code: func (p *PartitionedMemoryIdx) AddOrUpdate(mkey schema.MKey, data *schema.MetricData, partition int32) (idx.Archive, int32, bool) {
  	return p.Partition[partition].AddOrUpdate(mkey, data, partition)
  }
docs: // AddOrUpdate makes sure a metric is known in the index,
  // and should be called for every received metric.