session: use mDDLTableVersion key to control backfill tables (#40984)

close #40980

meta/meta.go

@@ -122,6 +122,25 @@ var (
 	ErrInvalidString = dbterror.ClassMeta.NewStd(errno.ErrInvalidCharacterString)
 )
 
+// DDLTableVersion is to display ddl related table versions
+type DDLTableVersion int
+
+const (
+	// InitDDLTableVersion is the original version.
+	InitDDLTableVersion DDLTableVersion = 0
+	// BaseDDLTableVersion is for support concurrent DDL, it added tidb_ddl_job, tidb_ddl_reorg and tidb_ddl_history.
+	BaseDDLTableVersion DDLTableVersion = 1
+	// MDLTableVersion is for support MDL tables.
+	MDLTableVersion DDLTableVersion = 2
+	// BackfillTableVersion is for support distributed reorg stage, it added tidb_ddl_backfill, tidb_ddl_backfill_history.
+	BackfillTableVersion DDLTableVersion = 3
+)
+
+// Bytes returns the byte slice.
+func (ver DDLTableVersion) Bytes() []byte {
+	return []byte(strconv.Itoa(int(ver)))
+}
+
 // Meta is for handling meta information in a transaction.
 type Meta struct {
 	txn        *structure.TxStructure
@@ -619,15 +638,25 @@ func (m *Meta) CreateTableOrView(dbID int64, tableInfo *model.TableInfo) error {
 }
 
 // SetDDLTables write a key into storage.
-func (m *Meta) SetDDLTables() error {
-	err := m.txn.Set(mDDLTableVersion, []byte("1"))
+func (m *Meta) SetDDLTables(ddlTableVersion DDLTableVersion) error {
+	err := m.txn.Set(mDDLTableVersion, ddlTableVersion.Bytes())
 	return errors.Trace(err)
 }
 
-// SetMDLTables write a key into storage.
-func (m *Meta) SetMDLTables() error {
-	err := m.txn.Set(mDDLTableVersion, []byte("2"))
-	return errors.Trace(err)
+// CheckDDLTableVersion check if the tables related to concurrent DDL exists.
+func (m *Meta) CheckDDLTableVersion() (DDLTableVersion, error) {
+	v, err := m.txn.Get(mDDLTableVersion)
+	if err != nil {
+		return -1, errors.Trace(err)
+	}
+	if string(v) == "" {
+		return InitDDLTableVersion, nil
+	}
+	ver, err := strconv.Atoi(string(v))
+	if err != nil {
+		return -1, errors.Trace(err)
+	}
+	return DDLTableVersion(ver), nil
 }
 
 // CreateMySQLDatabaseIfNotExists creates mysql schema and return its DB ID.
@@ -666,24 +695,6 @@ func (m *Meta) GetSystemDBID() (int64, error) {
 	return 0, nil
 }
 
-// CheckDDLTableExists check if the tables related to concurrent DDL exists.
-func (m *Meta) CheckDDLTableExists() (bool, error) {
-	v, err := m.txn.Get(mDDLTableVersion)
-	if err != nil {
-		return false, errors.Trace(err)
-	}
-	return len(v) != 0, nil
-}
-
-// CheckMDLTableExists check if the tables related to concurrent DDL exists.
-func (m *Meta) CheckMDLTableExists() (bool, error) {
-	v, err := m.txn.Get(mDDLTableVersion)
-	if err != nil {
-		return false, errors.Trace(err)
-	}
-	return bytes.Equal(v, []byte("2")), nil
-}
-
 // SetMetadataLock sets the metadata lock.
 func (m *Meta) SetMetadataLock(b bool) error {
 	var data []byte

session/bootstrap_test.go

@@ -152,10 +152,12 @@ func TestBootstrapWithError(t *testing.T) {
 		se.txn.init()
 		se.mu.values = make(map[fmt.Stringer]interface{})
 		se.SetValue(sessionctx.Initing, true)
-		err := InitDDLJobTables(store)
+		err := InitDDLJobTables(store, meta.BaseDDLTableVersion)
 		require.NoError(t, err)
 		err = InitMDLTable(store)
 		require.NoError(t, err)
+		err = InitDDLJobTables(store, meta.BackfillTableVersion)
+		require.NoError(t, err)
 		dom, err := domap.Get(store)
 		require.NoError(t, err)
 		domain.BindDomain(se, dom)
@@ -215,10 +217,43 @@ func TestBootstrapWithError(t *testing.T) {
 	require.Equal(t, []byte("True"), row.GetBytes(0))
 	require.NoError(t, r.Close())
 
+	mustExec(t, se, "SELECT * from mysql.tidb_ddl_backfill")
+	mustExec(t, se, "SELECT * from mysql.tidb_ddl_backfill_history")
+
 	// Check tidb_ttl_table_status table
 	mustExec(t, se, "SELECT * from mysql.tidb_ttl_table_status")
 }
 
