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From "Gavin Li (Issue Comment Edited) (JIRA)" <j...@apache.org>
Subject [jira] [Issue Comment Edited] (S4-3) Sometimes one process node owns 2 tasks
Date Tue, 11 Oct 2011 03:22:29 GMT

    [ https://issues.apache.org/jira/browse/S4-3?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13124657#comment-13124657
] 

Gavin Li edited comment on S4-3 at 10/11/11 3:21 AM:
-----------------------------------------------------

attach a patch fixing the handling of loss connection exception when creating ephemeral znode
                
      was (Author: gavin_li):
    fix the handling of loss connection exception when creating ephemeral 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
>         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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