code: func WalkMemBuffer(memBuf MemBuffer, f func(k Key, v []byte) error) error {
  	iter, err := memBuf.Iter(nil, nil)
  	if err != nil {
  		return errors.Trace(err)
  	}
  
  	defer iter.Close()
  	for iter.Valid() {
  		if err = f(iter.Key(), iter.Value()); err != nil {
  			return errors.Trace(err)
  		}
  		err = iter.Next()
  		if err != nil {
  			return errors.Trace(err)
  		}
  	}
  
  	return nil
  }
docs: // WalkMemBuffer iterates all buffered kv pairs in memBuf