presto-main/src/main/java/io/prestosql/operator/StreamingAggregationOperator.java/StreamingAggregationOperator/addInput
class StreamingAggregationOperator:    @Override
    public void addInput(Page page)
    {
        checkState(!finishing, "Operator is already finishing");
        requireNonNull(page, "page is null");

        processInput(page);
        updateMemoryUsage();
    }