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https://issues.apache.org/jira/browse/ZOOKEEPER-3756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17061180#comment-17061180
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Mate Szalay-Beko commented on ZOOKEEPER-3756:
---------------------------------------------

I created a fix, but I am not 100% sure it would solve the problem. I will try 
to come up with some automated test to catch this scenario (injecting timeout 
somehow into the connection creation), but in the meanwhile I share with you a 
patched version: 
[https://drive.google.com/open?id=1qcO-anHIPNn6ipD8nmNAiHmuQD7G4Nvf]  
([https://github.com/symat/zookeeper/commit/d4159aca0d2aea0a544810d3d9b352c10ea55bdf])

This is based on the branch 3.5, I compiled it with OpenJDK 8u242 (I did it on 
Mac, but it shouldn't be a problem).

How easy would be for you to test this version without using the 
{{-Dzookeeper.cnxTimeout=500}} workaround?

If it takes much time, then please wait until I verify the patch on my machine 
(either manually or with automated tests)...

> Members failing to rejoin quorum
> --------------------------------
>
>                 Key: ZOOKEEPER-3756
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3756
>             Project: ZooKeeper
>          Issue Type: Improvement
>          Components: leaderElection
>    Affects Versions: 3.5.6, 3.5.7
>            Reporter: Dai Shi
>            Assignee: Mate Szalay-Beko
>            Priority: Major
>         Attachments: Dockerfile, configmap.yaml, docker-entrypoint.sh, 
> jmx.yaml, zoo-0.log, zoo-1.log, zoo-2.log, zoo-service.yaml, zookeeper.yaml
>
>
> Not sure if this is the place to ask, please close if it's not.
> I am seeing some behavior that I can't explain since upgrading to 3.5:
> In a 5 member quorum, when server 3 is the leader and each server has this in 
> their configuration: 
> {code:java}
> server.1=100.71.255.254:2888:3888:participant;2181
> server.2=100.71.255.253:2888:3888:participant;2181
> server.3=100.71.255.252:2888:3888:participant;2181
> server.4=100.71.255.251:2888:3888:participant;2181
> server.5=100.71.255.250:2888:3888:participant;2181{code}
> If servers 1 or 2 are restarted, they fail to rejoin the quorum with this in 
> the logs:
> {code:java}
> 2020-03-11 20:23:35,720 [myid:2] - INFO  
> [QuorumPeer[myid=2](plain=0.0.0.0:2181)(secure=disabled):QuorumPeer@1175] - 
> LOOKING
> 2020-03-11 20:23:35,721 [myid:2] - INFO  
> [QuorumPeer[myid=2](plain=0.0.0.0:2181)(secure=disabled):FastLeaderElection@885]
>  - New election. My id =  2, proposed zxid=0x1b8005f4bba
> 2020-03-11 20:23:35,733 [myid:2] - INFO  
> [WorkerSender[myid=2]:QuorumCnxManager@438] - Have smaller server identifier, 
> so dropping the connection: (3, 2)
> 2020-03-11 20:23:35,734 [myid:2] - INFO  
> [0.0.0.0/0.0.0.0:3888:QuorumCnxManager$Listener@924] - Received connection 
> request 100.126.116.201:36140
> 2020-03-11 20:23:35,735 [myid:2] - INFO  
> [WorkerSender[myid=2]:QuorumCnxManager@438] - Have smaller server identifier, 
> so dropping the connection: (4, 2)
> 2020-03-11 20:23:35,740 [myid:2] - INFO  
> [WorkerSender[myid=2]:QuorumCnxManager@438] - Have smaller server identifier, 
> so dropping the connection: (5, 2)
> 2020-03-11 20:23:35,740 [myid:2] - INFO  
> [0.0.0.0/0.0.0.0:3888:QuorumCnxManager$Listener@924] - Received connection 
> request 100.126.116.201:36142
> 2020-03-11 20:23:35,740 [myid:2] - INFO  
> [WorkerReceiver[myid=2]:FastLeaderElection@679] - Notification: 2 (message 
> format version), 2 (n.leader), 0x1b8005f4bba (n.zxid), 0x1 (n.round), LOOKING 
> (n.state), 2 (n.sid), 0x1b8 (n.peerEPoch), LOOKING (my state)0 (n.config 
> version)
> 2020-03-11 20:23:35,742 [myid:2] - WARN  
> [SendWorker:3:QuorumCnxManager$SendWorker@1143] - Interrupted while waiting 
> for message on queue
> java.lang.InterruptedException
>         at 
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.reportInterruptAfterWait(AbstractQueuedSynchronizer.java:2014)
>         at 
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2088)
>         at 
> java.util.concurrent.ArrayBlockingQueue.poll(ArrayBlockingQueue.java:418)
>         at 
> org.apache.zookeeper.server.quorum.QuorumCnxManager.pollSendQueue(QuorumCnxManager.java:1294)
>         at 
> org.apache.zookeeper.server.quorum.QuorumCnxManager.access$700(QuorumCnxManager.java:82)
>         at 
> org.apache.zookeeper.server.quorum.QuorumCnxManager$SendWorker.run(QuorumCnxManager.java:1131)
> 2020-03-11 20:23:35,744 [myid:2] - WARN  
> [SendWorker:3:QuorumCnxManager$SendWorker@1153] - Send worker leaving thread  
> id 3 my id = 2
> 2020-03-11 20:23:35,745 [myid:2] - WARN  
> [RecvWorker:3:QuorumCnxManager$RecvWorker@1230] - Interrupting 
> SendWorker{code}
> The only way I can seem to get them to rejoin the quorum is to restart the 
> leader.
> However, if I remove server 4 and 5 from the configuration of server 1 or 2 
> (so only servers 1, 2, and 3 remain in the configuration file), then they can 
> rejoin the quorum fine. Is this expected and am I doing something wrong? Any 
> help or explanation would be greatly appreciated. Thank you.



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