private void addMemberSpec(
        Map<String, MemberSubscriptionAndAssignmentImpl> members,
        int memberIndex,
        Set<Uuid> subscribedTopicIds
    ) {
        String memberId = "member" + memberIndex;
        Optional<String> rackId = rackId(memberIndex);

        members.put(memberId, new MemberSubscriptionAndAssignmentImpl(
            rackId,
            Optional.empty(),
            subscribedTopicIds,
            Assignment.EMPTY
        ));
    }
The assignment type is decided based on whether all the members are assigned partitions
for the first time (full), or incrementally when a rebalance is triggered.
jmh-benchmarks/src/main/java/org/apache/kafka/jmh/assignor/ServerSideAssignorBenchmark.java