05、ZooKeeper 角色初始化
zookeeper有如下三个角色：
1、 Leader；
2、 Follower；
3、 Observer；
在QuorumPeer的run方法中会根据当前节点的状态执行不同的操作
// QuorumPeer
public void run() {
// 省略
try {
/*
* Main loop
*/
while (running) {
switch (getPeerState()) {
case LOOKING:
LOG.info("LOOKING");
if (Boolean.getBoolean("readonlymode.enabled")) {
LOG.info("Attempting to start ReadOnlyZooKeeperServer");
// Create read-only server but don't start it immediately
final ReadOnlyZooKeeperServer roZk =
new ReadOnlyZooKeeperServer(logFactory, this, this.zkDb);
// Instead of starting roZk immediately, wait some grace
// period before we decide we're partitioned.
//
// Thread is used here because otherwise it would require
// changes in each of election strategy classes which is
// unnecessary code coupling.
Thread roZkMgr = new Thread() {
public void run() {
try {
// lower-bound grace period to 2 secs
sleep(Math.max(2000, tickTime));
if (ServerState.LOOKING.equals(getPeerState())) {
roZk.startup();
}
} catch (InterruptedException e) {
LOG.info("Interrupted while attempting to start ReadOnlyZooKeeperServer, not started");
} catch (Exception e) {
LOG.error("FAILED to start ReadOnlyZooKeeperServer", e);
}
}
};
try {
roZkMgr.start();
reconfigFlagClear();
if (shuttingDownLE) {
shuttingDownLE = false;
startLeaderElection();
}
setCurrentVote(makeLEStrategy().lookForLeader());
} catch (Exception e) {
LOG.warn("Unexpected exception", e);
setPeerState(ServerState.LOOKING);
} finally {
// If the thread is in the the grace period, interrupt
// to come out of waiting.
roZkMgr.interrupt();
roZk.shutdown();
}
} else {
try {
reconfigFlagClear();
if (shuttingDownLE) {
shuttingDownLE = false;
startLeaderElection();
}
setCurrentVote(makeLEStrategy().lookForLeader());
} catch (Exception e) {
LOG.warn("Unexpected exception", e);
setPeerState(ServerState.LOOKING);
}
}
break;
case OBSERVING:
try {
LOG.info("OBSERVING");
setObserver(makeObserver(logFactory));
observer.observeLeader();
} catch (Exception e) {
LOG.warn("Unexpected exception",e );
} finally {
observer.shutdown();
setObserver(null);
updateServerState();
}
break;
case FOLLOWING:
try {
LOG.info("FOLLOWING");
setFollower(makeFollower(logFactory));
follower.followLeader();
} catch (Exception e) {
LOG.warn("Unexpected exception",e);
} finally {
follower.shutdown();
setFollower(null);
updateServerState();
}
break;
case LEADING:
LOG.info("LEADING");
try {
setLeader(makeLeader(logFactory));
leader.lead();
setLeader(null);
} catch (Exception e) {
LOG.warn("Unexpected exception",e);
} finally {
if (leader != null) {
leader.shutdown("Forcing shutdown");
setLeader(null);
}
updateServerState();
}
break;
}
start_fle = Time.currentElapsedTime();
}
} finally {
// 省略
}
}
下面分别看下不同角色都做了哪些操作
Leader
case LEADING:
LOG.info("LEADING");
try {
// 1. 创建Leader对象并赋值到leader属性上
setLeader(makeLeader(logFactory));
// 2. 运行leader
leader.lead();
setLeader(null);
} catch (Exception e) {
LOG.warn("Unexpected exception",e);
} finally {
// 出现异常
// 3. 关闭leader
if (leader != null) {
leader.shutdown("Forcing shutdown");
setLeader(null);
}
// 4. 更新服务器状态为looking，重新开始选举
updateServerState();
}
break;
}
创建
protected Leader makeLeader(FileTxnSnapLog logFactory) throws IOException, X509Exception {
return new Leader(this, new LeaderZooKeeperServer(logFactory, this, this.zkDb));
}
// Leader
Leader(QuorumPeer self,LeaderZooKeeperServer zk) throws IOException {
this.self = self;
this.proposalStats = new BufferStats();
// 监听本地用来和其他节点交换数据的端口，等待其他节点连接
// localhost:28888:3888 中用来和其他节点进行交换的端口就是28888
try {
if (self.shouldUsePortUnification() || self.isSslQuorum()) {
