code: func (db *DB) HMclear(keys ...[]byte) (int64, error) {
  	t := db.hashBatch
  	t.Lock()
  	defer t.Unlock()
  
  	for _, key := range keys {
  		if err := checkKeySize(key); err != nil {
  			return 0, err
  		}
  
  		db.hDelete(t, key)
  		db.rmExpire(t, HashType, key)
  	}
  
  	err := t.Commit()
  	return int64(len(keys)), err
  }
docs: // HMclear cleans multi data.