code: func (t *QueueManager) SeriesReset(index int) {
  	t.seriesMtx.Lock()
  	defer t.seriesMtx.Unlock()
  
  	// Check for series that are in segments older than the checkpoint
  	// that were not also present in the checkpoint.
  	for k, v := range t.seriesSegmentIndexes {
  		if v < index {
  			delete(t.seriesSegmentIndexes, k)
  			release(t.seriesLabels[k])
  			delete(t.seriesLabels, k)
  		}
  	}
  }
docs: // SeriesReset is used when reading a checkpoint. WAL Watcher should have
  // stored series records with the checkpoints index number, so we can now
  // delete any ref ID's lower than that # from the two maps.