boolean allowInsecureConnection = self.shouldUsePortUnification();
if (self.getQuorumListenOnAllIPs()) {
ss = new UnifiedServerSocket(self.getX509Util(), allowInsecureConnection, self.getQuorumAddress().getPort());
} else {
ss = new UnifiedServerSocket(self.getX509Util(), allowInsecureConnection);
}
} else {
if (self.getQuorumListenOnAllIPs()) {
ss = new ServerSocket(self.getQuorumAddress().getPort());
} else {
ss = new ServerSocket();
}
}
ss.setReuseAddress(true);
if (!self.getQuorumListenOnAllIPs()) {
ss.bind(self.getQuorumAddress());
}
} catch (BindException e) {
if (self.getQuorumListenOnAllIPs()) {
LOG.error("Couldn't bind to port " + self.getQuorumAddress().getPort(), e);
} else {
LOG.error("Couldn't bind to " + self.getQuorumAddress(), e);
}
throw e;
}
this.zk = zk;
this.learnerSnapshotThrottler = createLearnerSnapshotThrottler(
maxConcurrentSnapshots, maxConcurrentSnapshotTimeout);
}
运行
首先整体看下leader的运行逻辑
void lead() throws IOException, InterruptedException {
// 1. 计算选举耗时并打印
self.end_fle = Time.currentElapsedTime();
long electionTimeTaken = self.end_fle - self.start_fle;
self.setElectionTimeTaken(electionTimeTaken);
LOG.info("LEADING - LEADER ELECTION TOOK - {} {}", electionTimeTaken,
QuorumPeer.FLE_TIME_UNIT);
self.start_fle = 0;
self.end_fle = 0;
zk.registerJMX(new LeaderBean(this, zk), self.jmxLocalPeerBean);
try {
self.tick.set(0);
// 2. 加载数据
zk.loadData();
leaderStateSummary = new StateSummary(self.getCurrentEpoch(), zk.getLastProcessedZxid());
// Start thread that waits for connection requests from
// new followers.
// 3. 开启接收线程，等待其他follower连接
cnxAcceptor = new LearnerCnxAcceptor();
cnxAcceptor.start();
// 4. 等待过半follower连接，生成新的epoch
long epoch = getEpochToPropose(self.getId(), self.getAcceptedEpoch());
// 5. 设置当前zxid
zk.setZxid(ZxidUtils.makeZxid(epoch, 0));
synchronized(this){
lastProposed = zk.getZxid();
}
newLeaderProposal.packet = new QuorumPacket(NEWLEADER, zk.getZxid(),
null, null);
if ((newLeaderProposal.packet.getZxid() & 0xffffffffL) != 0) {
LOG.info("NEWLEADER proposal has Zxid of "
+ Long.toHexString(newLeaderProposal.packet.getZxid()));
}
QuorumVerifier lastSeenQV = self.getLastSeenQuorumVerifier();
QuorumVerifier curQV = self.getQuorumVerifier();
if (curQV.getVersion() == 0 && curQV.getVersion() == lastSeenQV.getVersion()) {
// This was added in ZOOKEEPER-1783. The initial config has version 0 (not explicitly
// specified by the user; the lack of version in a config file is interpreted as version=0).
// As soon as a config is established we would like to increase its version so that it
// takes presedence over other initial configs that were not established (such as a config
// of a server trying to join the ensemble, which may be a partial view of the system, not the full config).
// We chose to set the new version to the one of the NEWLEADER message. However, before we can do that
// there must be agreement on the new version, so we can only change the version when sending/receiving UPTODATE,
// not when sending/receiving NEWLEADER. In other words, we can't change curQV here since its the committed quorum verifier,
// and there's still no agreement on the new version that we'd like to use. Instead, we use
// lastSeenQuorumVerifier which is being sent with NEWLEADER message
// so its a good way to let followers know about the new version. (The original reason for sending
// lastSeenQuorumVerifier with NEWLEADER is so that the leader completes any potentially uncommitted reconfigs
// that it finds before starting to propose operations. Here we're reusing the same code path for
// reaching consensus on the new version number.)
