code: func EnsureDatacenters(c context.Context, cfgs []*config.Datacenter) (map[string]int64, error) {
  	t := &DatacentersTable{}
  	if err := t.fetch(c); err != nil {
  		return nil, errors.Annotate(err, "failed to fetch datacenters").Err()
  	}
  	t.computeChanges(c, cfgs)
  	if err := t.add(c); err != nil {
  		return nil, errors.Annotate(err, "failed to add datacenters").Err()
  	}
  	if err := t.remove(c); err != nil {
  		return nil, errors.Annotate(err, "failed to remove datacenters").Err()
  	}
  	if err := t.update(c); err != nil {
  		return nil, errors.Annotate(err, "failed to update datacenters").Err()
  	}
  	return t.ids(c), nil
  }
docs: // EnsureDatacenters ensures the database contains exactly the given datacenters.
  // Returns a map of datacenter names to IDs in the database.