presto-main/src/main/java/io/prestosql/operator/exchange/LocalExchangeSourceOperator.java/LocalExchangeSourceOperator/getOutput
class LocalExchangeSourceOperator:    @Override
    public Page getOutput()
    {
        Page page = source.removePage();
        if (page != null) {
            operatorContext.recordProcessedInput(page.getSizeInBytes(), page.getPositionCount());
        }
        return page;
    }