// It is important that this is done before the leader executes waitForEpochAck,
// so before LearnerHandlers return from their waitForEpochAck
// hence before they construct the NEWLEADER message containing
// the last-seen-quorumverifier of the leader, which we change below
try {
QuorumVerifier newQV = self.configFromString(curQV.toString());
newQV.setVersion(zk.getZxid());
self.setLastSeenQuorumVerifier(newQV, true);
} catch (Exception e) {
throw new IOException(e);
}
}
newLeaderProposal.addQuorumVerifier(self.getQuorumVerifier());
if (self.getLastSeenQuorumVerifier().getVersion() > self.getQuorumVerifier().getVersion()){
newLeaderProposal.addQuorumVerifier(self.getLastSeenQuorumVerifier());
}
// We have to get at least a majority of servers in sync with
// us. We do this by waiting for the NEWLEADER packet to get
// acknowledged
// 6. 等待过半的投票参与者响应了LEADERINFO信息，然后设置epoch
waitForEpochAck(self.getId(), leaderStateSummary);
self.setCurrentEpoch(epoch);
try {
// 7. 等待过半的投票参与者响应了NEWLEADER
waitForNewLeaderAck(self.getId(), zk.getZxid());
} catch (InterruptedException e) {
shutdown("Waiting for a quorum of followers, only synced with sids: [ "
+ newLeaderProposal.ackSetsToString() + " ]");
HashSet<Long> followerSet = new HashSet<Long>();
for(LearnerHandler f : getLearners()) {
if (self.getQuorumVerifier().getVotingMembers().containsKey(f.getSid())){
followerSet.add(f.getSid());
}
}
boolean initTicksShouldBeIncreased = true;
for (Proposal.QuorumVerifierAcksetPair qvAckset:newLeaderProposal.qvAcksetPairs) {
if (!qvAckset.getQuorumVerifier().containsQuorum(followerSet)) {
initTicksShouldBeIncreased = false;
break;
}
}
if (initTicksShouldBeIncreased) {
LOG.warn("Enough followers present. "+
"Perhaps the initTicks need to be increased.");
}
return;
}
// 8. 启动zk服务器
startZkServer();
/**
* WARNING: do not use this for anything other than QA testing
* on a real cluster. Specifically to enable verification that quorum
* can handle the lower 32bit roll-over issue identified in
* ZOOKEEPER-1277. Without this option it would take a very long
* time (on order of a month say) to see the 4 billion writes
* necessary to cause the roll-over to occur.
*
* This field allows you to override the zxid of the server. Typically
* you'll want to set it to something like 0xfffffff0 and then
* start the quorum, run some operations and see the re-election.
*/
String initialZxid = System.getProperty("zookeeper.testingonly.initialZxid");
if (initialZxid != null) {
long zxid = Long.parseLong(initialZxid);
zk.setZxid((zk.getZxid() & 0xffffffff00000000L) | zxid);
}
if (!System.getProperty("zookeeper.leaderServes", "yes").equals("no")) {
self.setZooKeeperServer(zk);
}
self.adminServer.setZooKeeperServer(zk);
// Everything is a go, simply start counting the ticks
// WARNING: I couldn't find any wait statement on a synchronized
// block that would be notified by this notifyAll() call, so
// I commented it out
//synchronized (this) {
// notifyAll();
//}
// We ping twice a tick, so we only update the tick every other
// iteration
boolean tickSkip = true;
// If not null then shutdown this leader
String shutdownMessage = null;
// 9. 向其他节点发送心跳
// 1个tickTime中会发送两次ping
// 每两次会判断是否有过半的节点仍然和leader保持心跳，如果没有过半，会关闭当前leader
while (true) {
synchronized (this) {
long start = Time.currentElapsedTime();
long cur = start;
long end = start + self.tickTime / 2;
while (cur < end) {
wait(end - cur);
cur = Time.currentElapsedTime();
}
if (!tickSkip) {
self.tick.incrementAndGet();
}
// We use an instance of SyncedLearnerTracker to
// track synced learners to make sure we still have a
// quorum of current (and potentially next pending) view.
SyncedLearnerTracker syncedAckSet = new SyncedLearnerTracker();
syncedAckSet.addQuorumVerifier(self.getQuorumVerifier());
if (self.getLastSeenQuorumVerifier() != null
&& self.getLastSeenQuorumVerifier().getVersion() > self
.getQuorumVerifier().getVersion()) {
syncedAckSet.addQuorumVerifier(self
.getLastSeenQuorumVerifier());
}
syncedAckSet.addAck(self.getId());
for (LearnerHandler f : getLearners()) {
if (f.synced()) {
syncedAckSet.addAck(f.getSid());
}
}
// check leader running status
if (!this.isRunning()) {
// set shutdown flag
shutdownMessage = "Unexpected internal error";
break;
}
if (!tickSkip && !syncedAckSet.hasAllQuorums()) {
// Lost quorum of last committed and/or last proposed
// config, set shutdown flag
shutdownMessage = "Not sufficient followers synced, only synced with sids: [ "
+ syncedAckSet.ackSetsToString() + " ]";
break;
}
tickSkip = !tickSkip;
}
for (LearnerHandler f : getLearners()) {
f.ping();
}
}
if (shutdownMessage != null) {
shutdown(shutdownMessage);
// leader goes in looking state
}
} finally {
zk.unregisterJMX(this);
}
}
下面看下创建的LearnerCnxAcceptor做了什么
// LearnerCnxAcceptor
@Override
public void run() {
try {
while (!stop) {
Socket s = null;
boolean error = false;
try {
// 1. 接收连接
s = ss.accept();
// start with the initLimit, once the ack is processed
// in LearnerHandler switch to the syncLimit
// 2. 设置连接
// 设置read操作阻塞的超时时间，如果在指定的时间内一直没有数据可以读取，会抛出异常
s.setSoTimeout(self.tickTime * self.initLimit);
s.setTcpNoDelay(nodelay);
BufferedInputStream is = new BufferedInputStream(
s.getInputStream());
// 3. 创建LearnerHandler并启动
LearnerHandler fh = new LearnerHandler(s, is, Leader.this);
fh.start();
} catch (SocketException e) {
error = true;
if (stop) {
LOG.info("exception while shutting down acceptor: "
+ e);
// When Leader.shutdown() calls ss.close(),
// the call to accept throws an exception.
