簡介
由于項目中需要使用kafka作為消息隊列斜纪，并且項目是基于spring-boot來進行構建的瓶堕，所以項目采用了spring-kafka作為原生kafka的一個擴展庫進行使用掠河。先說明一下版本：
- spring-boot 的版本是1.4.0.RELEASE
- kafka 的版本是0.9.0.x 版本
- spring-kafka 的版本是1.0.3.RELEASE
用過kafka的人都知道，對于使用kafka來說，producer的使用相對簡單一些奏甫，只需要把數(shù)據(jù)按照指定的格式發(fā)送給kafka中某一個topic就可以了尖飞。本文主要是針對spring-kafka的consumer端上的使用進行簡單一些分析和總結症副。
kafka的速度是很快店雅，所以一般來說producer的生產(chǎn)消息的邏輯速度都會比consumer的消費消息的邏輯速度快。
具體案例
之前在項目中遇到了一個案例是贞铣，consumer消費一條數(shù)據(jù)平均需要200ms的時間闹啦，并且在某個時刻，producer會在短時間內(nèi)產(chǎn)生大量的數(shù)據(jù)丟進kafka的broker里面（假設平均1s中內(nèi)丟入了5w條需要消費的消息辕坝，這個情況會持續(xù)幾分鐘）窍奋。
對于這種情況，kafka的consumer的行為會是：
- kafka的consumer會從broker里面取出一批數(shù)據(jù)酱畅，?給消費線程進行消費琳袄。
- 由于取出的一批消息數(shù)量太大，consumer在
session.timeout.ms時間之內(nèi)沒有消費完成 -
consumer coordinator會由于沒有接受到心跳而掛掉纺酸，并且出現(xiàn)一些日志
[rhllor] Tue Oct 18 21:39:16 CST 2016 INFO [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator coordinatorDead 529: kafka-example|NTI|Marking the coordinator 2147483646 dead.
[rhllor] Tue Oct 18 21:39:16 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator sendGroupMetadataRequest 465: kafka-example|NTI|Issuing group metadata request to broker 1
[rhllor] Tue Oct 18 21:39:16 CST 2016 ERROR [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator handle 550: kafka-example|NTI|Error ILLEGAL_GENERATION occurred while committing offsets for group new-message-1
[rhllor] Tue Oct 18 21:39:16 CST 2016 WARN [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator onComplete 424: kafka-example|NTI|Auto offset commit failed: Commit cannot be completed due to group rebalance
[rhllor] Tue Oct 18 21:39:16 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator run 408: kafka-example|NTI|Cannot auto-commit offsets now since the coordinator is unknown, will retry after backoff
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator handleGroupMetadataResponse 478: kafka-example|NTI|Group metadata response ClientResponse(receivedTimeMs=1476797957072, disconnected=false, request=ClientRequest(expectResponse=true, callback=org.apache.kafka.clients.consumer.internals.ConsumerNetworkClient$RequestFutureCompletionHandler@1d3d7e6, request=RequestSend(header={api_key=10,api_version=0,correlation_id=20,client_id=consumer-1}, body={group_id=new-message-1}), createdTimeMs=1476797956485, sendTimeMs=1476797956485), responseBody={error_code=0,coordinator={node_id=1,host=10.10.44.124,port=9092}})
[rhllor] Tue Oct 18 21:39:17 CST 2016 ERROR [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator handle 550: kafka-example|NTI|Error ILLEGAL_GENERATION occurred while committing offsets for group new-message-1
[rhllor] Tue Oct 18 21:39:17 CST 2016 WARN [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator maybeAutoCommitOffsetsSync 445: kafka-example|NTI|Auto offset commit failed:
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator onJoinPrepare 247: kafka-example|NTI|Revoking previously assigned partitions [rhllor-log-0, rhllor-log-1, rhllor-log-2]
[rhllor] Tue Oct 18 21:39:17 CST 2016 INFO [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.springframework.kafka.listener.KafkaMessageListenerContainer onPartitionsRevoked 244: kafka-example|NTI|partitions revoked:[rhllor-log-0, rhllor-log-1, rhllor-log-2]
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator performGroupJoin 309: kafka-example|NTI|(Re-)joining group new-message-1
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator performGroupJoin 318: kafka-example|NTI|Issuing request (JOIN_GROUP: {group_id=new-message-1,session_timeout=15000,member_id=consumer-1-64063d04-9d4e-45af-a927-17ccf31c6ec1,protocol_type=consumer,group_protocols=[{protocol_name=range,protocol_metadata=java.nio.HeapByteBuffer[pos=0 lim=22 cap=22]}]}) to coordinator 2147483646
[rhllor] Tue Oct 18 21:39:17 CST 2016 INFO [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator handle 354: kafka-example|NTI|Attempt to join group new-message-1 failed due to unknown member id, resetting and retrying.
