Vishal K commented on ZOOKEEPER-917:

Hi Flavio,

Lets see if I understand this right. Server 2 was replaced and became the 
leader. Server 2 receives old notifications from others and accepts leadership 
even if its <epoch, zxid> prior to receiving any notifications was <1,0>.

Server 2 accepts leadership because 0, 1 vote for 2 and we allow 2 to become 
leader based on point 1. in your comment on 07/Nov/10.

My question with regards to point 1.:
- In your example, it is OK to allow A to join the cluster and become a 
follower (so that A does not remain locked out). But is it OK for A to accept 
leadership even if it has not seen the zxid reported by others (regardless of 
the votes)? Shouldn't it reject leadership?

Am I still misunderstanding the problem?

> 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:
>   *
>   *
>   *
> failed, and was replaced by a new node 
> (automated startup). The new node had not participated in any zookeeper 
> quorum previously. The node 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 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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