code: func (s *Store) ReapTombstones(index uint64) error {
  	tx := s.db.Txn(true)
  	defer tx.Abort()
  
  	if err := s.kvsGraveyard.ReapTxn(tx, index); err != nil {
  		return fmt.Errorf("failed to reap kvs tombstones: %s", err)
  	}
  
  	tx.Commit()
  	return nil
  }
docs: // ReapTombstones is used to delete all the tombstones with an index
  // less than or equal to the given index. This is used to prevent
  // unbounded storage growth of the tombstones.