public void setValPreallocated(int elementNum, int length) {
    vector[elementNum] = currentValue;
    this.start[elementNum] = currentOffset;
    this.length[elementNum] = length;
    // If the current value is the shared buffer, move the next offset forward.
    if (currentValue == sharedBuffer) {
      sharedBufferOffset += length;
    }
  }
Set the length of the preallocated values bytes used.
@param elementNum
@param length
storage-api/src/java/org/apache/hadoop/hive/ql/exec/vector/BytesColumnVector.java