,7 @@ import (
 	"github.com/pingcap/parser/model"
 	"github.com/pingcap/tidb/config"
 	"github.com/pingcap/tidb/ddl/placement"
+	"github.com/pingcap/tidb/util/placement_policy"
 	"github.com/pingcap/tidb/domain/infosync"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/meta"
@@ -599,7 +600,7 @@ func NewBuilder(store kv.Storage) *Builder {
 		store: store,
 		is: &infoSchema{
 			schemaMap:           map[string]*schemaTables{},
-			policyMap:           map[string]*placement.Policy{},
+			policyMap:           map[string]*placement_policy.PolicyInfo{},
 			ruleBundleMap:       map[string]*placement.Bundle{},
 			sortedTablesBuckets: make([]sortedTables, bucketCount),
 		},
diff --git a/infoschema/infoschema.go b/infoschema/infoschema.go
index 78fc4f40663e8..98959db30bcc9 100644
--- a/infoschema/infoschema.go
+++ b/infoschema/infoschema.go
@@ -25,6 +25,7 @@ import (
 	"github.com/pingcap/tidb/meta/autoid"
 	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/util"
+	"github.com/pingcap/tidb/util/placement_policy"
 )
 
 // InfoSchema is the interface used to retrieve the schema information.
@@ -96,7 +97,7 @@ type infoSchema struct {
 
 	// policyMap stores all placement policies.
 	policyMutex sync.RWMutex
-	policyMap   map[string]*placement.Policy
+	policyMap   map[string]*placement_policy.PolicyInfo
 
 	schemaMap map[string]*schemaTables
 
@@ -111,7 +112,7 @@ type infoSchema struct {
 func MockInfoSchema(tbList []*model.TableInfo) InfoSchema {
 	result := &infoSchema{}
 	result.schemaMap = make(map[string]*schemaTables)
-	result.policyMap = make(map[string]*placement.Policy)
+	result.policyMap = make(map[string]*placement_policy.PolicyInfo)
 	result.ruleBundleMap = make(map[string]*placement.Bundle)
 	result.sortedTablesBuckets = make([]sortedTables, bucketCount)
 	dbInfo := &model.DBInfo{ID: 0, Name: model.NewCIStr("test"), Tables: tbList}
@@ -136,7 +137,7 @@ func MockInfoSchema(tbList []*model.TableInfo) InfoSchema {
 func MockInfoSchemaWithSchemaVer(tbList []*model.TableInfo, schemaVer int64) InfoSchema {
 	result := &infoSchema{}
 	result.schemaMap = make(map[string]*schemaTables)
-	result.policyMap = make(map[string]*placement.Policy)
+	result.policyMap = make(map[string]*placement_policy.PolicyInfo)
 	result.ruleBundleMap = make(map[string]*placement.Bundle)
 	result.sortedTablesBuckets = make([]sortedTables, bucketCount)
 	dbInfo := &model.DBInfo{ID: 0, Name: model.NewCIStr("test"), Tables: tbList}
@@ -354,17 +355,17 @@ func HasAutoIncrementColumn(tbInfo *model.TableInfo) (bool, string) {
 }
 
 // PolicyByName is used to find the policy.
-func (is *infoSchema) PolicyByName(name string) (*placement.Policy, bool) {
+func (is *infoSchema) PolicyByName(name string) (*placement_policy.PolicyInfo, bool) {
 	is.policyMutex.RLock()
 	defer is.policyMutex.RUnlock()
 	t, r := is.policyMap[name]
 	return t, r
 }
 
