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https://issues.apache.org/jira/browse/ZOOKEEPER-2189?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hongchao Deng updated ZOOKEEPER-2189:
-------------------------------------
Description:
This was original JIRA of ZOOKEEPER-2203. For project management reason, all
the issues and related discussion are moved to ZOOKEEPER-2203. This JIRA is
linked to ZOOKEEPER-2098.
==============
This sequence leads the ensemble to a split-brain state:
* Start server 1 (config=1:participant, 2:participant, 3:participant)
* Start server 2 (config=1:participant, 2:participant, 3:participant)
* 1 and 2 believe 2 is the leader
* Start server 3 (config=1:observer, 2:observer, 3:participant)
* 3 believes 3 is the leader, although 1 and 2 still believe 2 is the leader
Such a split-brain ensemble is very unstable.
Znodes can be lost easily:
* Create some znodes on 2
* Restart 1 and 2
* 1, 2 and 3 can think 3 is the leader
* znodes created on 2 are lost, as 1 and 2 sync with 3
I consider this behavior as a bug and that ZK should fail gracefully if a
participant is listed as an observer in the config.
In current implementation, ZK cannot detect such an invalid config, as
FastLeaderElection.sendNotification() sends notifications to only voting
members and hence there is no message from observers(1 and 2) to the new voter
(3).
I think FastLeaderElection.sendNotification() should send notifications to all
the members and FastLeaderElection.Messenger.WorkerReceiver.run() should verify
acks.
Any thoughts?
was:
This was original JIRA of ZOOKEEPER-2203. For project management reason, all
the issues and related discussion are moved to ZOOKEEPER-2203. This JIRA is
linked to ZOOKEEPER-2098.
This sequence leads the ensemble to a split-brain state:
* Start server 1 (config=1:participant, 2:participant, 3:participant)
* Start server 2 (config=1:participant, 2:participant, 3:participant)
* 1 and 2 believe 2 is the leader
* Start server 3 (config=1:observer, 2:observer, 3:participant)
* 3 believes 3 is the leader, although 1 and 2 still believe 2 is the leader
Such a split-brain ensemble is very unstable.
Znodes can be lost easily:
* Create some znodes on 2
* Restart 1 and 2
* 1, 2 and 3 can think 3 is the leader
* znodes created on 2 are lost, as 1 and 2 sync with 3
I consider this behavior as a bug and that ZK should fail gracefully if a
participant is listed as an observer in the config.
In current implementation, ZK cannot detect such an invalid config, as
FastLeaderElection.sendNotification() sends notifications to only voting
members and hence there is no message from observers(1 and 2) to the new voter
(3).
I think FastLeaderElection.sendNotification() should send notifications to all
the members and FastLeaderElection.Messenger.WorkerReceiver.run() should verify
acks.
Any thoughts?
> QuorumCnxManager: use BufferedOutputStream for initial msg
> ----------------------------------------------------------
>
> Key: ZOOKEEPER-2189
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2189
> Project: ZooKeeper
> Issue Type: Bug
> Components: leaderElection
> Affects Versions: 3.5.0
> Reporter: Akihiro Suda
>
> This was original JIRA of ZOOKEEPER-2203. For project management reason, all
> the issues and related discussion are moved to ZOOKEEPER-2203. This JIRA is
> linked to ZOOKEEPER-2098.
> ==============
> This sequence leads the ensemble to a split-brain state:
> * Start server 1 (config=1:participant, 2:participant, 3:participant)
> * Start server 2 (config=1:participant, 2:participant, 3:participant)
> * 1 and 2 believe 2 is the leader
> * Start server 3 (config=1:observer, 2:observer, 3:participant)
> * 3 believes 3 is the leader, although 1 and 2 still believe 2 is the leader
> Such a split-brain ensemble is very unstable.
> Znodes can be lost easily:
> * Create some znodes on 2
> * Restart 1 and 2
> * 1, 2 and 3 can think 3 is the leader
> * znodes created on 2 are lost, as 1 and 2 sync with 3
> I consider this behavior as a bug and that ZK should fail gracefully if a
> participant is listed as an observer in the config.
> In current implementation, ZK cannot detect such an invalid config, as
> FastLeaderElection.sendNotification() sends notifications to only voting
> members and hence there is no message from observers(1 and 2) to the new
> voter (3).
> I think FastLeaderElection.sendNotification() should send notifications to
> all the members and FastLeaderElection.Messenger.WorkerReceiver.run() should
> verify acks.
> Any thoughts?
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