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https://issues.apache.org/jira/browse/ZOOKEEPER-1514?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13423776#comment-13423776
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Flavio Junqueira commented on ZOOKEEPER-1514:
---------------------------------------------
I used blame to track where we have introduced the check in tests for the first
time. I believe it started with ZOOKEEPER-480, and we were essentially trying
to implement a mock server. If you check QuorumPeer.createElectionAlgorithm(),
this is essentially what we are doing there. I'd rather leave as is, and if you
feel we need to revisit the way we are starting the listener, then perhaps we
need to create another jira for it, since it touches other parts of the code
base.
I'll upload a patch with the other modifications you suggested, so that if you
agree with my assessment, then we can move forward with that one.
> FastLeaderElection - leader ignores the round information when joining a
> quorum
> -------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-1514
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1514
> Project: ZooKeeper
> Issue Type: Bug
> Components: quorum
> Affects Versions: 3.3.4
> Reporter: Patrick Hunt
> Assignee: Flavio Junqueira
> Priority: Critical
> Fix For: 3.4.4, 3.5.0, 3.3.7
>
> Attachments: ZOOKEEPER-1514.patch, ZOOKEEPER-1514.patch
>
>
> In the following case we have a 3 server ensemble.
> Initially all is well, zk3 is the leader.
> However zk3 fails, restarts, and rejoins the quorum as the new leader (was
> the old leader, still the leader after re-election)
> The existing two followers, zk1 and zk2 rejoin the new quorum again as
> followers of zk3.
> zk1 then fails, the datadirectory is deleted (so it has no state whatsoever)
> and restarted. However zk1 can never rejoin the quorum (even after an hour).
> During this time zk2 and zk3 are serving properly.
> Later all three servers are later restarted and properly form a functional
> quourm.
> Here are some interesting log snippets. Nothing else of interest was seen in
> the logs during this time:
> zk3. This is where it becomes the leader after failing initially (as the
> leader). Notice the "round" is ahead of zk1 and zk2:
> {noformat}
> 2012-07-18 17:19:35,423 - INFO
> [QuorumPeer:/0.0.0.0:2181:FastLeaderElection@663] - New election. My id = 3,
> Proposed zxid = 77309411648
> 2012-07-18 17:19:35,423 - INFO [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 3 (n.leader), 77309411648
> (n.zxid), 832 (n.round), LOOKING (n.state), 3 (n.sid), LOOKING (my state)
> 2012-07-18 17:19:35,424 - INFO [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 3 (n.leader), 73014444480
> (n.zxid), 831 (n.round), FOLLOWING (n.state), 2 (n.sid), LOOKING (my state)
> 2012-07-18 17:19:35,424 - INFO [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 3 (n.leader), 73014444480
> (n.zxid), 831 (n.round), FOLLOWING (n.state), 1 (n.sid), LOOKING (my state)
> 2012-07-18 17:19:35,424 - INFO [QuorumPeer:/0.0.0.0:2181:QuorumPeer@655] -
> LEADING
> {noformat}
> zk1 which won't come back. Notice that zk3 is reporting the round as 831,
> while zk2 thinks that the round is 832:
> {noformat}
> 2012-07-18 17:31:12,015 - INFO [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 1 (n.leader), 77309411648
> (n.zxid), 1 (n.round), LOOKING (n.state), 1 (n.sid), LOOKING (my state)
> 2012-07-18 17:31:12,016 - INFO [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 3 (n.leader), 73014444480
> (n.zxid), 831 (n.round), LEADING (n.state), 3 (n.sid), LOOKING (my state)
> 2012-07-18 17:31:12,017 - INFO [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 3 (n.leader), 77309411648
> (n.zxid), 832 (n.round), FOLLOWING (n.state), 2 (n.sid), LOOKING (my state)
> 2012-07-18 17:31:15,219 - INFO
> [QuorumPeer:/0.0.0.0:2181:FastLeaderElection@697] - Notification time out:
> 6400
> {noformat}
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