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https://issues.apache.org/jira/browse/S4-3?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13126913#comment-13126913
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kishore gopalakrishna commented on S4-3:
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Agree with Flavio, instead of exiting we should think of solution;
Closing the session might be difficult to implement, checking if pNode exists
after exception seems to be sufficient. How ever just this check may not be
sufficient, additional check is necessary to see if the EphemeralOwner of the
Node is same as the sessionId. Otherwise, some other node might have acquired
that task and this node thinks it acquired it.
So along with pNode exists check if it was created by created by same process
either by checking ephemeralOwner or reading contents of the znode.
> Sometimes one process node owns 2 tasks
> ---------------------------------------
>
> Key: S4-3
> URL: https://issues.apache.org/jira/browse/S4-3
> Project: Apache S4
> Issue Type: Bug
> Reporter: Gavin Li
> Assignee: Gavin Li
> Attachments: s4_loscon_fix
>
>
> When using S4, we found sometimes it ends up with one process node owns 2
> tasks. I did some investigation, it seems that the handling of
> ConnectionLossException when creating the ephemeral node is problematic.
> Sometimes when the response from zookeeper server times out,
> zookeeper.create() will fail with ConnectionLossException while the creation
> request might already be sent to server(see
> http://svn.apache.org/viewvc/hadoop/zookeeper/trunk/src/java/main/org/apache/zookeeper/ClientCnxn.java
> line 830). From our logs this is the case we ran into.
> Maybe we should handle it in the way that HBase is handling it
> (http://svn.apache.org/viewvc/hbase/trunk/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKUtil.java?view=markup),
> just simply exit the process when got that exception to let the whole
> process restart.
> To be more clear, what happened was: a process node called zookeeper.create()
> to acquire a task, the request was successfully sent to zookeeper server, but
> the zookeeper IO loop timed out before the response came. So the
> zookeeper.create() failed with ConnectionLossException. Then the process node
> ignored this exception and tried to acquire another task. Then it got 2 tasks.
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