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Date: Fri, 24 Aug 2012 01:52:42 +1100 (NCT)
From: "Himanshu Vashishtha (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-5549) Master can fail if ZooKeeper
 session expires
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    [ https://issues.apache.org/jira/browse/HBASE-5549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13440351#comment-13440351 ] 

Himanshu Vashishtha commented on HBASE-5549:
--------------------------------------------

@Stack: So, currently (in this patch also), we don't wait for the Expired event, which is not correct.
In 6354, v2 patch also doesn't look for it.

I added this check (as mentioned earlier) but sometimes, the only event received is synConnected, and not the Expired event. So, it waits on the AtomicBoolean sessionClosed,  to become true, which will happen only when the watcher received the Expired event. Thinking today, it looks like we should invoke the close method only *after* the monitorwatcher is properly initialized. Hmmm, I will look at this today again.
                
> 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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