parent.replaceChild(mapJoinOp, hashTableSinkOp);
// keep the parent id correct
smallTablesParentOp.add(parent);
// create an new operator: HashTable DummyOpeator, which share the table desc
HashTableDummyDesc desc = new HashTableDummyDesc();
HashTableDummyOperator dummyOp = (HashTableDummyOperator) OperatorFactory.get(desc);
TableDesc tbl;
if (parent.getSchema() == null) {
if (parent instanceof TableScanOperator) {