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Posted to dev@kafka.apache.org by "Jun Rao (JIRA)" <ji...@apache.org> on 2015/09/26 01:15:04 UTC
[jira] [Commented] (KAFKA-2448) BrokerChangeListener missed broker
id path ephemeral node deletion event.
[ https://issues.apache.org/jira/browse/KAFKA-2448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14908857#comment-14908857 ]
Jun Rao commented on KAFKA-2448:
--------------------------------
[~becket_qin], since ZK watchers are one-time watchers, currently, we have the following bug in the controller. If a broker is stopped and restarted very quickly, it can happen that the broker deregistration triggers a ZK event, but by the time the controller reads the broker path, the broker is registered in ZK again. Currently, the controller just treats this as if there is no broker change and doesn't do anything, which is incorrect. One way to fix this is to remember the zk version of the broker registration in the controller. When processing a broker registration change event, we read every broker's registration in ZK and compares its current ZK version with the one cached in the controller. If the ZK version has changed, we know the broker has gone and come back and can act accordingly. This does have the overhead of requiring the controller to read all broker registrations. Perhaps [~fpj] can comment if there is a more efficient way of doing this.
> BrokerChangeListener missed broker id path ephemeral node deletion event.
> -------------------------------------------------------------------------
>
> Key: KAFKA-2448
> URL: https://issues.apache.org/jira/browse/KAFKA-2448
> Project: Kafka
> Issue Type: Bug
> Reporter: Jiangjie Qin
> Assignee: Flavio Junqueira
> Fix For: 0.9.0.0
>
>
> When a broker get bounced, ideally the sequence should be like this:
> 1.1. Broker shutdown resources.
> 1.2. Broker close zkClient (this will cause the ephemeral node of /brokers/ids/BROKER_ID to be deleted)
> 1.3. Broker restart and load the log segment
> 1.4. Broker create ephemeral node /brokers/ids/BROKER_ID
> The broker side log s are:
> {noformat}
> ...
> 2015/08/17 22:42:37.663 INFO [SocketServer] [Thread-1] [kafka-server] [] [Socket Server on Broker 1140], Shutting down
> 2015/08/17 22:42:37.735 INFO [SocketServer] [Thread-1] [kafka-server] [] [Socket Server on Broker 1140], Shutdown completed
> ...
> 2015/08/17 22:42:53.898 INFO [ZooKeeper] [Thread-1] [kafka-server] [] Session: 0x14d43fd905f68d7 closed
> 2015/08/17 22:42:53.898 INFO [ClientCnxn] [main-EventThread] [kafka-server] [] EventThread shut down
> 2015/08/17 22:42:53.898 INFO [KafkaServer] [Thread-1] [kafka-server] [] [Kafka Server 1140], shut down completed
> ...
> 2015/08/17 22:43:03.306 INFO [ClientCnxn] [main-SendThread(zk-ei1-kafkatest.stg.linkedin.com:12913)] [kafka-server] [] Session establishment complete on server zk-ei1-kafkatest.stg.linkedin
> .com/172.20.73.211:12913, sessionid = 0x24d43fd93d96821, negotiated timeout = 12000
> 2015/08/17 22:43:03.306 INFO [ZkClient] [main-EventThread] [kafka-server] [] zookeeper state changed (SyncConnected)
> ...
> {noformat}
> On the controller side, the sequence should be:
> 2.1. Controlled shutdown the broker
> 2.2. BrokerChangeListener fired for /brokers/ids child change because ephemeral node is deleted in step 1.2
> 2.3. BrokerChangeListener fired again for /borkers/ids child change because the ephemeral node is created in 1.4
> The issue I saw was on controller side, the broker change listener only fired once after step 1.4. So the controller did not see any broker change.
> {noformat}
> 2015/08/17 22:41:46.189 [KafkaController] [Controller 1507]: Shutting down broker 1140
> ...
