code: private void saveLastFetchedId(byte[] lastFetchedId) {
          if (lastFetchedId != null) {
              rocksDbWrapper.put(cfNameMetadata, writeOptions, keyLastFetchedId, lastFetchedId);
          }
      }
docs: Saves last-fetched-id.
  
  @param lastFetchedId
  @since 0.4.0.1