异常
org.apache.kafka.clients.consumer.CommitFailedException: Commit cannot be completed since the group has already rebalanced and assigned the partitions to another member. This means that the time between subsequent calls to poll() was longer than the configured max.poll.interval.ms, which typically implies that the poll loop is spending too much time message processing. You can address this either by increasing the session timeout or by reducing the maximum size of batches returned in poll() with max.poll.records. at org.apache.kafka.clients.consumer.internals.ConsumerCoordinator$OffsetCommitResponseHandler.handle(ConsumerCoordinator.java:775) at org.apache.kafka.clients.consumer.internals.ConsumerCoordinator$OffsetCommitResponseHandler.handle(ConsumerCoordinator.java:726)
异常的主要信息：
a) CommitFailedException
b) Commit cannot be completed since the group has already rebalanced and assigned the partitions to another member. This means that the time between subsequent calls to poll() was longer than the configured max.poll.interval.ms, which typically implies that the poll loop is spending too much time message processing. You can address this either by increasing the session timeout or by reducing the maximum size of batches returned in poll() with max.poll.records.
其实如果我们对其中的参数，或是对消费的机制比较了解，这个问题就很好解决。当我看到这个异常，我很开心，因为我知道我能通过此异常了解一下Kafka Consumer 消费消息的大致过程。心态是好的~~~
其实现在看这个异常是说：该Consumer不能提交offset了，因为它已经出局了，是因为你的处理小时时间长于你要报告给server的时间。同时还告诉我们怎么处理：要么增加超时时间，要么减少每次poll回来的消息个数。
主要问题在于，何为session timeout？maximum size of batches？poll(timeout)中timeout什么意思？
处理过程
a) 找官网doc
版本：1.1.0
有效信息：
换成通俗易懂的人话：
poll() API 主要是判断consumer是否还活着，只要我们持续调用poll()，消费者就会存活在自己所在的group中，并且持续的消费指定partition的消息。底层是这么做的：消费者向server持续发送心跳，如果一个时间段（session.timeout.ms）consumer挂掉或是不能发送心跳，这个消费者会被认为是挂掉了，这个Partition也会被重新分配给其他consumer
下边这个例子如果理解不上，请通读全文后，再回来理解一下笔者的意思
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背景：你是个搬砖的，同时还是个瓦工，en….你还有个儿子
上述错误就是：工头命令每个码农（consumer）最多10分钟把一个100块转运到目的地并把搬来的砖垒房子，然后回来接着取砖、垒房子。问题在于，你搬了100块砖走了，但是10分钟过去了，你还没回来，那我怎么知道你是不是偷懒睡觉去了，工头就把这个搬砖垒房子的活分给同在一起干活的其他人了（同group不同consumer）。其实你可能没有偷懒，是因为你太追求完美了（估计是处女座，或是垒自家的房子），垒房子的时间很长（spending too much time message processing），10分钟内没能回来向工头报道，这时，你就得和工头商量，两种办法：1、能不能15分钟内回来就行，2、10分钟内回来，但每次搬80块砖来垒房子。
如果老板是个比较有控制欲的人，对于第二中办法，同样的工作量，你无非是多跑几趟。还能很好的控制你；但是对于第一种办法，老板是不愿意的，为什么，因为和你一起搬砖的还有其他人，他可以协调（rebalance）其他5分钟就回来的人来干你的活。你告诉他15分钟对于工头来说是相对不可控的。
当然你还有两位一种办法，你可以找你儿子来搬砖（另起一个线程），你来垒房子，等你垒完了100块转，你儿子去告诉工头，并搬回下一个100块转。但是要注意有一个问题，就是你儿子不能在你还没有垒完上一个100块转前就报告给工头，去获取下一批100块转。这样你就处理不过来了。
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通过上边的例子，我们大致清楚了max.poll.interval.ms？maximum size of batches？
max.poll.interval.ms：消费者最大心跳时间间隔
maximum size of batches：消费者每次获取消息的个数
什么时候发送心跳呢？是poll()方法被调用发送心跳吗？那poll(timeout)中timeout是什么意思呢？
官网对poll(timeout)中timeout的解释如下：
Parameters: timeout - The time, in milliseconds, spent waiting in poll if data is not available in the buffer. If 0, returns immediately with any records that are available currently in the buffer, else returns empty. Must not be negative.
