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https://issues.apache.org/jira/browse/HELIX-608?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15586528#comment-15586528
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Haohui Mai commented on HELIX-608:
----------------------------------
I have seen this as well. I found that the callback handlers contain ZooKeeper
clients that have stale connections. They will throw NPE if the handlers are
executed.
I found that Helix does not clear up the callback handlers whenever Helix tries
to reconnect to ZK. What is the best approach to fix it?
> NPE and unable to reconnect to zookeeper after a network outage
> ---------------------------------------------------------------
>
> Key: HELIX-608
> URL: https://issues.apache.org/jira/browse/HELIX-608
> Project: Apache Helix
> Issue Type: Bug
> Components: helix-core
> Affects Versions: 0.7.1
> Reporter: Changgeng Li
>
> I noticed one of the participant is not a live instance in zookeeper after a
> network outage, while the java process is live. I have to restart the java
> process to make it live again.
> Found following logs:
> ERROR 2015-07-28 17:12:15,010 [main-EventThread]
> org.apache.zookeeper.ClientCnxn: Error while calling watcher
> java.lang.RuntimeException: Exception while restarting zk client
> at
> org.I0Itec.zkclient.ZkClient.processStateChanged(ZkClient.java:462)
> ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkClient.process(ZkClient.java:368)
> ~[zaaa.jar:?]
> at
> org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:531)
> [zaaa.jar:?]
> at
> org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:507)
> [zaaa.jar:?]
> Caused by: org.I0Itec.zkclient.exception.ZkException: Unable to connect to
> zzookeeperhost:2181,zookeeperhost2.com:2181/a
> at org.I0Itec.zkclient.ZkConnection.connect(ZkConnection.java:66)
> ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkClient.reconnect(ZkClient.java:935)
> ~[zaaa.jar:?]
> at
> org.I0Itec.zkclient.ZkClient.processStateChanged(ZkClient.java:458)
> ~[zaaa.jar:?]
> ... 3 more
> Caused by: java.net.UnknownHostException: zzookeeperhost: Temporary failure
> in name resolution
> at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
> ~[?:1.7.0_72]
> at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:901)
> ~[?:1.7.0_72]
> at
> java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1293)
> ~[?:1.7.0_72]
> at java.net.InetAddress.getAllByName0(InetAddress.java:1246)
> ~[?:1.7.0_72]
> at java.net.InetAddress.getAllByName(InetAddress.java:1162)
> ~[?:1.7.0_72]
> at java.net.InetAddress.getAllByName(InetAddress.java:1098)
> ~[?:1.7.0_72]
> at org.apache.zookeeper.ClientCnxn.<init>(ClientCnxn.java:387)
> ~[zaaa.jar:?]
> at org.apache.zookeeper.ClientCnxn.<init>(ClientCnxn.java:332)
> ~[zaaa.jar:?]
> at org.apache.zookeeper.ZooKeeper.<init>(ZooKeeper.java:383)
> ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkConnection.connect(ZkConnection.java:64)
> ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkClient.reconnect(ZkClient.java:935)
> ~[zaaa.jar:?]
> at
> org.I0Itec.zkclient.ZkClient.processStateChanged(ZkClient.java:458)
> ~[zaaa.jar:?]
> ... 3 more
> INFO 2015-07-28 17:12:15,010 [main-EventThread]
> org.apache.zookeeper.ClientCnxn: EventThread shut down
> ERROR 2015-07-28 17:12:15,014
> [ZkClient-EventThread-184-zzookeeperhost:2181,zookeeperhost2.com:2181/a]
> org.I0Itec.zkclient.ZkEventThread: Error handling event ZkEvent[Children of
> /zaaa/INSTANCES/10.211.12.21_9000/MESSAGES changed sent to
> org.apache.helix.manager.zk.ZkCallbackHandler@71bd5cfa]
> java.lang.NullPointerException
> at org.I0Itec.zkclient.ZkConnection.exists(ZkConnection.java:95)
> ~[zaaa.jar:?]
> at org.apache.helix.manager.zk.ZkClient$2.call(ZkClient.java:195)
> ~[zaaa.jar:?]
> at org.apache.helix.manager.zk.ZkClient$2.call(ZkClient.java:192)
> ~[zaaa.jar:?]
> at
> org.I0Itec.zkclient.ZkClient.retryUntilConnected(ZkClient.java:675)
> ~[zaaa.jar:?]
> at org.apache.helix.manager.zk.ZkClient.exists(ZkClient.java:192)
> ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkClient.exists(ZkClient.java:445)
> ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkClient$7.run(ZkClient.java:566) ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkEventThread.run(ZkEventThread.java:71)
> [zaaa.jar:?]
> ERROR 2015-07-28 17:12:15,015
> [ZkClient-EventThread-184-zzookeeperhost:2181,zookeeperhost2.com:2181/a]
> org.I0Itec.zkclient.ZkEventThread: Error handling event ZkEvent[Children of
> /zaaa/EXTERNALVIEW changed sent to
> org.apache.helix.manager.zk.ZkCallbackHandler@35d1655]
> java.lang.NullPointerException
> at org.I0Itec.zkclient.ZkConnection.exists(ZkConnection.java:95)
> ~[zaaa.jar:?]
> at org.apache.helix.manager.zk.ZkClient$2.call(ZkClient.java:195)
> ~[zaaa.jar:?]
> at org.apache.helix.manager.zk.ZkClient$2.call(ZkClient.java:192)
> ~[zaaa.jar:?]
> at
> org.I0Itec.zkclient.ZkClient.retryUntilConnected(ZkClient.java:675)
> ~[zaaa.jar:?]
> at org.apache.helix.manager.zk.ZkClient.exists(ZkClient.java:192)
> ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkClient.exists(ZkClient.java:445)
> ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkClient$7.run(ZkClient.java:566) ~[zaaa.jar:?]
> at org.I0Itec.zkclient.ZkEventThread.run(ZkEventThread.java:71)
> [zaaa.jar:?]
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