private Timestamp readVectorElementAt(ColumnVector col, int i) {
    if (col instanceof TimestampColumnVector) {
      return ((TimestampColumnVector) col).asScratchTimestamp(i);
    }
    if (col instanceof BytesColumnVector) {
      byte[] timeBytes = ((BytesColumnVector) col).vector[i];
      return decodeTime(timeBytes);
    }
    throw new IllegalArgumentException();
  }
Input array is used to fill the entire size of the vector row batch
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/expressions/TestVectorTimestampExpressions.java