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator performGroupJoin 309: kafka-example|NTI|(Re-)joining group new-message-1
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator performGroupJoin 318: kafka-example|NTI|Issuing request (JOIN_GROUP: {group_id=new-message-1,session_timeout=15000,member_id=,protocol_type=consumer,group_protocols=[{protocol_name=range,protocol_metadata=java.nio.HeapByteBuffer[pos=0 lim=22 cap=22]}]}) to coordinator 2147483646
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator handle 336: kafka-example|NTI|Joined group: {error_code=0,generation_id=1,group_protocol=range,leader_id=consumer-1-d3f30611-5788-4b81-bf0d-e779a11093d2,member_id=consumer-1-d3f30611-5788-4b81-bf0d-e779a11093d2,members=[{member_id=consumer-1-d3f30611-5788-4b81-bf0d-e779a11093d2,member_metadata=java.nio.HeapByteBuffer[pos=0 lim=22 cap=22]}]}
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator performAssignment 225: kafka-example|NTI|Performing range assignment for subscriptions {consumer-1-d3f30611-5788-4b81-bf0d-e779a11093d2=org.apache.kafka.clients.consumer.internals.PartitionAssignor$Subscription@1dbca7d4}
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator performAssignment 229: kafka-example|NTI|Finished assignment: {consumer-1-d3f30611-5788-4b81-bf0d-e779a11093d2=org.apache.kafka.clients.consumer.internals.PartitionAssignor$Assignment@4826f394}
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator onJoinLeader 397: kafka-example|NTI|Issuing leader SyncGroup (SYNC_GROUP: {group_id=new-message-1,generation_id=1,member_id=consumer-1-d3f30611-5788-4b81-bf0d-e779a11093d2,group_assignment=[{member_id=consumer-1-d3f30611-5788-4b81-bf0d-e779a11093d2,member_assignment=java.nio.HeapByteBuffer[pos=0 lim=38 cap=38]}]}) to coordinator 2147483646
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.AbstractCoordinator handle 423: kafka-example|NTI|Received successful sync group response for group new-message-1: {error_code=0,member_assignment=java.nio.HeapByteBuffer[pos=0 lim=38 cap=38]}
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator onJoinComplete 191: kafka-example|NTI|Setting newly assigned partitions [rhllor-log-0, rhllor-log-1, rhllor-log-2]
[rhllor] Tue Oct 18 21:39:17 CST 2016 INFO [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.springframework.kafka.listener.KafkaMessageListenerContainer onPartitionsAssigned 249: kafka-example|NTI|partitions assigned:[rhllor-log-0, rhllor-log-1, rhllor-log-2]
[rhllor] Tue Oct 18 21:39:17 CST 2016 DEBUG [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-kafka-consumer-1] org.apache.kafka.clients.consumer.internals.ConsumerCoordinator sendOffsetFetchRequest 581: kafka-example|NTI|Fetching committed offsets for partitions: [rhllor-log-0, rhllor-log-1, rhllor-log-2]
日志的意思大概是coordinator掛掉了窖逗，然后自動提交offset失敗，然后重新分配partition給客戶端
- 由于自動提交offset失敗餐蔬，導致重新分配了partition的客戶端又重新消費之前的一批數(shù)據(jù)
- 接著consumer重新消費碎紊，又出現(xiàn)了消費超時，無限循環(huán)下去用含。
解決方案
遇到了這個問題之后矮慕， 我們做了一些步驟：
- 提高了partition的數(shù)量，從而提高了consumer的并行能力啄骇，從而提高數(shù)據(jù)的消費能力
- ?對于單partition的消費線程痴鳄，增加了一個固定長度的阻塞隊列和工作線程池進一步提高并行消費的能力
- ?由于使用了spring-kafka，則把kafka-client的
enable.auto.commit設置成了false缸夹，表示禁止kafka-client自動提交offset痪寻，因為就是之前的自動提交失敗，導致offset永遠沒更新虽惭，從而轉(zhuǎn)向使用spring-kafka的offset提交機制橡类。并且spring-kafka提供了多種提交策略：
/**
* The ack mode to use when auto ack (in the configuration properties) is false.
