code: public Record _unsafe_set(Integer rId, Record r) {
          //move ahead the next id
          data.atomicNextAvailableRecordId.updateAndGet(x -> (x<rId)?Math.max(x+1,rId+1):x);
  
          return data.records.put(rId, r);
      }
docs: Sets the record in a particular position in the dataset, WITHOUT updating
  the internal meta-info and returns the previous value (null if not existed).
  This method is similar to set() and it allows quick updates
  on the dataset. Nevertheless it is not advised to use this method because
  unless you explicitly call the recalculateMeta() method, the meta data
  will be corrupted. If you do use this method, MAKE sure you perform the
  recalculation after you are done with the updates.
  
  @param rId
  @param r
  @return