@Override
        public String toString() {
            return "NextTransactionalIdHint["
                    + "lastParallelism="
                    + lastParallelism
                    + ", nextFreeTransactionalId="
                    + nextFreeTransactionalId
                    + ']';
        }
Keep information required to deduce next safe to use transactional id.
inlong-sort/sort-flink/sort-flink-v1.13/sort-connectors/kafka/src/main/java/org/apache/inlong/sort/kafka/FlinkKafkaProducer.java