private void allocateArrays(int count) {
    projectionColumnNums = new int[count];
    Arrays.fill(projectionColumnNums, -1);
    topLevelFields = new Field[count];
  }
@param deserializeRead   Set useExternalBuffer to true to avoid buffer copying and to get
    more efficient reading.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorDeserializeRow.java