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From "Vishal K (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-917) Leader election selected incorrect leader
Date Mon, 08 Nov 2010 15:57:08 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-917?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12929602#action_12929602
] 

Vishal K commented on ZOOKEEPER-917:
------------------------------------

Hi Flavio,

Thanks for the clarification.

Looks like this scenario is not likely to happen if replace is done carefully. For the sake
of argument, shouldn't we make the exception that you described only if the joining peer is
going to be a follower? For the problem reported in this jira,  the server that was replaced
(server 2) will not have seen the zxid received in the notifications from the other two nodes.
Therefore, is this case, will it make sense for server 2 to start a new round of election?

-Vishal



> Leader election selected incorrect leader
> -----------------------------------------
>
>                 Key: ZOOKEEPER-917
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-917
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: leaderElection, server
>    Affects Versions: 3.2.2
>         Environment: Cloudera distribution of zookeeper (patched to never cache DNS entries)
> Debian lenny
>            Reporter: Alexandre Hardy
>            Priority: Critical
>             Fix For: 3.3.3, 3.4.0
>
>         Attachments: zklogs-20101102144159SAST.tar.gz
>
>
> We had three nodes running zookeeper:
>   * 192.168.130.10
>   * 192.168.130.11
>   * 192.168.130.14
> 192.168.130.11 failed, and was replaced by a new node 192.168.130.13 (automated startup).
The new node had not participated in any zookeeper quorum previously. The node 192.148.130.11
was permanently removed from service and could not contribute to the quorum any further (powered
off).
> DNS entries were updated for the new node to allow all the zookeeper servers to find
the new node.
> The new node 192.168.130.13 was selected as the LEADER, despite the fact that it had
not seen the latest zxid.
> This particular problem has not been verified with later versions of zookeeper, and no
attempt has been made to reproduce this problem as yet.

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