private Optional<String> rackId(int memberIndex) {
        return isRackAware ? Optional.of("rack" + memberIndex % NUMBER_OF_RACKS) : Optional.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