code: func (s *Storage) Querier(ctx context.Context, mint, maxt int64) (storage.Querier, error) {
  	s.mtx.Lock()
  	queryables := s.queryables
  	s.mtx.Unlock()
  
  	queriers := make([]storage.Querier, 0, len(queryables))
  	for _, queryable := range queryables {
  		q, err := queryable.Querier(ctx, mint, maxt)
  		if err != nil {
  			return nil, err
  		}
  		queriers = append(queriers, q)
  	}
  	return storage.NewMergeQuerier(nil, queriers), nil
  }
docs: // Querier returns a storage.MergeQuerier combining the remote client queriers
  // of each configured remote read endpoint.