private void allocateArrays(int count) {
    projectionColumnNums = new int[count];
    typeInfos = new TypeInfo[count];
    objectInspectors = new ObjectInspector[count];
  }
This class extracts specified VectorizedRowBatch row columns into writables.

The caller provides the data types and projection column numbers of a subset of the columns
to extract.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorExtractRow.java