@Override
  public VectorizedRowBatch produceNextBatch() {
    VectorizedRowBatch ret = null;

    do {
      if (null != iterator && iterator.hasNext()) {
        ret = iterator.next();
        break;
      }

      if (index >= iterables.length) {
        ret = emptyBatch;
        break;
      }

      iterator = iterables[index].iterator();
      ++index;
    } while (true);

    return ret;
  }
Concatenates many arbitrary FakeVectorRowBatch sources as one single source.
Used in unit test only.
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/util/FakeVectorRowBatchFromConcat.java