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https://issues.apache.org/jira/browse/S4-3?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13127685#comment-13127685
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kishore gopalakrishna commented on S4-3:
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Flavio, the session close will work but compared to checking pNode exists it is
more difficult. Also closing session may not be a good idea if we add more
ephemeral in other parts of the code. So the right thing to do would be to
check for pNode exists and ephemeralOwner comparison.
Gavin, do you know how the process will restart in Hbase,Hedwig ? I think they
might have some daemon process running that will restart a process if its down
but we dont have such scripts. Also its not guaranteed that this will happen
only during start up, this might happen any time a pNode is created which is
either at start up or when another node dies and a standby pick up the task.
As Flavio mentioned read after write is guaranteed and we should be fine with
checking for pNode existence.
> 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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