private int[] getByteColumnVectorColumns(VectorColumnMapping mapping) {
    return getByteColumnVectorColumns(mapping.getOutputColumns(), mapping.getTypeInfos());
  }
Determine from a mapping which columns are BytesColumnVector columns.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/mapjoin/VectorMapJoinCommonOperator.java