*: fix the duplicate entry error when using BR to restore a NONCLUSTERED AUTO_ID_CACHE=1 table

br/pkg/backup/client.go

@@ -633,6 +633,11 @@ func BuildBackupSchemas(
 			default:
 				if tableInfo.SepAutoInc() {
 					globalAutoID, err = autoIDAccess.IncrementID(tableInfo.Version).Get()
+					// For a nonclustered table with auto_increment column, both auto_increment_id and _tidb_rowid are required.
+					// See also https://github.com/pingcap/tidb/issues/46093
+					if rowID, err1 := autoIDAccess.RowID().Get(); err1 == nil {
+						tableInfo.AutoIncIDExtra = rowID + 1
+					}
 				} else {
 					globalAutoID, err = autoIDAccess.RowID().Get()
 				}

br/pkg/lightning/common/common.go

@@ -89,17 +89,26 @@ func getGlobalAutoIDAlloc(store kv.Storage, dbID int64, tblInfo *model.TableInfo
 	hasAutoIncID := tblInfo.GetAutoIncrementColInfo() != nil
 	hasAutoRandID := tblInfo.ContainsAutoRandomBits()
 
-	// Current TiDB has some limitations for auto ID.
+	// Before MySQL compatible AUTO_INCREMENT, TiDB has some limitations:
 	// 1. Auto increment ID and auto row ID are using the same RowID allocator.
 	//    See https://github.com/pingcap/tidb/issues/982.
 	// 2. Auto random column must be a clustered primary key. That is to say,
 	//    there is no implicit row ID for tables with auto random column.
 	// 3. There is at most one auto column in a table.
 	// Therefore, we assume there is only one auto column in a table and use RowID allocator if possible.
+	//
+	// If AUTO_ID_CACHE=1 is set (i.e. MySQL compatible AUTO_INCREMENT), the limitations do not hold anymore.
 	switch {
-	case hasRowID || hasAutoIncID:
+	case hasRowID:
 		return autoid.NewAllocator(store, dbID, tblInfo.ID, tblInfo.IsAutoIncColUnsigned(),
 			autoid.RowIDAllocType, noCache, tblVer), nil
+	case hasAutoIncID:
+		allocType := autoid.RowIDAllocType
+		if tblInfo.SepAutoInc() {
+			allocType = autoid.AutoIncrementType
+		}
+		return autoid.NewAllocator(store, dbID, tblInfo.ID, tblInfo.IsAutoIncColUnsigned(),
+			allocType, noCache, tblVer), nil
 	case hasAutoRandID:
 		return autoid.NewAllocator(store, dbID, tblInfo.ID, tblInfo.IsAutoRandomBitColUnsigned(),
 			autoid.AutoRandomType, noCache, tblVer), nil

ddl/ddl_api.go

@@ -2628,6 +2628,12 @@ func (d *ddl) createTableWithInfoPost(
 			return errors.Trace(err)
 		}
 	}
+	// For issue https://github.com/pingcap/tidb/issues/46093
+	if tbInfo.AutoIncIDExtra != 0 {
+		if err = d.handleAutoIncID(tbInfo, schemaID, tbInfo.AutoIncIDExtra-1, autoid.RowIDAllocType); err != nil {
+			return errors.Trace(err)
+		}
+	}
 	if tbInfo.AutoRandID > 1 {
 		// Default tableAutoRandID base is 0.
 		// If the first ID is expected to greater than 1, we need to do rebase.

parser/model/model.go

@@ -458,14 +458,29 @@ type TableInfo struct {
 	// 1 for the clustered index created > 5.0.0 RC.
 	CommonHandleVersion uint16 `json:"common_handle_version"`
 
-	Comment         string `json:"comment"`
-	AutoIncID       int64  `json:"auto_inc_id"`
-	AutoIdCache     int64  `json:"auto_id_cache"` //nolint:revive
-	AutoRandID      int64  `json:"auto_rand_id"`
-	MaxColumnID     int64  `json:"max_col_id"`
-	MaxIndexID      int64  `json:"max_idx_id"`
-	MaxForeignKeyID int64  `json:"max_fk_id"`
-	MaxConstraintID int64  `json:"max_cst_id"`
+	Comment   string `json:"comment"`
+	AutoIncID int64  `json:"auto_inc_id"`
+
+	// Only used by BR when:
+	// 1. SepAutoInc() is true
+	// 2. The table is nonclustered and has auto_increment column.
+	// In that case, both auto_increment_id and tidb_rowid need to be backup & recover.
+	// See also https://github.com/pingcap/tidb/issues/46093
+	//
+	// It should have been named TiDBRowID, but for historial reasons, we do not use separate meta key for _tidb_rowid and auto_increment_id,
+	// and field `AutoIncID` is used to serve both _tidb_rowid and auto_increment_id.
+	// If we introduce a TiDBRowID here, it could make furthur misunderstanding:
+	//	in most cases, AutoIncID is _tidb_rowid and TiDBRowID is null
+	//      but in some cases, AutoIncID is auto_increment_id and TiDBRowID is _tidb_rowid
+	// So let's just use another name AutoIncIDExtra to avoid misconception.
+	AutoIncIDExtra int64 `json:"auto_inc_id_extra,omitempty"`
+
+	AutoIdCache     int64 `json:"auto_id_cache"` //nolint:revive
+	AutoRandID      int64 `json:"auto_rand_id"`
+	MaxColumnID     int64 `json:"max_col_id"`
+	MaxIndexID      int64 `json:"max_idx_id"`
+	MaxForeignKeyID int64 `json:"max_fk_id"`
+	MaxConstraintID int64 `json:"max_cst_id"`
 	// UpdateTS is used to record the timestamp of updating the table's schema information.
 	// These changing schema operations don't include 'truncate table' and 'rename table'.
 	UpdateTS uint64 `json:"update_timestamp"`