Vishal K commented on ZOOKEEPER-917:
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:
> * 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 126.96.36.199 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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