code: def _select_broker_pair(self, rg_destination, victim_partition):
          
          broker_source = self._elect_source_broker(victim_partition)
          broker_destination = rg_destination._elect_dest_broker(victim_partition)
          return broker_source, broker_destination
docs: Select best-fit source and destination brokers based on partition
          count and presence of partition over the broker.
  
          * Get overloaded and underloaded brokers
          Best-fit Selection Criteria:
          Source broker: Select broker containing the victim-partition with
          maximum partitions.
          Destination broker: NOT containing the victim-partition with minimum
          partitions. If no such broker found, return first broker.
  
          This helps in ensuring:-
          * Topic-partitions are distributed across brokers.
          * Partition-count is balanced across replication-groups.