presto-main/src/main/java/io/prestosql/operator/OrderByOperator.java/OrderByOperator/getSpilledPages
class OrderByOperator:    private List<WorkProcessor<Page>> getSpilledPages()
    {
        if (!spiller.isPresent()) {
            return ImmutableList.of();
        }

        return spiller.get().getSpills().stream()
                .map(WorkProcessor::fromIterator)
                .collect(toImmutableList());
    }