presto-main/src/main/java/io/prestosql/operator/aggregation/GenericAccumulatorFactory.java/OrderingAccumulator/evaluateFinal
class OrderingAccumulator:        @Override
        public void evaluateFinal(BlockBuilder blockBuilder)
        {
            pagesIndex.sort(orderByChannels, orderings);
            Iterator<Page> pagesIterator = pagesIndex.getSortedPages();
            pagesIterator.forEachRemaining(accumulator::addInput);
            accumulator.evaluateFinal(blockBuilder);
        }