private String generateRemoteReplicaMetricPrefix(RemoteReplicaInfo remoteReplicaInfo) {
    ReplicaId replicaId = remoteReplicaInfo.getReplicaId();
    DataNodeId dataNodeId = replicaId.getDataNodeId();
    return dataNodeId.getHostname() + "-" + dataNodeId.getPort() + "-" + replicaId.getPartitionId().toString();
  }
Get tha average replication lag of remote replicas in given datacenter
@param dcName the name of dc where remote replicas sit
@return the average replication lag
ambry-replication/src/main/java/com/github/ambry/replication/ReplicationMetrics.java