> 2015/08/17 22:42:38.031 [RequestSendThread] [Controller-1507-to-broker-1140-send-thread], Controller 1507 epoch 799 fails to send request Name: StopReplicaRequest; Version: 0; CorrelationId: 5334; ClientId: ; DeletePartitions: false; ControllerId: 1507; ControllerEpoch: 799; Partitions: [seas-decisionboard-searcher-service_call,1] to broker 1140 : (EndPoint(eat1-app1140.corp.linkedin.com,10251,PLAINTEXT)). Reconnecting to broker.
> java.nio.channels.ClosedChannelException
> at kafka.network.BlockingChannel.send(BlockingChannel.scala:110)
> at kafka.controller.RequestSendThread.liftedTree1$1(ControllerChannelManager.scala:132)
> at kafka.controller.RequestSendThread.doWork(ControllerChannelManager.scala:131)
> at kafka.utils.ShutdownableThread.run(ShutdownableThread.scala:60)
> 2015/08/17 22:42:38.031 [RequestSendThread] [Controller-1507-to-broker-1140-send-thread], Controller 1507 connected to 1140 : (EndPoint(eat1-app1140.corp.linkedin.com,10251,PLAINTEXT)) for sending state change requests
> 2015/08/17 22:42:38.332 [RequestSendThread] [Controller-1507-to-broker-1140-send-thread], Controller 1507 epoch 799 fails to send request Name: StopReplicaRequest; Version: 0; CorrelationId: 5334; ClientId: ; DeletePartitions: false; ControllerId: 1507; ControllerEpoch: 799; Partitions: [seas-decisionboard-searcher-service_call,1] to broker 1140 : (EndPoint(eat1-app1140.corp.linkedin.com,10251,PLAINTEXT)). Reconnecting to broker.
> java.nio.channels.ClosedChannelException
> at kafka.network.BlockingChannel.send(BlockingChannel.scala:110)
> at kafka.controller.RequestSendThread.liftedTree1$1(ControllerChannelManager.scala:132)
> at kafka.controller.RequestSendThread.doWork(ControllerChannelManager.scala:131)
> at kafka.utils.ShutdownableThread.run(ShutdownableThread.scala:60)
> ....
> 2015/08/17 22:43:09.035 [ReplicaStateMachine$BrokerChangeListener] [BrokerChangeListener on Controller 1507]: Broker change listener fired for path /brokers/ids with children 1140,1282,1579,871,1556,872,1511,873,874,852,1575,875,1574,1530,854,857,858,859,1493,1272,880,1547,1568,1500,1521,863,864,865,867,1507
> 2015/08/17 22:43:09.082 [ReplicaStateMachine$BrokerChangeListener] [BrokerChangeListener on Controller 1507]: Newly added brokers: , deleted brokers: , all live brokers: 873,1507,1511,1568,1521,852,874,857,1493,1530,875,1282,1574,880,863,858,1556,1547,872,1579,864,1272,859,1575,854,867,865,1500,871
> {noformat}
> From ZK transaction log, the zk session in step 1.4 has already be closed.
> {noformat}
> 2015-08-17T22:42:53.899Z, s:0x14d43fd905f68d7, zx:0x26088e0cda UNKNOWN(null)
> {noformat}
> In this case, there are 10 seconds between step 1.2 and step 1.4
> ZK session timeout was set to 12 seconds.
> According to our test, the ephemeral node in zookeeper will be deleted after the session is explicitly closed. But it seems not the case when the broker shuts down.
> Another suspicious thing is that even after socket server one broker has shutdown, the controller was still be able to connect to the broker and send request.
> Currently we are setting the zk session timeout to 6 seconds and this seems solve the problem. My hunch is that zookeeper somehow did not fire the callback in step 1.2. So step 2.2 was not triggered.
> From the available log, the missing piece here is how do we know if the zk watcher has been fired by zookeeper in step 2.2?
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