本篇内容主要讲解“zk中快速选举FastLeaderElection的实现方法”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“zk中快速选举FastLeaderElection的实现方法”吧!

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选举涉及概念

服务器状态

投票

如何选择投票？

协议

选举

如何进行选举？

epoch

发送者

接收者

发送队列

接收队列

服务器状态

public enum ServerState {

LOOKING,寻找Leader状态，当服务处于该状态时当前集群中没有Leader,因此需要进入Leader选举

FOLLOWING,跟随者状态，表示当前是Follower

LEADING,领导者状态，表明当前是Leader

OBSERVING ,观察者

}

Vote投票

id	被推荐的leader的sid
zxid	被推荐leader的事务id
electionEpoch	判断多个投票是否在同一轮选举周期中，在服务器是一个字增序列，进入新一轮投票后，都对该值进行加1
peerEpoch	被推荐的leader的epoch
state	当前服务器状态

内部类

有Messenger ToSend Notification类

Notifications让其他节点知道指定节点的投票发生了变化，可能是由于节点竞选或投票中有更高zxid或相同的zxid有更高的serverid

ToSend类用于包装发送的信息

Messenger分为

WorkerReceiver和WorkerSender

主要完成这两个对象信息的设置

LinkedBlockingQueue sendqueue;

LinkedBlockingQueue recvqueue;

public Vote lookForLeader() throws InterruptedException {
    try {
        self.jmxLeaderElectionBean = new LeaderElectionBean();
        MBeanRegistry.getInstance().register(self.jmxLeaderElectionBean, self.jmxLocalPeerBean);
    } catch (Exception e) {
        LOG.warn("Failed to register with JMX", e);
        self.jmxLeaderElectionBean = null;
    }

    self.start_fle = Time.currentElapsedTime();
    try {
        Map recvset = new HashMap();

        Map outofelection = new HashMap();

        int notTimeout = minNotificationInterval;

        synchronized (this) {
            logicalclock.incrementAndGet();
            updateProposal(getInitId(), getInitLastLoggedZxid(), getPeerEpoch());
        }

        LOG.info("New election. My id =  " + self.getId() + ", proposed zxid=0x" + Long.toHexString(proposedZxid));
        sendNotifications();

        SyncedLearnerTracker voteSet;

        /*
         * Loop in which we exchange notifications until we find a leader
         */

        while ((self.getPeerState() == ServerState.LOOKING) && (!stop)) {
            /*
             * Remove next notification from queue, times out after 2 times
             * the termination time
             */
            Notification n = recvqueue.poll(notTimeout, TimeUnit.MILLISECONDS);

            /*
             * Sends more notifications if haven't received enough.
             * Otherwise processes new notification.
             */
            if (n == null) {
                if (manager.haveDelivered()) {
                    sendNotifications();
                } else {
                    manager.connectAll();
                }

                /*
                 * Exponential backoff
                 */
                int tmpTimeOut = notTimeout * 2;
                notTimeout = (tmpTimeOut < maxNotificationInterval ? tmpTimeOut : maxNotificationInterval);
                LOG.info("Notification time out: " + notTimeout);
            } else if (validVoter(n.sid) && validVoter(n.leader)) {
                /*
                 * Only proceed if the vote comes from a replica in the current or next
                 * voting view for a replica in the current or next voting view.
                 */
                switch (n.state) {
                case LOOKING:
                    if (getInitLastLoggedZxid() == -1) {
                        LOG.debug("Ignoring notification as our zxid is -1");
                        break;
                    }
                    if (n.zxid == -1) {
                        LOG.debug("Ignoring notification from member with -1 zxid {}", n.sid);
                        break;
                    }
                    // If notification > current, replace and send messages out
                    if (n.electionEpoch > logicalclock.get()) {
                        logicalclock.set(n.electionEpoch);
                        recvset.clear();
                        if (totalOrderPredicate(n.leader, n.zxid, n.peerEpoch, getInitId(), getInitLastLoggedZxid(), getPeerEpoch())) {
                            updateProposal(n.leader, n.zxid, n.peerEpoch);
                        } else {
                            updateProposal(getInitId(), getInitLastLoggedZxid(), getPeerEpoch());
                        }
                        sendNotifications();
                    } else if (n.electionEpoch < logicalclock.get()) {
                        if (LOG.isDebugEnabled()) {
                            LOG.debug(
                                "Notification election epoch is smaller than logicalclock. n.electionEpoch = 0x" + Long.toHexString(n.electionEpoch)
                                + ", logicalclock=0x" + Long.toHexString(logicalclock.get()));
                        }
                        break;
                    } else if (totalOrderPredicate(n.leader, n.zxid, n.peerEpoch, proposedLeader, proposedZxid, proposedEpoch)) {
                        updateProposal(n.leader, n.zxid, n.peerEpoch);
                        sendNotifications();
                    }

