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https://issues.apache.org/jira/browse/ZOOKEEPER-2959?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alexander Shraer updated ZOOKEEPER-2959:
----------------------------------------
    Priority: Blocker  (was: Major)

> ignore accepted epoch and LEADERINFO ack from observers when a newly elected 
> leader computes new epoch
> ------------------------------------------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-2959
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2959
>             Project: ZooKeeper
>          Issue Type: Bug
>    Affects Versions: 3.4.10, 3.5.3
>            Reporter: xiangyq000
>            Priority: Blocker
>
> Once the ZooKeeper cluster finishes the election for new leader, all learners 
> report their accepted epoch to the leader for the computation of new cluster 
> epoch.
> org.apache.zookeeper.server.quorum.Leader#getEpochToPropose
> {code:java}
>     private final HashSet<Long> connectingFollowers = new HashSet<Long>();
>     public long getEpochToPropose(long sid, long lastAcceptedEpoch) throws 
> InterruptedException, IOException {
>         synchronized(connectingFollowers) {
>             if (!waitingForNewEpoch) {
>                 return epoch;
>             }
>             if (lastAcceptedEpoch >= epoch) {
>                 epoch = lastAcceptedEpoch+1;
>             }
>             connectingFollowers.add(sid);
>             QuorumVerifier verifier = self.getQuorumVerifier();
>             if (connectingFollowers.contains(self.getId()) &&
>                                             
> verifier.containsQuorum(connectingFollowers)) {
>                 waitingForNewEpoch = false;
>                 self.setAcceptedEpoch(epoch);
>                 connectingFollowers.notifyAll();
>             } else {
>                 long start = Time.currentElapsedTime();
>                 long cur = start;
>                 long end = start + self.getInitLimit()*self.getTickTime();
>                 while(waitingForNewEpoch && cur < end) {
>                     connectingFollowers.wait(end - cur);
>                     cur = Time.currentElapsedTime();
>                 }
>                 if (waitingForNewEpoch) {
>                     throw new InterruptedException("Timeout while waiting for 
> epoch from quorum");
>                 }
>             }
>             return epoch;
>         }
>     }
> {code}
> The computation will get an outcome once :
> # The leader has call method "getEpochToPropose"
> # The number of all reporters is greater than half of participants.
> The problem is, an observer server will also send its accepted epoch to the 
> leader, while this procedure treat observers as participants.
> Supposed that the cluster consists of 1 leader, 2 followers and 1 observer, 
> and now the leader and the observer have reported their accepted epochs while 
> neither of the followers has. Thus, the connectingFollowers set consists of 
> two elements, resulting in a size of 2, which is greater than half quorum, 
> namely, 2. Then QuorumVerifier#containsQuorum will return true, because it 
> does not check whether the elements of the parameter are participants.
> The same flaw exists in 
> org.apache.zookeeper.server.quorum.Leader#waitForEpochAck



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