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https://issues.apache.org/jira/browse/HIVE-24713?focusedWorklogId=545193&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-545193
]
ASF GitHub Bot logged work on HIVE-24713:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 01/Feb/21 09:26
Start Date: 01/Feb/21 09:26
Worklog Time Spent: 10m
Work Description: EugeneChung opened a new pull request #1932:
URL: https://github.com/apache/hive/pull/1932
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Register ZKDeRegisterWatcher again for NodeDataChanged event after ZK
connection reestablishment
### Why are the changes needed?
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It's a bug. After ZK connection is reestablished, NodeDataChanged event for
the server node is occurred. Then it is never notified again. HS2 eventually
never knows deregistering from Zookeeper.
### Does this PR introduce _any_ user-facing change?
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No
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On my company's environment. I described reproduction process of the problem
on the ticket.
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Issue Time Tracking
-------------------
Worklog Id: (was: 545193)
Remaining Estimate: 0h
Time Spent: 10m
> HS2 never knows the deregistering from Zookeeper in the particular case
> -----------------------------------------------------------------------
>
> Key: HIVE-24713
> URL: https://issues.apache.org/jira/browse/HIVE-24713
> Project: Hive
> Issue Type: Bug
> Components: HiveServer2
> Reporter: Eugene Chung
> Assignee: Eugene Chung
> Priority: Major
> Fix For: 4.0.0
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> While using zookeeper discovery mode, the problem that HS2 never knows
> deregistering from Zookeeper could always happen.
> Reproduction is simple.
> # Find one of the zk servers which holds the DeRegisterWatcher watches of
> HS2 instances. If the version of ZK server is 3.5.0 or above, it's easily
> found with [http://zk-server:8080/commands/watches] (ZK AdminServer feature)
> # Check which HS2 instance is watching on the ZK server found at 1, say it's
> _hs2-of-2_
> # Restart the ZK server found at 1
> # Deregister _hs2-of-2_ with the command
> {noformat}
> hive --service hiveserver2 -deregister hs2-of-2{noformat}
> # _hs2-of-2_ never knows that it must be shut down because the watch event
> of DeregisterWatcher was already fired at the time of 3.
> The reason of the problem is explained at
> [https://zookeeper.apache.org/doc/r3.3.3/zookeeperProgrammers.html#sc_WatchRememberThese]
> I added some logging to DeRegisterWatcher and checked what events were
> occurred at the time of 3(restarting of ZK server);
> # WatchedEvent state:Disconnected type:None path:null
> # WatchedEvent[WatchedEvent state:SyncConnected type:None path:null]
> # WatchedEvent[WatchedEvent state:SaslAuthenticated type:None path:null]
> # WatchedEvent[WatchedEvent state:SyncConnected type:NodeDataChanged
> path:/hiveserver2/serverUri=hs2-of-2:10000;version=3.1.2;sequence=0000000711]
> As the zk manual says, watches are one-time triggers. When the connection to
> the ZK server was reestablished, state:SyncConnected
> type:NodeDataChanged,path:hs2-of-2 was fired and it's the end.
> *DeregisterWatcher must be registered again for the same znode to get a
> future NodeDeleted event.*
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