zookeeper选举代码分析
Posted
tags:
篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了zookeeper选举代码分析相关的知识,希望对你有一定的参考价值。
本文将以zookeeper的3.4.6版本作为源码分析版本。主要的代码类包括QuorumPeerMain、QuorumPeer、FastLeaderElection、QuorumMaj等。
假设有a,b,c三个zookeeper服务,serverid分别是1、2、3:
1.先启动集群中的a服务,先投票自己a为leader,并将投票信息发送给自己;
QuorumPeerMain对象调用QuorumPeer线程的startLeaderElection方法,最终调用FastLeaderElection的lookForLeader方法
2.再启动集群中的b服务,先投票自己b为leader,并将投票信息发送给自己和a服务;
3.a收到b的投票信息,服务a通过对比算法,选择b为leader,并通知自己和服务b;
protected boolean totalOrderPredicate(long newId, long newZxid, long newEpoch, long curId, long curZxid, long curEpoch) { 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))))); }
4.服务a通过验证算法,确认b为leader;
5.服务b收到a的通知信息,通过验证算法b确认自身为leader;
protected boolean termPredicate( HashMap<Long, Vote> votes, Vote vote) { HashSet<Long> set = new HashSet<Long>(); /* * First make the views consistent. Sometimes peers will have * different zxids for a server depending on timing. */ for (Map.Entry<Long,Vote> entry : votes.entrySet()) { if (vote.equals(entry.getValue())){ set.add(entry.getKey()); } } return self.getQuorumVerifier().containsQuorum(set); } public boolean containsQuorum(HashSet<Long> set){ return (set.size() > half); }
6.服务c启动后,发现集群已经选出leader为服务b;
7.下面的代码是选举过程中最重要的代码:
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; } if (self.start_fle == 0) { self.start_fle = System.currentTimeMillis(); } try { HashMap<Long, Vote> recvset = new HashMap<Long, Vote>(); HashMap<Long, Vote> outofelection = new HashMap<Long, Vote>(); int notTimeout = finalizeWait; synchronized(this){ logicalclock++; updateProposal(getInitId(), getInitLastLoggedZxid(), getPeerEpoch()); } LOG.info("New election. My id = " + self.getId() + ", proposed zxid=0x" + Long.toHexString(proposedZxid)); sendNotifications(); /* * 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(self.getVotingView().containsKey(n.sid)) { /* * Only proceed if the vote comes from a replica in the * voting view. */ switch (n.state) { case LOOKING: System.out.println("receive message : electionEpoch,logicalclock"+n.electionEpoch+":"+logicalclock); // If notification > current, replace and send messages out if (n.electionEpoch > logicalclock) { logicalclock = 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) { if(LOG.isDebugEnabled()){ LOG.debug("Notification election epoch is smaller than logicalclock. n.electionEpoch = 0x" + Long.toHexString(n.electionEpoch) + ", logicalclock=0x" + Long.toHexString(logicalclock)); } 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)); } recvset.put(n.sid, new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch)); if (termPredicate(recvset, new Vote(proposedLeader, proposedZxid, logicalclock, proposedEpoch))) { // 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) { self.setPeerState((proposedLeader == self.getId()) ? ServerState.LEADING: learningState()); Vote endVote = new Vote(proposedLeader, proposedZxid, logicalclock, 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){ recvset.put(n.sid, new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch)); if(ooePredicate(recvset, outofelection, n)) { self.setPeerState((n.leader == self.getId()) ? ServerState.LEADING: learningState()); Vote endVote = new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch); leaveInstance(endVote); return endVote; } } /* * Before joining an established ensemble, verify * a majority is following the same leader. */ outofelection.put(n.sid, new Vote(n.version, n.leader, n.zxid, n.electionEpoch, n.peerEpoch, n.state)); if(ooePredicate(outofelection, outofelection, n)) { synchronized(this){ logicalclock = n.electionEpoch; self.setPeerState((n.leader == self.getId()) ? ServerState.LEADING: learningState()); } Vote endVote = new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch); leaveInstance(endVote); return endVote; } break; default: LOG.warn("Notification state unrecognized: {} (n.state), {} (n.sid)", n.state, n.sid); break; } } else { LOG.warn("Ignoring notification from non-cluster member " + 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; } }
以上是关于zookeeper选举代码分析的主要内容,如果未能解决你的问题,请参考以下文章
Zookeeper源码阅读(十八) 选举之快速选举算法FastLeaderElection