code: func (q *LevelHistoryDBQueryExecutor) GetHistoryForKey(namespace string, key string) (commonledger.ResultsIterator, error) {
  
  	if ledgerconfig.IsHistoryDBEnabled() == false {
  		return nil, errors.New("history database not enabled")
  	}
  
  	var compositeStartKey []byte
  	var compositeEndKey []byte
  	compositeStartKey = historydb.ConstructPartialCompositeHistoryKey(namespace, key, false)
  	compositeEndKey = historydb.ConstructPartialCompositeHistoryKey(namespace, key, true)
  
  	// range scan to find any history records starting with namespace~key
  	dbItr := q.historyDB.db.GetIterator(compositeStartKey, compositeEndKey)
  	return newHistoryScanner(compositeStartKey, namespace, key, dbItr, q.blockStore), nil
  }
docs: // GetHistoryForKey implements method in interface `ledger.HistoryQueryExecutor`