code: public void backup(Path pathToDir) {
          if (!isPersistent()) {
              throw new BitsyException(BitsyErrorCodes.OPERATION_UNDEFINED_FOR_NON_PERSISTENT_GRAPHS, "Transaction log threshold is only defined for persistent graphs (with a defined path to DB)");
          } else {
              ((FileBackedMemoryGraphStore)graphStore).backup(pathToDir);
          }
      }
docs: This method backs up the database while it is still operational. Only one backup can be in progress at a time.
  
  @param pathToDir directory to which the database must be backed up.