* <ul>
* <li>RECORD: Ack after each record has been passed to the listener.</li>
* <li>BATCH: Ack after each batch of records received from the consumer has been
* passed to the listener</li>
* <li>TIME: Ack after this number of milliseconds; (should be greater than
* {@code #setPollTimeout(long) pollTimeout}.</li>
* <li>COUNT: Ack after at least this number of records have been received</li>
* <li>MANUAL: Listener is responsible for acking - use a
* {@link AcknowledgingMessageListener}.
* </ul>
*/
private AbstractMessageListenerContainer.AckMode ackMode = AckMode.BATCH;
這些策略保證了在一批消息沒有完成消費的情況下，也能提交offset芽唇，從而避免了完全提交不上而導致永遠重復消費的問題顾画。
分析
那么問題來了，為什么spring-kafka的提交offset的策略能夠解決spring-kafka的auto-commit的帶來的重復消費的問題呢匆笤？下面通過分析spring-kafka的關鍵源碼來解析這個問題研侣。
- 首先來看看spring-kafka的消費線程邏輯
if (isRunning() && this.definedPartitions != null) {
initPartitionsIfNeeded();
// we start the invoker here as there will be no rebalance calls to
// trigger it, but only if the container is not set to autocommit
// otherwise we will process records on a separate thread
if (!this.autoCommit) {
startInvoker();
}
}
上面可以看到，如果auto.commit關掉的話炮捧，spring-kafka會啟動一個invoker庶诡，這個invoker的目的就是啟動一個線程去消費數(shù)據(jù)，他消費的數(shù)據(jù)不是直接從kafka里面直接取的咆课，那么他消費的數(shù)據(jù)從哪里來呢末誓？他是從一個spring-kafka自己創(chuàng)建的阻塞隊列里面取的扯俱。
然后會進入一個循環(huán)，從源代碼中可以看到如果
auto.commit被關掉的話喇澡， 他會先把之前處理過的數(shù)據(jù)先進行提交offset迅栅，然后再去從kafka里面取數(shù)據(jù)。然后把取到的數(shù)據(jù)丟給上面提到的阻塞列隊晴玖，由上面創(chuàng)建的線程去消費库继，并且如果阻塞隊列滿了導致取到的數(shù)據(jù)塞不進去的話，spring-kafka會調(diào)用kafka的pause方法窜醉，則consumer會停止從kafka里面繼續(xù)再拿數(shù)據(jù)宪萄。
接著spring-kafka還會處理一些異常的情況，比如失敗之后是不是需要commit offset這樣的邏輯榨惰。
最后
- spring-kafka是一個很好的用來操作kafka的庫拜英，并且可以和spring進行完美結合。
- spring-kafka提供了一些kafka使用上功能的擴展琅催。
- 相比于使用原生的kafka-client的api的話居凶，使用更加簡單，需要編寫的碼量更少藤抡。
- 最好能夠使用最新的kafka（0.10.0）和spring-kafka（1.1.1.RELEASE）的版本
