executor: support FAST ADMIN CHECK for prefix index

pkg/executor/builder.go

@@ -517,12 +517,6 @@ func (b *executorBuilder) buildCheckTable(v *plannercore.CheckTable) exec.Execut
 			noMVIndexOrPrefixIndexOrColumnarIndex = false
 			break
 		}
-		for _, col := range idx.Columns {
-			if col.Length != types.UnspecifiedLength {
-				noMVIndexOrPrefixIndexOrColumnarIndex = false
-				break
-			}
-		}
 		if !noMVIndexOrPrefixIndexOrColumnarIndex {
 			break
 		}

pkg/executor/check_table_index.go

@@ -384,10 +384,10 @@ func (w *checkIndexWorker) HandleTask(task checkIndexTask, _ func(workerpool.Non
 	indexColNames := make([]string, len(idxInfo.Columns))
 	for i, col := range idxInfo.Columns {
 		tblCol := tblMeta.Columns[col.Offset]
-		if tblCol.IsVirtualGenerated() && tblCol.Hidden {
-			indexColNames[i] = tblCol.GeneratedExprString
+		if col.Length == types.UnspecifiedLength {
+			indexColNames[i] = ColumnName(tblCol.Name.O)
 		} else {
-			indexColNames[i] = ColumnName(col.Name.O)
+			indexColNames[i] = fmt.Sprintf("CAST(%s AS CHAR(%d))", ColumnName(col.Name.O), col.Length)
 		}
 	}
 	indexColumns := strings.Join(indexColNames, ",")

pkg/planner/core/logical_plan_builder.go

@@ -38,6 +38,7 @@ import (
 	"github.com/pingcap/tidb/pkg/expression/exprctx"
 	"github.com/pingcap/tidb/pkg/infoschema"
 	"github.com/pingcap/tidb/pkg/kv"
+	"github.com/pingcap/tidb/pkg/meta/autoid"
 	"github.com/pingcap/tidb/pkg/meta/metadef"
 	"github.com/pingcap/tidb/pkg/meta/model"
 	"github.com/pingcap/tidb/pkg/parser"
@@ -4431,6 +4432,44 @@ func (b *PlanBuilder) buildDataSourceFromCTEMerge(ctx context.Context, cte *ast.
 	return p, nil
 }
 
+// buildTableForAdminCheckSQL make a copy of table info if necessary.
+// Since we want to utilize MVIndex/prefix index/virtual column to read the data in FAST ADMIN CHECK,
+// to prevent from adding many hacky code in planner, we create a mock table info without these meta.
+// So we can guarantee to use index only scan for index SQL in FAST ADMIN CHECK.
+func buildTableForAdminCheckSQL(tbl table.Table) (table.Table, error) {
+	tblInfo := tbl.Meta()
+
+	// If table contains any index column with prefix length/hidden column/MVIndex, ,
+	needRebuildInfo := false
+	for _, idx := range tblInfo.Indices {
+		if idx.MVIndex {
+			needRebuildInfo = true
+		}
+		for _, col := range idx.Columns {
+			if col.Length != types.UnspecifiedLength || tblInfo.Columns[col.Offset].Hidden {
+				needRebuildInfo = true
+			}
+		}
+	}
+
+	if !needRebuildInfo {
+		return tbl, nil
+	}
+
+	mockInfo := tbl.Meta().Clone()
+	for _, idx := range mockInfo.Indices {
+		idx.MVIndex = false
+		for _, col := range idx.Columns {
+			col.Length = types.UnspecifiedLength
+			tblCol := mockInfo.Columns[col.Offset]
+			tblCol.FieldType.SetArray(false)
+			tblCol.Hidden = false
+		}
+	}
+
+	return tables.TableFromMeta(autoid.NewAllocators(false, nil), mockInfo)
+}
+
 func (b *PlanBuilder) buildDataSource(ctx context.Context, tn *ast.TableName, asName *ast.CIStr) (base.LogicalPlan, error) {
 	b.optFlag |= rule.FlagPredicateSimplification
 	dbName := tn.Schema
@@ -4458,6 +4497,12 @@ func (b *PlanBuilder) buildDataSource(ctx context.Context, tn *ast.TableName, as
 		return nil, err
 	}
 
+	// if kv.GetInternalSourceType(ctx) == kv.InternalTxnAdmin {
+	if tbl, err = buildTableForAdminCheckSQL(tbl); err != nil {
+		return nil, err
+	}
+	// }
+
 	tbl, err = tryLockMDLAndUpdateSchemaIfNecessary(ctx, b.ctx, dbName, tbl, b.is)
 	if err != nil {
 		return nil, err