code: func (w *SegmentWAL) LogDeletes(stones []Stone) error {
  	buf := w.getBuffer()
  
  	flag := w.encodeDeletes(buf, stones)
  
  	w.mtx.Lock()
  	defer w.mtx.Unlock()
  
  	err := w.write(WALEntryDeletes, flag, buf.Get())
  
  	w.putBuffer(buf)
  
  	if err != nil {
  		return errors.Wrap(err, "log series")
  	}
  	tf := w.head()
  
  	for _, s := range stones {
  		for _, iv := range s.intervals {
  			if tf.maxTime < iv.Maxt {
  				tf.maxTime = iv.Maxt
  			}
  		}
  	}
  	return nil
  }
docs: // LogDeletes write a batch of new deletes to the log.