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https://issues.apache.org/jira/browse/ZOOKEEPER-2959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16445063#comment-16445063
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ASF GitHub Bot commented on ZOOKEEPER-2959:
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GitHub user lavacat opened a pull request:
https://github.com/apache/zookeeper/pull/503
ZOOKEEPER-2959: ignore accepted epoch and LEADERINFO ack from observers
https://issues.apache.org/jira/browse/ZOOKEEPER-2959
- added getVotingMembers check for id in getEpochToPropose and
waitForEpochAck
- removed unused learnerType param in waitForNewLeaderAck
- unit tests
- refactored common test helpers into ZabUtils
credit: Xiang Yongqiang (https://github.com/xyq000) for original PR and
reporting the issue
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/lavacat/zookeeper branch-3.5
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/zookeeper/pull/503.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #503
----
commit d7181d65f66adcfc0fecda2670580e2d2b8ddccb
Author: Bogdan Kanivets <bkanivets@...>
Date: 2018-04-20T00:02:59Z
ZOOKEEPER-2959: ignore accepted epoch and LEADERINFO ack from observers
https://issues.apache.org/jira/browse/ZOOKEEPER-2959
- added getVotingMembers check for id in getEpochToPropose and
waitForEpochAck
- removed unused learnerType param in waitForNewLeaderAck
- unit tests
- refactored common test helpers into ZabUtils
credit: Xiang Yongqiang (https://github.com/xyq000) for original PR and
reporting the issue
----
> 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
> Assignee: Bogdan Kanivets
> 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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