refine comment

Signed-off-by: wjhuang2016 <huangwenjun1997@gmail.com>

ddl/column.go

@@ -1416,7 +1416,7 @@ func (w *updateColumnWorker) cleanRowMap() {
 	}
 }
 
-// BackfillDataInTxn will backfill the table record in a transaction, lock corresponding rowKey, if the value of rowKey is changed.
+// BackfillDataInTxn will backfill the table record in a transaction.
 func (w *updateColumnWorker) BackfillDataInTxn(handleRange reorgBackfillTask) (taskCtx backfillTaskContext, errInTxn error) {
 	oprStartTime := time.Now()
 	errInTxn = kv.RunInNewTxn(context.Background(), w.sessCtx.GetStore(), true, func(ctx context.Context, txn kv.Transaction) error {

ddl/index.go

@@ -1293,8 +1293,8 @@ func (w *addIndexWorker) batchCheckUniqueKey(txn kv.Transaction, idxRecords []*i
 	return nil
 }
 
-// BackfillDataInTxn will backfill table index in a transaction, lock corresponding rowKey, if the value of rowKey is changed,
-// indicate that index columns values may changed, index is not allowed to be added, so the txn will rollback and retry.
+// BackfillDataInTxn will backfill table index in a transaction. If the value of rowKey is changed, there must be some other transactions
+// update the row, result in write conflict, so the txn will rollback and retry.
 // BackfillDataInTxn will add w.batchCnt indices once, default value of w.batchCnt is 128.
 func (w *addIndexWorker) BackfillDataInTxn(handleRange reorgBackfillTask) (taskCtx backfillTaskContext, errInTxn error) {
 	failpoint.Inject("errorMockPanic", func(val failpoint.Value) {