-func (is *infoSchema) PlacementPolicies() []*placement.Policy {
+func (is *infoSchema) PlacementPolicies() []*placement_policy.PolicyInfo {
 	is.policyMutex.RLock()
 	defer is.policyMutex.RUnlock()
-	policies := make([]*placement.Policy, 0, len(is.policyMap))
+	policies := make([]*placement_policy.PolicyInfo, 0, len(is.policyMap))
 	for _, policy := range is.policyMap {
 		policies = append(policies, policy)
 	}
diff --git a/meta/meta.go b/meta/meta.go
index 6677fbdfbaf2b..51a300a5bc684 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -29,13 +29,13 @@ import (
 	"github.com/pingcap/kvproto/pkg/kvrpcpb"
 	"github.com/pingcap/parser/model"
 	"github.com/pingcap/parser/mysql"
-	"github.com/pingcap/tidb/ddl/placement"
 	"github.com/pingcap/tidb/errno"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/metrics"
 	"github.com/pingcap/tidb/structure"
 	"github.com/pingcap/tidb/util/dbterror"
 	"github.com/pingcap/tidb/util/logutil"
+	placement "github.com/pingcap/tidb/util/placement_policy"
 	"go.uber.org/zap"
 )
 
@@ -170,14 +170,6 @@ func (m *Meta) GetGlobalID() (int64, error) {
 	return m.txn.GetInt64(mNextGlobalIDKey)
 }
 
-// GenPolicyID generates the next policy global id.
-func (m *Meta) GenPolicyID() (int64, error) {
-	policyIDMutex.Lock()
-	defer policyIDMutex.Unlock()
-
-	return m.txn.Inc(mPolicyGlobalID, 1)
-}
-
 // GetPolicyID gets current policy global id.
 func (m *Meta) GetPolicyID() (int64, error) {
 	return m.txn.GetInt64(mPolicyGlobalID)
@@ -359,7 +351,16 @@ func (m *Meta) checkTableNotExists(dbKey []byte, tableKey []byte) error {
 }
 
 // CreatePolicy creates a policy.
-func (m *Meta) CreatePolicy(policy *placement.Policy) error {
+func (m *Meta) CreatePolicy(policy *placement.PolicyInfo) error {
+	// Autofill the policy ID.
+	policyIDMutex.Lock()
+	genID, err := m.txn.Inc(mPolicyGlobalID, 1)
+	if err != nil {
+		return errors.Trace(err)
+	}
+	policyIDMutex.Unlock()
+
+	policy.ID = genID
 	policyKey := m.policyKey(policy.ID)
 
 	if err := m.checkPolicyNotExists(policyKey); err != nil {
@@ -373,7 +374,7 @@ func (m *Meta) CreatePolicy(policy *placement.Policy) error {
 }
 
 // UpdatePolicy updates a policy.
-func (m *Meta) UpdatePolicy(policy *placement.Policy) error {
+func (m *Meta) UpdatePolicy(policy *placement.PolicyInfo) error {
 	policyKey := m.policyKey(policy.ID)
 
 	if err := m.checkPolicyExists(policyKey); err != nil {
@@ -640,19 +641,19 @@ func (m *Meta) GetDatabase(dbID int64) (*model.DBInfo, error) {
 }
 
 // ListPolicies shows all policies.
-func (m *Meta) ListPolicies() ([]*placement.Policy, error) {
+func (m *Meta) ListPolicies() ([]*placement.PolicyInfo, error) {
 	res, err := m.txn.HGetAll(mPolicies)
 	if err != nil {
 		return nil, errors.Trace(err)
 	}
 
-	policies := make([]*placement.Policy, 0, len(res))
+	policies := make([]*placement.PolicyInfo, 0, len(res))
 	for _, r := range res {
 		value, err := detachMagicByte(r.Value)
 		if err != nil {
 			return nil, errors.Trace(err)
 		}
-		policy := &placement.Policy{}
+		policy := &placement.PolicyInfo{}
 		err = json.Unmarshal(value, policy)
 		if err != nil {
 			return nil, errors.Trace(err)
@@ -663,7 +664,7 @@ func (m *Meta) ListPolicies() ([]*placement.Policy, error) {
 }
 
 // GetPolicy gets the database value with ID.
-func (m *Meta) GetPolicy(policyID int64) (*placement.Policy, error) {
+func (m *Meta) GetPolicy(policyID int64) (*placement.PolicyInfo, error) {
 	policyKey := m.policyKey(policyID)
 	value, err := m.txn.HGet(mPolicies, policyKey)
 	if err != nil || value == nil {
@@ -674,7 +675,7 @@ func (m *Meta) GetPolicy(policyID int64) (*placement.Policy, error) {
 		return nil, errors.Trace(err)
 	}
 
