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