code: public void add(BatchEntry batchEntry) throws DatabaseEngineException {
          bufferLock.lock();
          try {
              buffer.add(batchEntry);
              batch--;
          } finally {
              bufferLock.unlock();
          }
          if (batch <= 0) {
              flush();
          }
      }
docs: Adds the fields to the batch.
  
  @param batchEntry The batch entry.
  @throws DatabaseEngineException If an error with the database occurs.