-	policy := &placement.Policy{}
+	policy := &placement.PolicyInfo{}
 	err = json.Unmarshal(value, policy)
 	return policy, errors.Trace(err)
 }
diff --git a/util/placement_policy/policy.go b/util/placement_policy/policy.go
new file mode 100644
index 0000000000000..f86323c63a1da
--- /dev/null
+++ b/util/placement_policy/policy.go
@@ -0,0 +1,35 @@
+// Copyright 2021 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package placement_policy
+
+import (
+	"github.com/pingcap/parser/model"
+)
+
+// PolicyInfo is the struct to store the placement_policy policy.
+type PolicyInfo struct {
+	ID                  int64             `json:"id"`
+	Name                model.CIStr       `json:"name"`
+	PrimaryRegion       string            `json:"primary_region"`
+	Regions             string            `json:"regions"`
+	Learners            uint64            `json:"learners"`
+	Followers           uint64            `json:"followers"`
+	Voters              uint64            `json:"voters"`
+	Schedule            string            `json:"schedule"`
+	Constraints         string            `json:"constraints"`
+	LearnerConstraints  string            `json:"learner_constraints"`
+	FollowerConstraints string            `json:"follower_constraints"`
+	VoterConstraints    string            `json:"voter_constraints"`
+	State               model.SchemaState `json:"state"`
+}

From 3be7de87dbcc203c2692fbd18f1b5987b2ccf3f2 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Fri, 20 Aug 2021 17:17:16 +0800
Subject: [PATCH 13/18] address comment

Signed-off-by: ailinkid <314806019@qq.com>
---
 util/placement_policy/policy.go | 1 +
 1 file changed, 1 insertion(+)

diff --git a/util/placement_policy/policy.go b/util/placement_policy/policy.go
index f86323c63a1da..84a5ab73f3d22 100644
--- a/util/placement_policy/policy.go
+++ b/util/placement_policy/policy.go
@@ -8,6 +8,7 @@
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 

From dae2b36136445d833ae7be1e3737d695f66cdfb6 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Fri, 20 Aug 2021 17:20:50 +0800
Subject: [PATCH 14/18] address comment

Signed-off-by: ailinkid <314806019@qq.com>
---
 infoschema/builder.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/infoschema/builder.go b/infoschema/builder.go
index f4fb99032e2ed..e95b3f3e25cee 100644
--- a/infoschema/builder.go
+++ b/infoschema/builder.go
@@ -26,7 +26,6 @@ import (
 	"github.com/pingcap/parser/model"
 	"github.com/pingcap/tidb/config"
 	"github.com/pingcap/tidb/ddl/placement"
-	"github.com/pingcap/tidb/util/placement_policy"
 	"github.com/pingcap/tidb/domain/infosync"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/meta"
@@ -34,6 +33,7 @@ import (
 	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/table/tables"
 	"github.com/pingcap/tidb/util/domainutil"
+	"github.com/pingcap/tidb/util/placement_policy"
 )
 
 // Builder builds a new InfoSchema.

From 2c7e5a3e9193c74049563147d09afcabb477087a Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Fri, 20 Aug 2021 17:36:50 +0800
Subject: [PATCH 15/18] address comment

Signed-off-by: ailinkid <314806019@qq.com>
---
 infoschema/builder.go                              |  4 ++--
 infoschema/infoschema.go                           | 14 +++++++-------
 meta/meta.go                                       |  2 +-
 .../policy.go                                      |  4 ++--
 4 files changed, 12 insertions(+), 12 deletions(-)
 rename util/{placement_policy => placementpolicy}/policy.go (94%)

diff --git a/infoschema/builder.go b/infoschema/builder.go
index e95b3f3e25cee..d86ef74e3ddce 100644
--- a/infoschema/builder.go
+++ b/infoschema/builder.go
@@ -33,7 +33,7 @@ import (
 	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/table/tables"
 	"github.com/pingcap/tidb/util/domainutil"
-	"github.com/pingcap/tidb/util/placement_policy"
+	"github.com/pingcap/tidb/util/placementpolicy"
 )
 
