kafka 0.10中的多个线程

Question

在kafka 0.8.2中，我们可以明确定义处理多分区的线程数，但在kafka 0.10中，例如：

for (TopicPartition partition : records.partitions()) { //按partition处理
    List<ConsumerRecord<String, String>> partitionRecords = records.records(partition); //取出partition对应的Records
    for (ConsumerRecord<String, String> record : partitionRecords) {
        System.out.printf("partition = %d, offset = %d, key = %s, value = %s",record.partition(), record.offset(), record.key(), record.value());
     }
     // consumer.commitSync();
     long lastOffset = partitionRecords.get(partitionRecords.size() - 1).offset(); //取出last offset
     consumer.commitSync(Collections.singletonMap(partition, new OffsetAndMetadata(lastOffset + 1))); //独立的sync每个partition的offset
 }

以这种方式，它如何处理多分区？单线程还是其他？