code: public void saveHWMark(String source, long hwm) {
          WaterMarkEntry wmEntry = sourceWaterMarkMap.get(source);
          if (wmEntry != null) {
              wmEntry.setHWMScn(Math.max(hwm, wmEntry.getHWMScn()));
          } else {
              wmEntry = new WaterMarkEntry(source);
              wmEntry.setHWMScn(hwm);
  
              sourceWaterMarkMap.put(source, wmEntry);
          }
      }
docs: Saves the high water mark of a source.
  This method has the same functionality as {@link #setHWMScn(String, long)}.
  
  @param source - the source
  @param hwm    - the high water mark