presto-main/src/main/java/io/prestosql/operator/Aggregator.java/Aggregator/processPage
class Aggregator:    public void processPage(Page page)
    {
        if (step.isInputRaw()) {
            aggregation.addInput(page);
        }
        else {
            aggregation.addIntermediate(page.getBlock(intermediateChannel));
        }
    }