// We catch and set stop to true.
stop = true;
} else {
throw e;
}
} catch (SaslException e){
LOG.error("Exception while connecting to quorum learner", e);
error = true;
} catch (Exception e) {
error = true;
throw e;
} finally {
// Don't leak sockets on errors
if (error && s != null && !s.isClosed()) {
try {
s.close();
} catch (IOException e) {
LOG.warn("Error closing socket", e);
}
}
}
}
} catch (Exception e) {
LOG.warn("Exception while accepting follower", e.getMessage());
handleException(this.getName(), e);
}
}
可以看到LearnerCnxAcceptor做的主要就是监听端口，每接收一个连接请求，就创建一个LearnerHandler来处理这个新建立的连接
下面综合Leader和LearnerHandle来看leader和其他节点之间的通信同步过程
获取对端节点信息
从对端节点的输入流中读取数据，然后解析数据，得到对端节点的id,version,configVersion,lastAcceptedEpoch等信息
// LearnerHandler
public void run() {
leader.addLearnerHandler(this);
tickOfNextAckDeadline = leader.self.tick.get()
+ leader.self.initLimit + leader.self.syncLimit;
ia = BinaryInputArchive.getArchive(bufferedInput);
bufferedOutput = new BufferedOutputStream(sock.getOutputStream());
oa = BinaryOutputArchive.getArchive(bufferedOutput);
QuorumPacket qp = new QuorumPacket();
// 从对端读取数据
ia.readRecord(qp, "packet");
if(qp.getType() != Leader.FOLLOWERINFO && qp.getType() != Leader.OBSERVERINFO){
LOG.error("First packet " + qp.toString()
+ " is not FOLLOWERINFO or OBSERVERINFO!");
return;
}
// 解析对端节点的信息
byte learnerInfoData[] = qp.getData();
if (learnerInfoData != null) {
ByteBuffer bbsid = ByteBuffer.wrap(learnerInfoData);
// sid
if (learnerInfoData.length >= 8) {
this.sid = bbsid.getLong();
}
// version
if (learnerInfoData.length >= 12) {
this.version = bbsid.getInt(); // protocolVersion
}
// configVersion
if (learnerInfoData.length >= 20) {
long configVersion = bbsid.getLong();
if (configVersion > leader.self.getQuorumVerifier().getVersion()) {
throw new IOException("Follower is ahead of the leader (has a later activated configuration)");
}
}
} else {
this.sid = leader.followerCounter.getAndDecrement();
}
if (leader.self.getView().containsKey(this.sid)) {
LOG.info("Follower sid: " + this.sid + " : info : "
+ leader.self.getView().get(this.sid).toString());
} else {
LOG.info("Follower sid: " + this.sid + " not in the current config " + Long.toHexString(leader.self.getQuorumVerifier().getVersion()));
}
// 节点角色
if (qp.getType() == Leader.OBSERVERINFO) {
learnerType = LearnerType.OBSERVER;
}
// 最新的epoch
long lastAcceptedEpoch = ZxidUtils.getEpochFromZxid(qp.getZxid());
// 省略
}
生成当前epoch
// Leader
void lead() {
long epoch = getEpochToPropose(self.getId(), self.getAcceptedEpoch());
}
// LearnerHandler
public void run() {
long newEpoch = leader.getEpochToPropose(this.getSid(), lastAcceptedEpoch);
long newLeaderZxid = ZxidUtils.makeZxid(newEpoch, 0);
}
getEpochToPropose主要作用是等待过半learner和当前的leader建立了连接，通过每个learner发给leader消息中的epoch，来计算最新的epoch
// 已经和当前leader建立连接的follower集合
protected final Set<Long> connectingFollowers = new HashSet<Long>();
// Leader
public long getEpochToPropose(long sid, long lastAcceptedEpoch) throws InterruptedException, IOException {
// 并发操作connectingFollowers
synchronized(connectingFollowers) {
// 如果已经计算过新的epoch，直接返回
if (!waitingForNewEpoch) {
return epoch;
}
// 接收到的epoch大于当前的epoch，更新
if (lastAcceptedEpoch >= epoch) {
epoch = lastAcceptedEpoch+1;
}
// 当前节点是选举参与者
// 将该节点加入到并发操作connectingFollowers集合中，代表leader已经和其建立了连接