                    if (LOG.isDebugEnabled()) {
                        LOG.debug("Adding vote: from=" + n.sid
                                  + ", proposed leader=" + n.leader
                                  + ", proposed zxid=0x" + Long.toHexString(n.zxid)
                                  + ", proposed election epoch=0x" + Long.toHexString(n.electionEpoch));
                    }

                    // don't care about the version if it's in LOOKING state
                    recvset.put(n.sid, new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch));

                    voteSet = getVoteTracker(recvset, new Vote(proposedLeader, proposedZxid, logicalclock.get(), proposedEpoch));

                    if (voteSet.hasAllQuorums()) {

                        // Verify if there is any change in the proposed leader
                        while ((n = recvqueue.poll(finalizeWait, TimeUnit.MILLISECONDS)) != null) {
                            if (totalOrderPredicate(n.leader, n.zxid, n.peerEpoch, proposedLeader, proposedZxid, proposedEpoch)) {
                                recvqueue.put(n);
                                break;
                            }
                        }

                        /*
                         * This predicate is true once we don't read any new
                         * relevant message from the reception queue
                         */
                        if (n == null) {
                            setPeerState(proposedLeader, voteSet);
                            Vote endVote = new Vote(proposedLeader, proposedZxid, logicalclock.get(), proposedEpoch);
                            leaveInstance(endVote);
                            return endVote;
                        }
                    }
                    break;
                case OBSERVING:
                    LOG.debug("Notification from observer: {}", n.sid);
                    break;
                case FOLLOWING:
                case LEADING:
                    /*
                     * Consider all notifications from the same epoch
                     * together.
                     */
                    if (n.electionEpoch == logicalclock.get()) {
                        recvset.put(n.sid, new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch));
                        voteSet = getVoteTracker(recvset, new Vote(n.version, n.leader, n.zxid, n.electionEpoch, n.peerEpoch, n.state));
                        if (voteSet.hasAllQuorums() && checkLeader(outofelection, n.leader, n.electionEpoch)) {
                            setPeerState(n.leader, voteSet);
                            Vote endVote = new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch);
                            leaveInstance(endVote);
                            return endVote;
                        }
                    }

                    /*
                     * Before joining an established ensemble, verify that
                     * a majority are following the same leader.
                     */
                    outofelection.put(n.sid, new Vote(n.version, n.leader, n.zxid, n.electionEpoch, n.peerEpoch, n.state));
                    voteSet = getVoteTracker(outofelection, new Vote(n.version, n.leader, n.zxid, n.electionEpoch, n.peerEpoch, n.state));

                    if (voteSet.hasAllQuorums() && checkLeader(outofelection, n.leader, n.electionEpoch)) {
                        synchronized (this) {
                            logicalclock.set(n.electionEpoch);
                            setPeerState(n.leader, voteSet);
                        }
                        Vote endVote = new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch);
                        leaveInstance(endVote);
                        return endVote;
                    }
                    break;
                default:
                    LOG.warn("Notification state unrecoginized: " + n.state + " (n.state), " + n.sid + " (n.sid)");
                    break;
                }
            } else {
                if (!validVoter(n.leader)) {
                    LOG.warn("Ignoring notification for non-cluster member sid {} from sid {}", n.leader, n.sid);
                }
                if (!validVoter(n.sid)) {
                    LOG.warn("Ignoring notification for sid {} from non-quorum member sid {}", n.leader, n.sid);
                }
            }
        }
        return null;
    } finally {
        try {
            if (self.jmxLeaderElectionBean != null) {
                MBeanRegistry.getInstance().unregister(self.jmxLeaderElectionBean);
            }
        } catch (Exception e) {
            LOG.warn("Failed to unregister with JMX", e);
        }
        self.jmxLeaderElectionBean = null;
        LOG.debug("Number of connection processing threads: {}", manager.getConnectionThreadCount());
    }
}


