docs: public void updateStat(final int query_index, final QueryStat name, 
        final long value) {
      Map<QueryStat, Long> qs = query_stats.get(query_index);
      long cum_time = value;
      if (qs == null) {
        qs = new HashMap<QueryStat, Long>();
        query_stats.put(query_index, qs);
      }
      
      if (qs.containsKey(name)) {
        cum_time += qs.get(name);
      }
      qs.put(name, cum_time);
    }