docs: public void add(final ExpressionDataPoint dps) {
      metric_uids.addAll(dps.metric_uids);
      
      // TODO - tags intersection
      
      aggregated_tags.addAll(dps.aggregated_tags);
      
      tsuids.addAll(dps.tsuids);
      // TODO - this ain't right. We need to number of dps emitted from HERE. For
      // now we'll just take the first dps size. If it's downsampled then this
      // will be accurate.
      //size += dps.size();
      raw_size += dps.raw_size;
    }