presto-main/src/main/java/io/prestosql/operator/SetBuilderOperator.java/SetBuilderOperator/finish
class SetBuilderOperator:    @Override
    public void finish()
    {
        if (finished) {
            return;
        }

        ChannelSet channelSet = channelSetBuilder.build();
        setSupplier.setChannelSet(channelSet);
        operatorContext.recordOutput(channelSet.getEstimatedSizeInBytes(), channelSet.size());
        finished = true;
    }