Hudson commented on ZOOKEEPER-159:

Integrated in ZooKeeper-trunk #108 (See 
    . Cover two corner cases of leader election

> Cover two corner cases of leader election
> -----------------------------------------
>                 Key: ZOOKEEPER-159
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-159
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: leaderElection
>            Reporter: Flavio Paiva Junqueira
>            Assignee: Flavio Paiva Junqueira
>             Fix For: 3.0.0
>         Attachments: ZOOKEEPER-159.patch
> In the default implementation of leader election, there are two undesirable 
> cases that need to be covered:
> 1- If there is a leader elected and this leader is supported by at least  
> quorum of peers, then it can happen that one peer disconnects from the 
> leader, and initiates a new leader election. As it is a new leader election, 
> we increment the logical clock of this peer, and according to the current 
> implementation, this peer won't accept any vote from a peer with a lower LE 
> turn (corresponds to the value of the logical clock of the voting peer). The 
> attached patch corrects this problem by allowing a peer to go back to a 
> previous epoch in the case a majority votes for a leader, and the peer also 
> receives a vote from the leader. This feature allows a peer to correct a 
> false suspicion of the current leader;
> 2- If a peer  advances to a new turn before others, then it may end up voting 
> for a peer that either does not have the highest server id or the the highest 
> zxid. The attached patch fixes this problem by resetting the vote a peer when 
> it updates its logical clock upon receiving a notification with a higher turn 
> value.

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