投票相关函数

更新投票字段

synchronized void updateProposal(long leader, long zxid, long epoch) {
    if (LOG.isDebugEnabled()) {
        LOG.debug("Updating proposal: " + leader
                  + " (newleader), 0x" + Long.toHexString(zxid)
                  + " (newzxid), " + proposedLeader
                  + " (oldleader), 0x" + Long.toHexString(proposedZxid)
                  + " (oldzxid)");
    }
    proposedLeader = leader;
    proposedZxid = zxid;
    proposedEpoch = epoch;
}

生成投票的函数
public synchronized Vote getVote() {
    return new Vote(proposedLeader, proposedZxid, proposedEpoch);
}


状态信息获取函数
private ServerState learningState() {
    if (self.getLearnerType() == LearnerType.PARTICIPANT) {
        LOG.debug("I am a participant: {}", self.getId());
        return ServerState.FOLLOWING;
    } else {
        LOG.debug("I am an observer: {}", self.getId());
        return ServerState.OBSERVING;
    }
}


获取参与投票服务器的标识id
private long getInitId() {
    if (self.getQuorumVerifier().getVotingMembers().containsKey(self.getId())) {
        return self.getId();
    } else {
        return Long.MIN_VALUE;
    }
}

获取最新的日志事务id
private long getInitLastLoggedZxid() {
    if (self.getLearnerType() == LearnerType.PARTICIPANT) {
        return self.getLastLoggedZxid();
    } else {
        return Long.MIN_VALUE;
    }
}



获取保存在文件中当前epoch
public long getCurrentEpoch() throws IOException {
    if (currentEpoch == -1) {
        currentEpoch = readLongFromFile(CURRENT_EPOCH_FILENAME);
    }
    return currentEpoch;
}



选举相关函数


判断当前 a pair (server id, zxid)是否赢得了当前选票，总而言之 ，当前选票和新选票，哪个id大就选哪一个

protected boolean totalOrderPredicate(long newId, long newZxid, long newEpoch, long curId, long curZxid, long curEpoch) {
    if (LOG.isDebugEnabled()) {
        LOG.debug("id: " + newId
                  + ", proposed id: " + curId
                  + ", zxid: 0x" + Long.toHexString(newZxid)
                  + ", proposed zxid: 0x" + Long.toHexString(curZxid));
    }

    if (self.getQuorumVerifier().getWeight(newId) == 0) {
        return false;
    }

    /*
     * We return true if one of the following three cases hold:
     * 1- New epoch is higher
     * 2- New epoch is the same as current epoch, but new zxid is higher
     * 3- New epoch is the same as current epoch, new zxid is the same
     *  as current zxid, but server id is higher.
     */

    return ((newEpoch > curEpoch)
            || ((newEpoch == curEpoch)
                && ((newZxid > curZxid)
                    || ((newZxid == curZxid)
                        && (newId > curId)))));
}


判断是否是Leader,把不是leader的情况拆出来
protected boolean checkLeader(Map votes, long leader, long electionEpoch) {

    boolean predicate = true;

    /*
     * If everyone else thinks I'm the leader, I must be the leader.
     * The other two checks are just for the case in which I'm not the
     * leader. If I'm not the leader and I haven't received a message
     * from leader stating that it is leading, then predicate is false.
     */

    if (leader != self.getId()) {
        if (votes.get(leader) == null) {
            predicate = false;
        } else if (votes.get(leader).getState() != ServerState.LEADING) {
            predicate = false;
        }
    } else if (logicalclock.get() != electionEpoch) {
        predicate = false;
    }

    return predicate;
}

开始新一轮竞选工作

public Vote lookForLeader() throws InterruptedException

选举中涉及的数据结构信息类

electionEpoch和peerEpoch区别

electionEpoch是选举周期，用于判断是不是他弄一个选举周期，从0开始累计

peerEpoch是当前周期

两个vote比较规则

依次比较peerEpoch,zxid,sid

peerEpoch代表所处周期，越大投票越新

peerEpoch相同时，zxid代表一个周期中事务记录，越大投票越新

peerEpoch,zxid均相同时，sid大的赢取选票

到此，相信大家对“zk中快速选举FastLeaderElection的实现方法”有了更深的了解，不妨来实际操作一番吧！这里是创新互联网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！

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