code: func (tsdbSink *openTSDBSink) putDefaultTags(datapoint *opentsdbclient.DataPoint) {
  	datapoint.Tags[clusterNameTagName] = tsdbSink.clusterName
  }
docs: // putDefaultTags just fills in the default key-value pair for the tags.
  // OpenTSDB requires at least one non-empty tag otherwise the OpenTSDB will return error and the operation of putting
  // datapoint will be failed.