@VisibleForTesting
  @Override
  public void setTestMapJoinTableContainer(int posSmallTable,
      MapJoinTableContainer testMapJoinTableContainer,
      MapJoinTableContainerSerDe mapJoinTableContainerSerDe) {

    mapJoinTables[posSingleVectorMapJoinSmallTable] = testMapJoinTableContainer;

    setUpHashTable();
  }
This override lets us substitute our own fast vectorized hash table loader.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/mapjoin/VectorMapJoinCommonOperator.java