if (isParticipant(sid)) {
connectingFollowers.add(sid);
}
QuorumVerifier verifier = self.getQuorumVerifier();
// 判断leader是否已经和过半的参与者建立了连接
if (connectingFollowers.contains(self.getId()) &&
verifier.containsQuorum(connectingFollowers)) {
// 修改标志，新的epoch已经计算完毕
waitingForNewEpoch = false;
// 设置epoch
self.setAcceptedEpoch(epoch);
// 唤醒所有阻塞线程
connectingFollowers.notifyAll();
} else {
long start = Time.currentElapsedTime();
long cur = start;
long end = start + self.getInitLimit()*self.getTickTime();
// 阻塞等待过半follower连接
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;
}
}
从上面的代码中可以看出该方法的过程如下：
1、 判断和leader建立连接的对端节点是否是参与者，如果是参与者，将其加入到connectingFollowers中；
2、 使用对端节点的epoch来计算leader的最新epoch，保证leader的最新epoch为所有接收到的epoch中的最大值+1；
3、 如果过半的参与者已经和leader建立了连接，那么此时epoch更新完毕，唤醒所有阻塞在计算最新epoch的线程，继续往下执行；
4、 如果没有过半的参与者和leader建立连接，那么会阻塞，并且等待过半的参与者和leader建立连接；
确认生成的epoch
// Leader
void lead() {
// 等待过半参与者对生成的epoch ack
waitForEpochAck(self.getId(), leaderStateSummary);
// 设置当前的epoch
self.setCurrentEpoch(epoch);
}
// LearnerHandler
public void run() {
byte ver[] = new byte[4];
ByteBuffer.wrap(ver).putInt(0x10000);
// 向对端节点发送LEADERINFO，该信息带有生成的epoch
QuorumPacket newEpochPacket = new QuorumPacket(Leader.LEADERINFO, newLeaderZxid, ver, null);
oa.writeRecord(newEpochPacket, "packet");
bufferedOutput.flush();
// 读取对端节点输入流，获取对端节点对生成的epoch的响应
QuorumPacket ackEpochPacket = new QuorumPacket();
ia.readRecord(ackEpochPacket, "packet");
if (ackEpochPacket.getType() != Leader.ACKEPOCH) {
LOG.error(ackEpochPacket.toString()
+ " is not ACKEPOCH");
return;
}
ByteBuffer bbepoch = ByteBuffer.wrap(ackEpochPacket.getData());
ss = new StateSummary(bbepoch.getInt(), ackEpochPacket.getZxid());
// 等待半数参与者对生成epoch
leader.waitForEpochAck(this.getSid(), ss);
}
当leader向每个节点发送了带有最新epoch的LEADERINFO消息后，会等待过半learner发送对该epoch的ack消息
基本流程和getEpochToPropose类似
public void waitForEpochAck(long id, StateSummary ss) throws IOException, InterruptedException {
synchronized(electingFollowers) {
if (electionFinished) {
return;
}
if (ss.getCurrentEpoch() != -1) {
if (ss.isMoreRecentThan(leaderStateSummary)) {
throw new IOException("Follower is ahead of the leader, leader summary: "
+ leaderStateSummary.getCurrentEpoch()
+ " (current epoch), "
+ leaderStateSummary.getLastZxid()
+ " (last zxid)");
}
if (isParticipant(id)) {
electingFollowers.add(id);
}
}
QuorumVerifier verifier = self.getQuorumVerifier();
if (electingFollowers.contains(self.getId()) && verifier.containsQuorum(electingFollowers)) {
electionFinished = true;
electingFollowers.notifyAll();
} else {
long start = Time.currentElapsedTime();
long cur = start;
long end = start + self.getInitLimit()*self.getTickTime();
while(!electionFinished && cur < end) {
electingFollowers.wait(end - cur);
cur = Time.currentElapsedTime();
}
if (!electionFinished) {
throw new InterruptedException("Timeout while waiting for epoch to be acked by quorum");
}
}
}
}
同步数据
todo
boolean needSnap = syncFollower(peerLastZxid, leader.zk.getZKDatabase(), leader);
/* if we are not truncating or sending a diff just send a snapshot */
if (needSnap) {
boolean exemptFromThrottle = getLearnerType() != LearnerType.OBSERVER;
LearnerSnapshot snapshot =
leader.getLearnerSnapshotThrottler().beginSnapshot(exemptFromThrottle);
try {
long zxidToSend = leader.zk.getZKDatabase().getDataTreeLastProcessedZxid();
