code: func (db *NodeSet) Put(key []byte, value []byte) error {
  	db.lock.Lock()
  	defer db.lock.Unlock()
  
  	if _, ok := db.nodes[string(key)]; ok {
  		return nil
  	}
  	keystr := string(key)
  
  	db.nodes[keystr] = common.CopyBytes(value)
  	db.order = append(db.order, keystr)
  	db.dataSize += len(value)
  
  	return nil
  }
docs: // Put stores a new node in the set