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Date: Fri, 29 Dec 2017 09:44:00 +0000 (UTC)
From: "Hadoop QA (JIRA)" <jira@apache.org>
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Message-ID: <JIRA.13126179.1513752398000.545915.1514540640098@Atlassian.JIRA>
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Subject: [jira] [Commented] (ZOOKEEPER-2959) ignore accepted epoch and
 LEADERINFO ack from observers when a newly elected leader computes new
 epoch
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archived-at: Fri, 29 Dec 2017 09:44:06 -0000


    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16306154#comment-16306154 ] 

Hadoop QA commented on ZOOKEEPER-2959:
--------------------------------------

-1 overall.  GitHub Pull Request  Build
      

    +1 @author.  The patch does not contain any @author tags.

    +0 tests included.  The patch appears to be a documentation patch that doesn't require tests.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    +1 findbugs.  The patch does not introduce any new Findbugs (version 3.0.1) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit warnings.

    -1 core tests.  The patch failed core unit tests.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/1391//testReport/
Findbugs warnings: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/1391//artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Console output: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/1391//console

This message is automatically generated.

> 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
>
> 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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