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https://issues.apache.org/jira/browse/KAFKA-2448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14933489#comment-14933489
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Jun Rao commented on KAFKA-2448:
--------------------------------
[~becket_qin], normally, the firing of the watcher won't be delayed by more
than 10 secs. One thing to be aware of is that ZKClient puts all the fired
watcher events into its own in-memory queue and have a separate thread process
those events in the queue sequentially. The watcher is only re-registered when
the event is processed. So, if when the broker de-registration event is fired,
there are many other events queued up before it, the processing of the
de-registration event may be delayed. By the time it's being processed, the
re-registration may have already happened.
> 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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