presto-main/src/main/java/io/prestosql/operator/ExchangeOperator.java/ExchangeOperator/getOutput
class ExchangeOperator:    @Override
    public Page getOutput()
    {
        SerializedPage page = exchangeClient.pollPage();
        if (page == null) {
            return null;
        }

        operatorContext.recordNetworkInput(page.getSizeInBytes(), page.getPositionCount());

        Page deserializedPage = serde.deserialize(page);
        operatorContext.recordProcessedInput(deserializedPage.getSizeInBytes(), page.getPositionCount());

        return deserializedPage;
    }