presto-hive/src/main/java/io/prestosql/plugin/hive/util/MergingPageIterator.java/MergingPageIterator/computeNext
class MergingPageIterator:        @Override
        protected PagePosition computeNext()
        {
            position++;
            if (position == page.getPositionCount()) {
                return endOfData();
            }
            return new PagePosition(page, position);
        }