code: func (f *Field) AvailableShards() *roaring.Bitmap {
  	f.mu.RLock()
  	defer f.mu.RUnlock()
  
  	b := f.remoteAvailableShards.Clone()
  	for _, view := range f.viewMap {
  		b = b.Union(view.availableShards())
  	}
  	return b
  }
docs: // AvailableShards returns a bitmap of shards that contain data.