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https://issues.apache.org/jira/browse/HBASE-5549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13440074#comment-13440074
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stack commented on HBASE-5549:
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@Himanshu A thread dump when its hung? Might tell us something?
@Lars Done I'm triggering and watching 0.94 builds... will make sure I've not
added a regression.
> Master can fail if ZooKeeper session expires
> --------------------------------------------
>
> Key: HBASE-5549
> URL: https://issues.apache.org/jira/browse/HBASE-5549
> Project: HBase
> Issue Type: Bug
> Components: master, zookeeper
> Affects Versions: 0.96.0
> Environment: all
> Reporter: nkeywal
> Assignee: nkeywal
> Priority: Minor
> Fix For: 0.92.2, 0.96.0, 0.94.2
>
> Attachments: 5549_092.txt, 5549_094.txt, 5549.v10.patch,
> 5549.v11.patch, 5549.v6.patch, 5549.v7.patch, 5549.v8.patch, 5549.v9.patch,
> nochange.patch
>
>
> There is a retry mechanism in RecoverableZooKeeper, but when the session
> expires, the whole ZooKeeperWatcher is recreated, hence the retry mechanism
> does not work in this case. This is why a sleep is needed in
> TestZooKeeper#testMasterSessionExpired: we need to wait for ZooKeeperWatcher
> to be recreated before using the connection.
> This can happen in real life, it can happen when:
> - master & zookeeper starts
> - zookeeper connection is cut
> - master enters the retry loop
> - in the meantime the session expires
> - the network comes back, the session is recreated
> - the retries continues, but on the wrong object, hence fails.
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