@Override
    public Iterator<ConsumerRecord<K, V>> iterator() {
        return new ConcatenatedIterable<>(records.values()).iterator();
    }
Get the partitions which have records contained in this record set.
@return the set of partitions with data in this record set (may be empty if no data was returned)
clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerRecords.java