presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/storage/organization/ShardCompactor.java/ShardCompactor/hasNext
class ShardCompactor:        @Override
        public boolean hasNext()
        {
            if (hasMorePositions(currentPage, currentPosition)) {
                return true;
            }

            Page page = getNextPage(pageSource);
            if (isNullOrEmptyPage(page)) {
                return false;
            }
            currentPage = page.getLoadedPage();
            currentPosition = 0;
            return true;
        }