private ConsumerPair removeMovementRecordOfPartition(TopicPartition partition) {
            ConsumerPair pair = partitionMovements.remove(partition);

            String topic = partition.topic();
            Map<ConsumerPair, Set<TopicPartition>> partitionMovementsForThisTopic = partitionMovementsByTopic.get(topic);
            partitionMovementsForThisTopic.get(pair).remove(partition);
            if (partitionMovementsForThisTopic.get(pair).isEmpty())
                partitionMovementsForThisTopic.remove(pair);
            if (partitionMovementsByTopic.get(topic).isEmpty())
                partitionMovementsByTopic.remove(topic);

            return pair;
        }
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