protected void displayBatchColumns(VectorizedRowBatch batch, String batchName) {
    LOG.debug(getLoggingPrefix() + " VectorMapJoinCommonOperator commonSetup " + batchName + " column count " + batch.numCols);
    for (int column = 0; column < batch.numCols; column++) {
      LOG.debug(getLoggingPrefix() + " VectorMapJoinCommonOperator commonSetup " + batchName + "     column " + column + " type " + (batch.cols[column] == null ? "NULL" : batch.cols[column].getClass().getSimpleName()));
    }
  }
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