 // Builder builds a new InfoSchema.
@@ -600,7 +600,7 @@ func NewBuilder(store kv.Storage) *Builder {
 		store: store,
 		is: &infoSchema{
 			schemaMap:           map[string]*schemaTables{},
-			policyMap:           map[string]*placement_policy.PolicyInfo{},
+			policyMap:           map[string]*placementpolicy.PolicyInfo{},
 			ruleBundleMap:       map[string]*placement.Bundle{},
 			sortedTablesBuckets: make([]sortedTables, bucketCount),
 		},
diff --git a/infoschema/infoschema.go b/infoschema/infoschema.go
index 98959db30bcc9..b13d0ede1fdbe 100644
--- a/infoschema/infoschema.go
+++ b/infoschema/infoschema.go
@@ -25,7 +25,7 @@ import (
 	"github.com/pingcap/tidb/meta/autoid"
 	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/util"
-	"github.com/pingcap/tidb/util/placement_policy"
+	"github.com/pingcap/tidb/util/placementpolicy"
 )
 
 // InfoSchema is the interface used to retrieve the schema information.
@@ -97,7 +97,7 @@ type infoSchema struct {
 
 	// policyMap stores all placement policies.
 	policyMutex sync.RWMutex
-	policyMap   map[string]*placement_policy.PolicyInfo
+	policyMap   map[string]*placementpolicy.PolicyInfo
 
 	schemaMap map[string]*schemaTables
 
@@ -112,7 +112,7 @@ type infoSchema struct {
 func MockInfoSchema(tbList []*model.TableInfo) InfoSchema {
 	result := &infoSchema{}
 	result.schemaMap = make(map[string]*schemaTables)
-	result.policyMap = make(map[string]*placement_policy.PolicyInfo)
+	result.policyMap = make(map[string]*placementpolicy.PolicyInfo)
 	result.ruleBundleMap = make(map[string]*placement.Bundle)
 	result.sortedTablesBuckets = make([]sortedTables, bucketCount)
 	dbInfo := &model.DBInfo{ID: 0, Name: model.NewCIStr("test"), Tables: tbList}
@@ -137,7 +137,7 @@ func MockInfoSchema(tbList []*model.TableInfo) InfoSchema {
 func MockInfoSchemaWithSchemaVer(tbList []*model.TableInfo, schemaVer int64) InfoSchema {
 	result := &infoSchema{}
 	result.schemaMap = make(map[string]*schemaTables)
-	result.policyMap = make(map[string]*placement_policy.PolicyInfo)
+	result.policyMap = make(map[string]*placementpolicy.PolicyInfo)
 	result.ruleBundleMap = make(map[string]*placement.Bundle)
 	result.sortedTablesBuckets = make([]sortedTables, bucketCount)
 	dbInfo := &model.DBInfo{ID: 0, Name: model.NewCIStr("test"), Tables: tbList}
@@ -355,17 +355,17 @@ func HasAutoIncrementColumn(tbInfo *model.TableInfo) (bool, string) {
 }
 
 // PolicyByName is used to find the policy.
-func (is *infoSchema) PolicyByName(name string) (*placement_policy.PolicyInfo, bool) {
+func (is *infoSchema) PolicyByName(name string) (*placementpolicy.PolicyInfo, bool) {
 	is.policyMutex.RLock()
 	defer is.policyMutex.RUnlock()
 	t, r := is.policyMap[name]
 	return t, r
 }
 
