presto-main/src/main/java/io/prestosql/operator/MergeOperator.java/MergeOperator/noMoreSplits
class MergeOperator:    @Override
    public void noMoreSplits()
    {
        mergedPages = mergeSortedPages(
                pageProducers,
                comparator,
                outputChannels,
                outputTypes,
                (pageBuilder, pageWithPosition) -> pageBuilder.isFull(),
                false,
                operatorContext.aggregateUserMemoryContext(),
                operatorContext.getDriverContext().getYieldSignal());
        blockedOnSplits.set(null);
    }