+func TestDDLTableCreateBackfillTable(t *testing.T) {
+	store, dom := createStoreAndBootstrap(t)
+	defer func() { require.NoError(t, store.Close()) }()
+	se := createSessionAndSetID(t, store)
+
+	txn, err := store.Begin()
+	require.NoError(t, err)
+	m := meta.NewMeta(txn)
+	ver, err := m.CheckDDLTableVersion()
+	require.NoError(t, err)
+	require.GreaterOrEqual(t, ver, meta.BackfillTableVersion)
+
+	// downgrade `mDDLTableVersion`
+	m.SetDDLTables(meta.MDLTableVersion)
+	mustExec(t, se, "drop table mysql.tidb_ddl_backfill")
+	mustExec(t, se, "drop table mysql.tidb_ddl_backfill_history")
+	err = txn.Commit(context.Background())
+	require.NoError(t, err)
+
+	// to upgrade session for create ddl related tables
+	dom.Close()
+	dom, err = BootstrapSession(store)
+	require.NoError(t, err)
+
+	se = createSessionAndSetID(t, store)
+	mustExec(t, se, "select * from mysql.tidb_ddl_backfill")
+	mustExec(t, se, "select * from mysql.tidb_ddl_backfill_history")
+	dom.Close()
+}
+
 // TestUpgrade tests upgrading
 func TestUpgrade(t *testing.T) {
 	ctx := context.Background()

session/session.go

@@ -3103,41 +3103,29 @@ func splitAndScatterTable(store kv.Storage, tableIDs []int64) {
 	}
 }
 
-// InitDDLJobTables is to create tidb_ddl_job, tidb_ddl_reorg, tidb_ddl_history, tidb_ddl_backfill and tidb_ddl_backfill_history.
-func InitDDLJobTables(store kv.Storage) error {
+// InitDDLJobTables is to create tidb_ddl_job, tidb_ddl_reorg and tidb_ddl_history, or tidb_ddl_backfill and tidb_ddl_backfill_history.
+func InitDDLJobTables(store kv.Storage, targetVer meta.DDLTableVersion) error {
+	targetTables := DDLJobTables
+	if targetVer == meta.BackfillTableVersion {
+		targetTables = BackfillTables
+	}
 	return kv.RunInNewTxn(kv.WithInternalSourceType(context.Background(), kv.InternalTxnDDL), store, true, func(ctx context.Context, txn kv.Transaction) error {
 		t := meta.NewMeta(txn)
-		exists, err := t.CheckDDLTableExists()
-		if err != nil {
+		tableVer, err := t.CheckDDLTableVersion()
+		if err != nil || tableVer >= targetVer {
 			return errors.Trace(err)
 		}
 		dbID, err := t.CreateMySQLDatabaseIfNotExists()
 		if err != nil {
 			return err
 		}
-		if exists {
-			return initBackfillJobTables(store, t, dbID)
-		}
-
-		if err = createAndSplitTables(store, t, dbID, DDLJobTables); err != nil {
-			return err
-		}
-		if err = initBackfillJobTables(store, t, dbID); err != nil {
+		if err = createAndSplitTables(store, t, dbID, targetTables); err != nil {
 			return err
 		}
-		return t.SetDDLTables()
+		return t.SetDDLTables(targetVer)
 	})
 }
 
-// initBackfillJobTables is to create tidb_ddl_backfill and tidb_ddl_backfill_history.
-func initBackfillJobTables(store kv.Storage, t *meta.Meta, dbID int64) error {
-	tblExist, err := t.CheckTableExists(dbID, BackfillTables[0].id)
-	if err != nil || tblExist {
-		return errors.Trace(err)
-	}
-	return createAndSplitTables(store, t, dbID, BackfillTables)
-}
-
 func createAndSplitTables(store kv.Storage, t *meta.Meta, dbID int64, tables []tableBasicInfo) error {
 	tableIDs := make([]int64, 0, len(tables))
 	for _, tbl := range tables {
@@ -3169,8 +3157,8 @@ func createAndSplitTables(store kv.Storage, t *meta.Meta, dbID int64, tables []t
 func InitMDLTable(store kv.Storage) error {
 	return kv.RunInNewTxn(kv.WithInternalSourceType(context.Background(), kv.InternalTxnDDL), store, true, func(ctx context.Context, txn kv.Transaction) error {
 		t := meta.NewMeta(txn)
-		exists, err := t.CheckMDLTableExists()
-		if err != nil || exists {
+		ver, err := t.CheckDDLTableVersion()
+		if err != nil || ver >= meta.MDLTableVersion {
 			return errors.Trace(err)
 		}
 		dbID, err := t.CreateMySQLDatabaseIfNotExists()
@@ -3195,7 +3183,7 @@ func InitMDLTable(store kv.Storage) error {
 			return errors.Trace(err)
 		}
 
-		return t.SetMDLTables()
+		return t.SetDDLTables(meta.MDLTableVersion)
 	})
 }
 
@@ -3272,14 +3260,18 @@ func BootstrapSession(store kv.Storage) (*domain.Domain, error) {
 			return nil, err
 		}
 	}
-	err := InitDDLJobTables(store)
+	err := InitDDLJobTables(store, meta.BaseDDLTableVersion)
 	if err != nil {
 		return nil, err
 	}
 	err = InitMDLTable(store)
 	if err != nil {
 		return nil, err
 	}
+	err = InitDDLJobTables(store, meta.BackfillTableVersion)
+	if err != nil {
+		return nil, err
+	}
 	ver := getStoreBootstrapVersion(store)
 	if ver == notBootstrapped {
 		runInBootstrapSession(store, bootstrap)

session/session_test.go

@@ -37,10 +37,16 @@ func TestInitMetaTable(t *testing.T) {
 		tk.MustExec(sql.SQL)
 	}
 
+	for _, sql := range session.BackfillTables {
+		tk.MustExec(sql.SQL)
+	}
+
 	tbls := map[string]struct{}{
-		"tidb_ddl_job":     {},
-		"tidb_ddl_reorg":   {},
-		"tidb_ddl_history": {},
+		"tidb_ddl_job":              {},
+		"tidb_ddl_reorg":            {},
+		"tidb_ddl_history":          {},
+		"tidb_ddl_backfill":         {},
+		"tidb_ddl_backfill_history": {},
 	}
 
 	for tbl := range tbls {