code: func (h *Holder) availableShardsByIndex() map[string]*roaring.Bitmap {
  	m := make(map[string]*roaring.Bitmap)
  	for _, index := range h.Indexes() {
  		m[index.Name()] = index.AvailableShards()
  	}
  	return m
  }
docs: // availableShardsByIndex returns a bitmap of all shards by indexes.