-func (is *infoSchema) PlacementPolicies() []*placement_policy.PolicyInfo {
+func (is *infoSchema) PlacementPolicies() []*placementpolicy.PolicyInfo {
 	is.policyMutex.RLock()
 	defer is.policyMutex.RUnlock()
-	policies := make([]*placement_policy.PolicyInfo, 0, len(is.policyMap))
+	policies := make([]*placementpolicy.PolicyInfo, 0, len(is.policyMap))
 	for _, policy := range is.policyMap {
 		policies = append(policies, policy)
 	}
diff --git a/meta/meta.go b/meta/meta.go
index 51a300a5bc684..34bd78f4fca11 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -35,7 +35,7 @@ import (
 	"github.com/pingcap/tidb/structure"
 	"github.com/pingcap/tidb/util/dbterror"
 	"github.com/pingcap/tidb/util/logutil"
-	placement "github.com/pingcap/tidb/util/placement_policy"
+	placement "github.com/pingcap/tidb/util/placementpolicy"
 	"go.uber.org/zap"
 )
 
diff --git a/util/placement_policy/policy.go b/util/placementpolicy/policy.go
similarity index 94%
rename from util/placement_policy/policy.go
rename to util/placementpolicy/policy.go
index 84a5ab73f3d22..4768e76ed43aa 100644
--- a/util/placement_policy/policy.go
+++ b/util/placementpolicy/policy.go
@@ -12,13 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package placement_policy
+package placementpolicy
 
 import (
 	"github.com/pingcap/parser/model"
 )
 
-// PolicyInfo is the struct to store the placement_policy policy.
+// PolicyInfo is the struct to store the placement policy.
 type PolicyInfo struct {
 	ID                  int64             `json:"id"`
 	Name                model.CIStr       `json:"name"`

From 5dd879875e687c6b57420128915622e95f2c03de Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Fri, 20 Aug 2021 19:44:12 +0800
Subject: [PATCH 16/18] fix test

Signed-off-by: ailinkid <314806019@qq.com>
---
 meta/meta.go      | 26 ++++++++++++++------------
 meta/meta_test.go | 39 ++++++++++++++-------------------------
 2 files changed, 28 insertions(+), 37 deletions(-)

diff --git a/meta/meta.go b/meta/meta.go
index 34bd78f4fca11..3d218b5177281 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -352,20 +352,22 @@ func (m *Meta) checkTableNotExists(dbKey []byte, tableKey []byte) error {
 
 // CreatePolicy creates a policy.
 func (m *Meta) CreatePolicy(policy *placement.PolicyInfo) error {
-	// Autofill the policy ID.
-	policyIDMutex.Lock()
-	genID, err := m.txn.Inc(mPolicyGlobalID, 1)
-	if err != nil {
-		return errors.Trace(err)
+	if policy.ID != 0 {
+		policyKey := m.policyKey(policy.ID)
+		if err := m.checkPolicyNotExists(policyKey); err != nil {
+			return errors.Trace(err)
+		}
+	} else {
+		// Autofill the policy ID.
+		policyIDMutex.Lock()
+		genID, err := m.txn.Inc(mPolicyGlobalID, 1)
+		if err != nil {
+			return errors.Trace(err)
+		}
+		policyIDMutex.Unlock()
+		policy.ID = genID
 	}
-	policyIDMutex.Unlock()
-
-	policy.ID = genID
 	policyKey := m.policyKey(policy.ID)
-
-	if err := m.checkPolicyNotExists(policyKey); err != nil {
-		return errors.Trace(err)
-	}
 	data, err := json.Marshal(policy)
 	if err != nil {
 		return errors.Trace(err)
diff --git a/meta/meta_test.go b/meta/meta_test.go
index e5e754d76592e..d5512a1145ced 100644
--- a/meta/meta_test.go
+++ b/meta/meta_test.go
@@ -25,11 +25,11 @@ import (
 
 	"github.com/pingcap/errors"
 	"github.com/pingcap/parser/model"
-	"github.com/pingcap/tidb/ddl/placement"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/meta"
 	"github.com/pingcap/tidb/store/mockstore"
 	"github.com/pingcap/tidb/testkit"
+	"github.com/pingcap/tidb/util/placementpolicy"
 	"github.com/stretchr/testify/require"
 )
 
