我不能给你一个确切的答案，但我发现它很有趣，足以检验它。
为此，我创建了一个包含四个分区的主题，并使用 kafka-producer-perf-test 命令行工具生成一些消息到主题中。由于性能测试工具根本不会创建任何键，因此消息以循环方式写入主题分区。

kafka-producer-perf-test --topic test --num-records 1337 --throughput -1 --record-size 128 --producer-props key.serializer=org.apache.kafka.common.serialization.StringSerializer --producer-props value.serializer=org.apache.kafka.common.serialization.StringSerializer --producer-props bootstrap.servers=localhost:9092

之后，我使用配置创建了一个简单的kafkaconsumer max_poll_records=5 来配合你的问题。使用者只需打印出消耗的每条消息的偏移量和分区：

Integer counter = 0;

// consume messages with `poll` call and print out results
try(KafkaConsumer<String, String> consumer = new KafkaConsumer<String, String>(settings)) {
    consumer.subscribe(Arrays.asList(topic));
    while (true) {
        System.out.printf("Batch = %d\n", counter);
        ConsumerRecords<String, String> records = consumer.poll(Duration.ofMillis(100));
        for (ConsumerRecord<String, String> record : records) {
            System.out.printf("offset = %d, partition = %d\n", record.offset(), record.partition());
        }
        counter += 1;
    }
}

回答您的问题的结果是，使用者在移动到另一个分区之前尝试从一个分区获取尽可能多的数据。仅在所有来自分区的消息 1 已消耗，但未达到最大轮询记录数5的限制，但它又从分区添加了两条消息 2 .
以下是一些指纹，以便更好地理解。

Batch = 0
offset = 310, partition = 0
offset = 311, partition = 0
offset = 312, partition = 0
offset = 313, partition = 0
offset = 314, partition = 0

Batch = 1
offset = 315, partition = 0
offset = 316, partition = 0
offset = 317, partition = 0
offset = 318, partition = 0
offset = 319, partition = 0

# only offsets with partition 0

Batch = 45
offset = 525, partition = 0
offset = 526, partition = 0
offset = 527, partition = 0
offset = 528, partition = 0
offset = 529, partition = 0
Batch = 46
offset = 728, partition = 1
offset = 729, partition = 1
offset = 730, partition = 1
offset = 731, partition = 1
offset = 732, partition = 1

# only offsets with partition 1

Batch = 86
offset = 928, partition = 1
offset = 929, partition = 1
offset = 930, partition = 1
offset = 931, partition = 1
offset = 932, partition = 1
Batch = 87
offset = 465, partition = 2
offset = 466, partition = 2
offset = 933, partition = 1
offset = 934, partition = 1
offset = 935, partition = 1
Batch = 88
offset = 467, partition = 2
offset = 468, partition = 2
offset = 469, partition = 2
offset = 470, partition = 2
offset = 471, partition = 2

## and so on