code: func (api *API) AvailableShardsByIndex(ctx context.Context) map[string]*roaring.Bitmap {
  	span, _ := tracing.StartSpanFromContext(ctx, "API.AvailableShardsByIndex")
  	defer span.Finish()
  	return api.holder.availableShardsByIndex()
  }
docs: // AvailableShardsByIndex returns bitmaps of shards with available by index name.