@@ -49,33 +49,22 @@ func TestPlacementPolicy(t *testing.T) {
 
 	// test the independent policy ID allocation.
 	m := meta.NewMeta(txn)
-	id, err := m.GenPolicyID()
-	require.NoError(t, err)
-	require.Equal(t, int64(1), id)
-
-	id, err = m.GetPolicyID()
-	require.NoError(t, err)
-	require.Equal(t, int64(1), id)
-
-	id, err = m.GenPolicyID()
-	require.NoError(t, err)
-	require.Equal(t, int64(2), id)
 
 	// test the meta storage of placemnt policy.
-	policy := &placement.Policy{
-		ID:                1,
-		Name:              model.NewCIStr("aa"),
-		PrimaryRegion:     "my primary",
-		Regions:           "my regions",
-		Leaders:           1,
-		Followers:         2,
-		Voters:            3,
-		Schedule:          "even",
-		Constraints:       "+disk=ssd",
-		LeaderConstraints: "+zone=shanghai",
+	policy := &placementpolicy.PolicyInfo{
+		Name:               model.NewCIStr("aa"),
+		PrimaryRegion:      "my primary",
+		Regions:            "my regions",
+		Learners:           1,
+		Followers:          2,
+		Voters:             3,
+		Schedule:           "even",
+		Constraints:        "+disk=ssd",
+		LearnerConstraints: "+zone=shanghai",
 	}
 	err = m.CreatePolicy(policy)
 	require.NoError(t, err)
+	require.Equal(t, policy.ID, int64(1))
 
 	err = m.CreatePolicy(policy)
 	require.NotNil(t, err)
@@ -87,7 +76,7 @@ func TestPlacementPolicy(t *testing.T) {
 
 	// mock updating the placement policy.
 	policy.Name = model.NewCIStr("bb")
-	policy.LeaderConstraints = "+zone=nanjing"
+	policy.LearnerConstraints = "+zone=nanjing"
 	err = m.UpdatePolicy(policy)
 	require.NoError(t, err)
 
@@ -97,7 +86,7 @@ func TestPlacementPolicy(t *testing.T) {
 
 	ps, err := m.ListPolicies()
 	require.NoError(t, err)
-	require.Equal(t, []*placement.Policy{policy}, ps)
+	require.Equal(t, []*placementpolicy.PolicyInfo{policy}, ps)
 
 	err = txn.Commit(context.Background())
 	require.NoError(t, err)

From f1f392443e7f132e8e6a7e268dd80fa94e4806a9 Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Sat, 21 Aug 2021 09:57:09 +0800
Subject: [PATCH 17/18] change typeUnknow to 0

Signed-off-by: ailinkid <314806019@qq.com>
---
 meta/meta.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/meta/meta.go b/meta/meta.go
index 3d218b5177281..21e8558aab2f9 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -88,8 +88,8 @@ const (
 	// 0xC0 - 0xFF: Reserved
 
 	// type means how to handle the serialized data.
+	typeUnknown int = 0
 	typeJSON    int = 1
-	typeUnknown int = 2
 	// todo: customized handler.
 )
 

From 9df17d00ddc9d5484cf227bfa177bac6366b741e Mon Sep 17 00:00:00 2001
From: ailinkid <314806019@qq.com>
Date: Mon, 23 Aug 2021 16:50:16 +0800
Subject: [PATCH 18/18] add magic byte compatibility check

Signed-off-by: ailinkid <314806019@qq.com>
---
 meta/meta.go | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/meta/meta.go b/meta/meta.go
index 21e8558aab2f9..e4872e7d08740 100644
--- a/meta/meta.go
+++ b/meta/meta.go
@@ -693,9 +693,11 @@ func detachMagicByte(value []byte) ([]byte, error) {
 	magic, data := value[:1], value[1:]
 	switch whichMagicType(magic[0]) {
 	case typeJSON:
+		if magic[0] != CurrentMagicByteVer {
+			return nil, errors.New("incompatible magic type handling module")
+		}
 		return data, nil
 	default:
-		//
 		return nil, errors.New("unknown magic type handling module")
 	}
 }