这个我费了很大力气都没有给它翻译成人话……
怎么办？看源码？大致看了下，但是水平有限。。。真的不知道什么时候发送心跳。那就剩下最后一招了（杀手锏）---写例子验证
验证
1、producer
public class ProducerTest {
@Test
public void TestPro() {
Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("acks", "all");
props.put("retries", 0);
props.put("batch.size", 16384);
props.put("linger.ms", 1);
props.put("buffer.memory", 33554432);
props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");
Producer<String, String> producer = new KafkaProducer<String, String>(props);
for (int i = 0; i < 30; i++)
producer.send(new ProducerRecord<String, String>("user_behavior", Integer.toString(i), "hello-"+i));
producer.close();
}
}
2、consumer
public class ConsumerTest {
@Test
public void TestCon() throws InterruptedException {
Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("group.id", "test");
props.put("enable.auto.commit", "false");
props.put("auto.offset.reset", "earliest");
props.put("max.poll.records", 5);
props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
KafkaConsumer<String, String> consumer = new KafkaConsumer<String, String>(props);
consumer.subscribe(Arrays.asList("user_behavior"));
int i = 0;
while (true) {
ConsumerRecords<String, String> records = consumer.poll(3000);
System.out.println("polls out: " + ++i + "time: " + KafkaHelper.timestmp2date(System.currentTimeMillis()));
for (ConsumerRecord<String, String> record : records) {
System.out.printf("time = %s, partition = %s, offset = %d, key = %s, value = %s%n",
KafkaHelper.timestmp2date(record.timestamp()),
record.partition(),
record.offset(),
record.key(),
record.value());
}
consumer.commitSync();
}
}
}
a）测试poll中的参数作用
直接启动Consumer打印结果：
polls out: 1time: 2018-06-13 15:25:19 polls out: 2time: 2018-06-13 15:25:22 polls out: 3time: 2018-06-13 15:25:25 polls out: 4time: 2018-06-13 15:25:28
一开始我错误以为：这个timeout是Consumer每次拉去消息的时间间隔
但我启动了Producer后，打印结果：
polls out: 1time: 2018-06-13 15:27:40 polls out: 2time: 2018-06-13 15:27:43 polls out: 3time: 2018-06-13 15:27:46 polls out: 4time: 2018-06-13 15:27:49 polls out: 5time: 2018-06-13 15:27:52 time = 2018-06-13 15:27:52, partition = 0, offset = 503, key = 1, value = hello-1 time = 2018-06-13 15:27:52, partition = 0, offset = 504, key = 5, value = hello-5 polls out: 6time: 2018-06-13 15:27:52 time = 2018-06-13 15:27:52, partition = 1, offset = 157, key = 4, value = hello-4 time = 2018-06-13 15:27:52, partition = 2, offset = 129, key = 0, value = hello-0 time = 2018-06-13 15:27:52, partition = 2, offset = 130, key = 2, value = hello-2 time = 2018-06-13 15:27:52, partition = 2, offset = 131, key = 3, value = hello-3 polls out: 7time: 2018-06-13 15:27:55 polls out: 8time: 2018-06-13 15:27:58 polls out: 9time: 2018-06-13 15:28:01 polls out: 10time: 2018-06-13 15:28:04
由此可见，第5次和第6次调用poll方法的时间相同。
至此，结合官网的描述对poll(timeout) 的timeout参数认识如下
如果消息队列中没有消息，等待timeout毫秒后，调用poll()方法。如果队列中有消息，立即消费消息，每次消费的消息的多少可以通过max.poll.records配置。
b）测试max.poll.interval.ms
public class ConsumerTest {
@Test
public void TestCon() throws InterruptedException {
Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("group.id", "test");
props.put("enable.auto.commit", "false");
props.put("auto.offset.reset", "earliest");
props.put("max.poll.records", 5);
props.put(ConsumerConfig.MAX_POLL_INTERVAL_MS_CONFIG, "1000");
props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
KafkaConsumer<String, String> consumer = new KafkaConsumer<String, String>(props);
consumer.subscribe(Arrays.asList("user_behavior"));
int i = 0;
while (true) {
ConsumerRecords<String, String> records = consumer.poll(3000);
System.out.println("polls out: " + ++i + "time: " + KafkaHelper.timestmp2date(System.currentTimeMillis()));
for (ConsumerRecord<String, String> record : records) {