oa.writeRecord(new QuorumPacket(Leader.SNAP, zxidToSend, null, null), "packet");
bufferedOutput.flush();
LOG.info("Sending snapshot last zxid of peer is 0x{}, zxid of leader is 0x{}, "
+ "send zxid of db as 0x{}, {} concurrent snapshots, "
+ "snapshot was {} from throttle",
Long.toHexString(peerLastZxid),
Long.toHexString(leaderLastZxid),
Long.toHexString(zxidToSend),
snapshot.getConcurrentSnapshotNumber(),
snapshot.isEssential() ? "exempt" : "not exempt");
// Dump data to peer
leader.zk.getZKDatabase().serializeSnapshot(oa);
oa.writeString("BenWasHere", "signature");
bufferedOutput.flush();
} finally {
snapshot.close();
}
}
确认新leader
// LearnerHandler
public void run() {
// 生成NEWLEADER信息并发送给对端
QuorumPacket newLeaderQP = new QuorumPacket(Leader.NEWLEADER,
newLeaderZxid, leader.self.getLastSeenQuorumVerifier()
.toString().getBytes(), null);
queuedPackets.add(newLeaderQP);
bufferedOutput.flush();
// Start thread that blast packets in the queue to learner
startSendingPackets();
// 从对端输入流中读取数据
qp = new QuorumPacket();
ia.readRecord(qp, "packet");
if(qp.getType() != Leader.ACK){
LOG.error("Next packet was supposed to be an ACK,"
+ " but received packet: {}", packetToString(qp));
return;
}
if(LOG.isDebugEnabled()){
LOG.debug("Received NEWLEADER-ACK message from " + sid);
}
// 等待过半参与者对新leader的确认
leader.waitForNewLeaderAck(getSid(), qp.getZxid());
}
void lead() {
waitForNewLeaderAck(self.getId(), zk.getZxid());
}
当leader向其他learner发送了NEWLEADER消息后，会判断是否有过半的节点发送了对新领导者的确认信息
public void waitForNewLeaderAck(long sid, long zxid)
throws InterruptedException {
synchronized (newLeaderProposal.qvAcksetPairs) {
if (quorumFormed) {
return;
}
long currentZxid = newLeaderProposal.packet.getZxid();
if (zxid != currentZxid) {
LOG.error("NEWLEADER ACK from sid: " + sid
+ " is from a different epoch - current 0x"
+ Long.toHexString(currentZxid) + " receieved 0x"
+ Long.toHexString(zxid));
return;
}
/*
* Note that addAck already checks that the learner
* is a PARTICIPANT.
*/
newLeaderProposal.addAck(sid);
if (newLeaderProposal.hasAllQuorums()) {
quorumFormed = true;
newLeaderProposal.qvAcksetPairs.notifyAll();
} else {
long start = Time.currentElapsedTime();
long cur = start;
long end = start + self.getInitLimit() * self.getTickTime();
while (!quorumFormed && cur < end) {
newLeaderProposal.qvAcksetPairs.wait(end - cur);
cur = Time.currentElapsedTime();
}
if (!quorumFormed) {
throw new InterruptedException(
"Timeout while waiting for NEWLEADER to be acked by quorum");
}
}
}
}
启动ZookeeperServer
等待Leader启动ZookeeperServe
// Leader
void lead() {
startZkServer();
}
// LearnerHandler
public void run() {
synchronized(leader.zk){
while(!leader.zk.isRunning() && !this.isInterrupted()){
leader.zk.wait(20);
}
}
}
心跳
// Leader
void lead() {
// 一个tickTime中Leader会向其他节点发送两次ping信息
// 因此每两次循环会执行过半检查和递增时钟操作
while (true) {
synchronized (this) {
long start = Time.currentElapsedTime();
long cur = start;
// 半个tickTime
long end = start + self.tickTime / 2;
while (cur < end) {
wait(end - cur);
cur = Time.currentElapsedTime();
}
// 每两次循环递增时钟
if (!tickSkip) {
self.tick.incrementAndGet();
}
// We use an instance of SyncedLearnerTracker to
// track synced learners to make sure we still have a
// quorum of current (and potentially next pending) view.
