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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2959) ignore accepted epoch and LEADERINFO ack from observers when a newly elected leader computes new epoch
Date Thu, 19 Apr 2018 21:20:00 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16444818#comment-16444818
] 

ASF GitHub Bot commented on ZOOKEEPER-2959:
-------------------------------------------

Github user lavacat commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/500#discussion_r182887771
  
    --- Diff: src/java/test/org/apache/zookeeper/server/quorum/ZabUtils.java ---
    @@ -0,0 +1,140 @@
    +/**
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you under the Apache License, Version 2.0 (the
    + * "License"); you may not use this file except in compliance
    + * with the License.  You may obtain a copy of the License at
    + *
    + *     http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +
    +package org.apache.zookeeper.server.quorum;
    +
    +import org.apache.zookeeper.PortAssignment;
    +import org.apache.zookeeper.server.ServerCnxn;
    +import org.apache.zookeeper.server.ServerCnxnFactory;
    +import org.apache.zookeeper.server.ZKDatabase;
    +import org.apache.zookeeper.server.ZooKeeperServer;
    +import org.apache.zookeeper.server.persistence.FileTxnSnapLog;
    +import org.apache.zookeeper.server.quorum.flexible.QuorumMaj;
    +
    +import java.io.File;
    +import java.io.FileOutputStream;
    +import java.io.IOException;
    +import java.lang.reflect.Field;
    +import java.net.InetSocketAddress;
    +import java.util.HashMap;
    +
    +public class ZabUtils {
    +    public static final int SYNC_LIMIT = 2;
    +
    +    public static QuorumPeer createQuorumPeer(File tmpDir) throws IOException{
    +        QuorumPeer peer = new QuorumPeer();
    +        peer.syncLimit = 2;
    +        peer.initLimit = 2;
    +        peer.tickTime = 2000;
    +        peer.quorumPeers = new HashMap<Long, QuorumPeer.QuorumServer>();
    +        peer.quorumPeers.put(0L, new QuorumPeer.QuorumServer(0, "127.0.0.1", PortAssignment.unique(),
0, null));
    +        peer.quorumPeers.put(1L, new QuorumPeer.QuorumServer(1, "127.0.0.1", PortAssignment.unique(),
0, null));
    +        peer.quorumPeers.put(2L, new QuorumPeer.QuorumServer(2, "127.0.0.1", PortAssignment.unique(),
0, null));
    +        peer.setQuorumVerifier(new QuorumMaj(peer.quorumPeers.size()));
    +        peer.setCnxnFactory(new NullServerCnxnFactory());
    +        File version2 = new File(tmpDir, "version-2");
    +        version2.mkdir();
    +        FileOutputStream fos;
    +        fos = new FileOutputStream(new File(version2, "currentEpoch"));
    +        fos.write("0\n".getBytes());
    +        fos.close();
    +        fos = new FileOutputStream(new File(version2, "acceptedEpoch"));
    +        fos.write("0\n".getBytes());
    +        fos.close();
    +        return peer;
    +    }
    +
    +    public static Leader createLeader(File tmpDir, QuorumPeer peer)
    +            throws IOException, NoSuchFieldException, IllegalAccessException{
    +        LeaderZooKeeperServer zk = prepareLeader(tmpDir, peer);
    +        return new Leader(peer, zk);
    +    }
    +
    +    public static MockLeader createMockLeader(File tmpDir, QuorumPeer peer)
    +            throws IOException, NoSuchFieldException, IllegalAccessException{
    +        LeaderZooKeeperServer zk = prepareLeader(tmpDir, peer);
    +        return new MockLeader(peer, zk);
    +    }
    +
    +    private static LeaderZooKeeperServer prepareLeader(File tmpDir, QuorumPeer peer)
    +            throws IOException, NoSuchFieldException, IllegalAccessException {
    +        FileTxnSnapLog logFactory = new FileTxnSnapLog(tmpDir, tmpDir);
    +        peer.setTxnFactory(logFactory);
    +        Field addrField = peer.getClass().getDeclaredField("myQuorumAddr");
    +        addrField.setAccessible(true);
    +        addrField.set(peer, new InetSocketAddress(PortAssignment.unique()));
    +        ZKDatabase zkDb = new ZKDatabase(logFactory);
    +        return new LeaderZooKeeperServer(logFactory, peer, new ZooKeeperServer.BasicDataTreeBuilder(),
zkDb);
    +    }
    +
    +    private static final class NullServerCnxnFactory extends ServerCnxnFactory {
    +        public void startup(ZooKeeperServer zkServer) throws IOException,
    +                InterruptedException {
    +        }
    +        public void start() {
    +        }
    +        public void shutdown() {
    +        }
    +        public void setMaxClientCnxnsPerHost(int max) {
    +        }
    +        public void join() throws InterruptedException {
    +        }
    +        public int getMaxClientCnxnsPerHost() {
    +            return 0;
    +        }
    +        public int getLocalPort() {
    +            return 0;
    +        }
    +        public InetSocketAddress getLocalAddress() {
    +            return null;
    +        }
    +        public Iterable<ServerCnxn> getConnections() {
    +            return null;
    +        }
    +        public void configure(InetSocketAddress addr, int maxClientCnxns)
    +                throws IOException {
    +        }
    +        public void closeSession(long sessionId) {
    +        }
    +        public void closeAll() {
    +        }
    +        @Override
    +        public int getNumAliveConnections() {
    +            return 0;
    +        }
    +    }
    +
    +    static final class MockLeader extends Leader {
    --- End diff --
    
    Can't make it private, this class is still used in Zab1_0Test


> 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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