System.out.printf("time = %s, partition = %s, offset = %d, key = %s, value = %s%n",
KafkaHelper.timestmp2date(record.timestamp()),
record.partition(),
record.offset(),
record.key(),
record.value());
}
consumer.commitSync();
}
}
}
启动Consumer、Producer运行正常不报错
polls out: 1time: 2018-06-13 15:53:07 polls out: 2time: 2018-06-13 15:53:07 time = 2018-06-13 15:53:07, partition = 1, offset = 158, key = 4, value = hello-4 time = 2018-06-13 15:53:07, partition = 0, offset = 505, key = 1, value = hello-1 time = 2018-06-13 15:53:07, partition = 0, offset = 506, key = 5, value = hello-5 time = 2018-06-13 15:53:07, partition = 2, offset = 132, key = 0, value = hello-0 time = 2018-06-13 15:53:07, partition = 2, offset = 133, key = 2, value = hello-2 polls out: 3time: 2018-06-13 15:53:07 time = 2018-06-13 15:53:07, partition = 2, offset = 134, key = 3, value = hello-3 polls out: 4time: 2018-06-13 15:53:10 polls out: 5time: 2018-06-13 15:53:13
想到异常里提到的处理消息时间过长（spending too much time message processing）
Consumer代码增加处理时间
public class ConsumerTest {
@Test
public void TestCon() throws InterruptedException {
Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("group.id", "test");
props.put("enable.auto.commit", "false");
props.put("auto.offset.reset", "earliest");
props.put("max.poll.records", 5);
props.put(ConsumerConfig.MAX_POLL_INTERVAL_MS_CONFIG, "1000");
props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
KafkaConsumer<String, String> consumer = new KafkaConsumer<String, String>(props);
consumer.subscribe(Arrays.asList("user_behavior"));
int i = 0;
while (true) {
ConsumerRecords<String, String> records = consumer.poll(3000);
System.out.println("polls out: " + ++i + "time: " + KafkaHelper.timestmp2date(System.currentTimeMillis()));
for (ConsumerRecord<String, String> record : records) {
System.out.printf("time = %s, partition = %s, offset = %d, key = %s, value = %s%n",
KafkaHelper.timestmp2date(record.timestamp()),
record.partition(),
record.offset(),
record.key(),
record.value());
TimeUnit.SECONDS.sleep(2);
}
consumer.commitSync();
}
}
}
polls out: 1time: 2018-06-13 15:59:13 polls out: 2time: 2018-06-13 15:59:16 polls out: 3time: 2018-06-13 15:59:19 polls out: 4time: 2018-06-13 15:59:22 polls out: 5time: 2018-06-13 15:59:22 time = 2018-06-13 15:59:22, partition = 2, offset = 135, key = 0, value = hello-0 time = 2018-06-13 15:59:22, partition = 2, offset = 136, key = 2, value = hello-2 time = 2018-06-13 15:59:22, partition = 2, offset = 137, key = 3, value = hello-3 org.apache.kafka.clients.consumer.CommitFailedException: Commit cannot be completed since the group has already rebalanced and assigned the partitions to another member. This means that the time between subsequent calls to poll() was longer than the configured max.poll.interval.ms, which typically implies that the poll loop is spending too much time message processing. You can address this either by increasing the session timeout or by reducing the maximum size of batches returned in poll() with max.poll.records. at org.apache.kafka.clients.consumer.internals.ConsumerCoordinator.sendOffsetCommitRequest(ConsumerCoordinator.java:713) at org.apache.kafka.clients.consumer.internals.ConsumerCoordinator.commitOffsetsSync(ConsumerCoordinator.java:596) ...
久违的异常终于出现了
至此可以看出max.poll.interval.ms是获取消息后，处理这些消息所用时间不能超过该值。即：两次poll的时间间隔最大时间
那么对于何时发送心跳想必也是在调用poll(timeout)方法的时候发送的（猜测），因为超过了max.poll.interval,ms后，这个consumer就被视为挂了。
ps:sleep时间改为0.5秒也会抛异常，因为每次poll5条消息，处理时间2.5s>max.poll.interval,ms=1000ms
异常解决
a)调大max.poll.interval,ms，默认300000（300s）
b)调小max.poll.records，默认500
c)另起线程
后续：
写一个单独处理的message的线程，这样消费和处理分开就不会出现此异常。但要注意处理完一批消息后才能提交offset，然后进行下次的poll（会用到CountDownLatch）
总结：
遇到Exception要淡定，每个Exception搞清楚缘由后都是一次提高的过程。
Ps: 代码中包含<strong>标签是因为我想在更改出加粗，生成后就多了<strong>标签了。