SyncedLearnerTracker syncedAckSet = new SyncedLearnerTracker();
syncedAckSet.addQuorumVerifier(self.getQuorumVerifier());
if (self.getLastSeenQuorumVerifier() != null
&& self.getLastSeenQuorumVerifier().getVersion() > self
.getQuorumVerifier().getVersion()) {
syncedAckSet.addQuorumVerifier(self
.getLastSeenQuorumVerifier());
}
syncedAckSet.addAck(self.getId());
for (LearnerHandler f : getLearners()) {
// 判断当前时钟是否在tickOfNextAckDeadline之前，即最近接收过对端节点的信息
if (f.synced()) {
syncedAckSet.addAck(f.getSid());
}
}
// check leader running status
if (!this.isRunning()) {
// set shutdown flag
shutdownMessage = "Unexpected internal error";
break;
}
// 每两次循环，判断一下是否有过半节点仍然和当前节点保持着心跳
if (!tickSkip && !syncedAckSet.hasAllQuorums()) {
// Lost quorum of last committed and/or last proposed
// config, set shutdown flag
shutdownMessage = "Not sufficient followers synced, only synced with sids: [ "
+ syncedAckSet.ackSetsToString() + " ]";
break;
}
tickSkip = !tickSkip;
}
// 发送ping信息
for (LearnerHandler f : getLearners()) {
f.ping();
}
}
// 当没有过半节点和leader保持心跳时，会关闭leader，进入looking，重新开始选举
if (shutdownMessage != null) {
shutdown(shutdownMessage);
// leader goes in looking state
}
}
// LearnerHandler
public void ping() {
// If learner hasn't sync properly yet, don't send ping packet
// otherwise, the learner will crash
if (!sendingThreadStarted) {
return;
}
long id;
if (syncLimitCheck.check(System.nanoTime())) {
synchronized(leader) {
id = leader.lastProposed;
}
QuorumPacket ping = new QuorumPacket(Leader.PING, id, null, null);
queuePacket(ping);
} else {
LOG.warn("Closing connection to peer due to transaction timeout.");
shutdown();
}
}
// SyncLimitCheck
public synchronized boolean check(long time) {
if (currentTime == 0) {
return true;
} else {
long msDelay = (time - currentTime) / 1000000;
return (msDelay < (leader.self.tickTime * leader.self.syncLimit));
}
}
Follower
// QuorumPeer
public void run() {
case FOLLOWING:
try {
LOG.info("FOLLOWING");
setFollower(makeFollower(logFactory));
follower.followLeader();
} catch (Exception e) {
LOG.warn("Unexpected exception",e);
} finally {
follower.shutdown();
setFollower(null);
updateServerState();
}
break;
}
创建
// QuorumPeer
protected Follower makeFollower(FileTxnSnapLog logFactory) throws IOException {
return new Follower(this, new FollowerZooKeeperServer(logFactory, this, this.zkDb));
}
Follower(QuorumPeer self,FollowerZooKeeperServer zk) {
this.self = self;
this.zk=zk;
this.fzk = zk;
}
运行
// Follower
void followLeader() throws InterruptedException {
self.end_fle = Time.currentElapsedTime();
long electionTimeTaken = self.end_fle - self.start_fle;
self.setElectionTimeTaken(electionTimeTaken);
LOG.info("FOLLOWING - LEADER ELECTION TOOK - {} {}", electionTimeTaken,
QuorumPeer.FLE_TIME_UNIT);
self.start_fle = 0;
self.end_fle = 0;
fzk.registerJMX(new FollowerBean(this, zk), self.jmxLocalPeerBean);
try {
// 1. 通过投票结果获取当前leader的信息
QuorumServer leaderServer = findLeader();
try {
// 2. 连接leader
connectToLeader(leaderServer.addr, leaderServer.hostname);
// 3. 注册到leader
long newEpochZxid = registerWithLeader(Leader.FOLLOWERINFO);
if (self.isReconfigStateChange())
throw new Exception("learned about role change");
//check to see if the leader zxid is lower than ours
//this should never happen but is just a safety check
long newEpoch = ZxidUtils.getEpochFromZxid(newEpochZxid);
if (newEpoch < self.getAcceptedEpoch()) {
LOG.error("Proposed leader epoch " + ZxidUtils.zxidToString(newEpochZxid)
+ " is less than our accepted epoch " + ZxidUtils.zxidToString(self.getAcceptedEpoch()));
throw new IOException("Error: Epoch of leader is lower");
}
// 4. 同步leader
syncWithLeader(newEpochZxid);
QuorumPacket qp = new QuorumPacket();
while (this.isRunning()) {
// 从leader输入流中读取数据
readPacket(qp);
// 处理读取到的数据
processPacket(qp);
}
} catch (Exception e) {
LOG.warn("Exception when following the leader", e);
try {
sock.close();
} catch (IOException e1) {
e1.printStackTrace();
}
// clear pending revalidations
pendingRevalidations.clear();
}
} finally {
zk.unregisterJMX((Learner)this);
}
}
连接leader
// Follower
protected void connectToLeader(InetSocketAddress addr, String hostname)
throws IOException, InterruptedException, X509Exception {
// 创建socket连接
