presto-main/src/main/java/io/prestosql/operator/Aggregator.java/Aggregator/evaluate
class Aggregator:    public void evaluate(BlockBuilder blockBuilder)
    {
        if (step.isOutputPartial()) {
            aggregation.evaluateIntermediate(blockBuilder);
        }
        else {
            aggregation.evaluateFinal(blockBuilder);
        }
    }