code: func (t *tx) StartDatastore(table, operation, sql, rollupName string) error {
  	t.mtx.Lock()
  	defer t.mtx.Unlock()
  
  	id, err := t.Tracer.BeginDatastoreSegment(t.id, t.ss.Peek(), table, operation, sql, rollupName)
  	if err != nil {
  		return err
  	}
  	t.ss.Push(id)
  	return nil
  }
docs: // StartDatastore starts a datastore segment.