this.sock = createSocket();
// 建立连接的最长时间
int initLimitTime = self.tickTime * self.initLimit;
int remainingInitLimitTime = initLimitTime;
long startNanoTime = nanoTime();
// 重试连接
// 如果重试5次失败或者在initLimitTime内没有建立连接，连接失败
for (int tries = 0; tries < 5; tries++) {
try {
// recalculate the init limit time because retries sleep for 1000 milliseconds
remainingInitLimitTime = initLimitTime - (int)((nanoTime() - startNanoTime) / 1000000);
if (remainingInitLimitTime <= 0) {
LOG.error("initLimit exceeded on retries.");
throw new IOException("initLimit exceeded on retries.");
}
// 连接leader
sockConnect(sock, addr, Math.min(self.tickTime * self.syncLimit, remainingInitLimitTime));
if (self.isSslQuorum()) {
((SSLSocket) sock).startHandshake();
}
sock.setTcpNoDelay(nodelay);
break;
} catch (IOException e) {
// 连接失败，更新剩余时间
remainingInitLimitTime = initLimitTime - (int)((nanoTime() - startNanoTime) / 1000000);
if (remainingInitLimitTime <= 1000) {
LOG.error("Unexpected exception, initLimit exceeded. tries=" + tries +
", remaining init limit=" + remainingInitLimitTime +
", connecting to " + addr,e);
throw e;
} else if (tries >= 4) {
LOG.error("Unexpected exception, retries exceeded. tries=" + tries +
", remaining init limit=" + remainingInitLimitTime +
", connecting to " + addr,e);
throw e;
} else {
LOG.warn("Unexpected exception, tries=" + tries +
", remaining init limit=" + remainingInitLimitTime +
", connecting to " + addr,e);
this.sock = createSocket();
}
}
Thread.sleep(1000);
}
self.authLearner.authenticate(sock, hostname);
// 建立和leader的输入和输出流
leaderIs = BinaryInputArchive.getArchive(new BufferedInputStream(
sock.getInputStream()));
bufferedOutput = new BufferedOutputStream(sock.getOutputStream());
leaderOs = BinaryOutputArchive.getArchive(bufferedOutput);
}
注册信息
protected long registerWithLeader(int pktType) throws IOException{
// 1. 生成当前节点信息，id，协议版本，config版本
/*
* Send follower info, including last zxid and sid
*/
long lastLoggedZxid = self.getLastLoggedZxid();
QuorumPacket qp = new QuorumPacket();
qp.setType(pktType);
qp.setZxid(ZxidUtils.makeZxid(self.getAcceptedEpoch(), 0));
/*
* Add sid to payload
*/
LearnerInfo li = new LearnerInfo(self.getId(), 0x10000, self.getQuorumVerifier().getVersion());
ByteArrayOutputStream bsid = new ByteArrayOutputStream();
BinaryOutputArchive boa = BinaryOutputArchive.getArchive(bsid);
boa.writeRecord(li, "LearnerInfo");
qp.setData(bsid.toByteArray());
// 2. 发送给leader
writePacket(qp, true);
// 3. 接收leader发来的epoch通知请求
readPacket(qp);
// 从接收数据中解析出最新的epoch
final long newEpoch = ZxidUtils.getEpochFromZxid(qp.getZxid());
if (qp.getType() == Leader.LEADERINFO) {
// we are connected to a 1.0 server so accept the new epoch and read the next packet
leaderProtocolVersion = ByteBuffer.wrap(qp.getData()).getInt();
byte epochBytes[] = new byte[4];
final ByteBuffer wrappedEpochBytes = ByteBuffer.wrap(epochBytes);
// 使用新的epoch设置当前epoch
if (newEpoch > self.getAcceptedEpoch()) {
wrappedEpochBytes.putInt((int)self.getCurrentEpoch());
self.setAcceptedEpoch(newEpoch);
} else if (newEpoch == self.getAcceptedEpoch()) {
// since we have already acked an epoch equal to the leaders, we cannot ack
// again, but we still need to send our lastZxid to the leader so that we can
// sync with it if it does assume leadership of the epoch.
// the -1 indicates that this reply should not count as an ack for the new epoch
wrappedEpochBytes.putInt(-1);
} else {
throw new IOException("Leaders epoch, " + newEpoch + " is less than accepted epoch, " + self.getAcceptedEpoch());
}
// 4. 发送对epoch的响应信息
QuorumPacket ackNewEpoch = new QuorumPacket(Leader.ACKEPOCH, lastLoggedZxid, epochBytes, null);
writePacket(ackNewEpoch, true);
return ZxidUtils.makeZxid(newEpoch, 0);
} else {
if (newEpoch > self.getAcceptedEpoch()) {
self.setAcceptedEpoch(newEpoch);
}
if (qp.getType() != Leader.NEWLEADER) {
LOG.error("First packet should have been NEWLEADER");
throw new IOException("First packet should have been NEWLEADER");
}
return qp.getZxid();
}
}
同步数据
todo
循环处理请求
// Follower
public void followLeader() {
QuorumPacket qp = new QuorumPacket();
while (this.isRunning()) {
readPacket(qp);
processPacket(qp);
}
}
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