presto-main/src/main/java/io/prestosql/spiller/GenericPartitioningSpiller.java/GenericPartitioningSpiller/getSpilledPages
class GenericPartitioningSpiller:    @Override
    public synchronized Iterator<Page> getSpilledPages(int partition)
    {
        readingStarted = true;
        getFutureValue(flush(partition));
        spilledPartitions.remove(partition);
        return getSpiller(partition).getSpilledPages();
    }