private TopicPartition getTheActualPartitionToBeMoved(TopicPartition partition, String oldConsumer, String newConsumer) {
            String topic = partition.topic();

            if (!partitionMovementsByTopic.containsKey(topic))
                return partition;

            if (partitionMovements.containsKey(partition)) {
                // this partition has previously moved
                assert oldConsumer.equals(partitionMovements.get(partition).dstMemberId);
                oldConsumer = partitionMovements.get(partition).srcMemberId;
            }

            Map<ConsumerPair, Set<TopicPartition>> partitionMovementsForThisTopic = partitionMovementsByTopic.get(topic);
            ConsumerPair reversePair = new ConsumerPair(newConsumer, oldConsumer);
            if (!partitionMovementsForThisTopic.containsKey(reversePair))
                return partition;

            return partitionMovementsForThisTopic.get(reversePair).iterator().next();
        }
This class maintains some data structures to simplify lookup of partition movements among consumers. At each point of
time during a partition rebalance it keeps track of partition movements corresponding to each topic, and also possible
movement (in form a <code>ConsumerPair</code> object) for each partition.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/AbstractStickyAssignor.java