code: private Integer _unsafe_add(Record r) {
          Integer newId = data.atomicNextAvailableRecordId.getAndIncrement();
          data.records.put(newId, r);
  
          return newId;
      }
docs: Adds the record in the dataset without updating the Meta. The add method
  returns the id of the new record.
  
  @param r
  @return