zookeeper源码(07)leader、follower和observer
Leader
构造方法
public Leader(QuorumPeer self, LeaderZooKeeperServer zk) throws IOException {
this.self = self;
this.proposalStats = new BufferStats();
// 获取节点间通信地址
Set<InetSocketAddress> addresses;
if (self.getQuorumListenOnAllIPs()) {
addresses = self.getQuorumAddress().getWildcardAddresses();
} else {
addresses = self.getQuorumAddress().getAllAddresses();
}
// 创建ServerSocket并bind地址，add到serverSockets集，启动LearnerCnxAcceptor时使用
addresses.stream()
.map(address -> createServerSocket(address, self.shouldUsePortUnification(), self.isSslQuorum()))
.filter(Optional::isPresent)
.map(Optional::get)
.forEach(serverSockets::add);
this.zk = zk;
}
lead方法
QuorumPeer使用lead方法启动leader节点，从lead方法入手分析leader流程并分析重要的方法：
void lead() throws IOException, InterruptedException {
self.end_fle = Time.currentElapsedTime();
long electionTimeTaken = self.end_fle - self.start_fle;
self.setElectionTimeTaken(electionTimeTaken);
ServerMetrics.getMetrics().ELECTION_TIME.add(electionTimeTaken);
self.start_fle = 0;
self.end_fle = 0;
zk.registerJMX(new LeaderBean(this, zk), self.jmxLocalPeerBean);
try {
self.setZabState(QuorumPeer.ZabState.DISCOVERY);
self.tick.set(0);
// 使用ZooKeeperServer的loadData方法加载db数据
// 加载数据、清理session、生成快照(takeSnapshot)
zk.loadData();
leaderStateSummary = new StateSummary(self.getCurrentEpoch(), zk.getLastProcessedZxid());
// 启动线程接收Learner连接，创建LearnerHandler与客户端通信
cnxAcceptor = new LearnerCnxAcceptor();
cnxAcceptor.start();
// 获取上一次同步最终epoch并计算本次的epoch和zxid
long epoch = getEpochToPropose(self.getMyId(), self.getAcceptedEpoch());
// 设置新的zxid
zk.setZxid(ZxidUtils.makeZxid(epoch, 0));
synchronized (this) {
lastProposed = zk.getZxid();
}
newLeaderProposal.packet = new QuorumPacket(NEWLEADER, zk.getZxid(), null, null);
QuorumVerifier lastSeenQV = self.getLastSeenQuorumVerifier();
QuorumVerifier curQV = self.getQuorumVerifier();
if (curQV.getVersion() == 0 && curQV.getVersion() == lastSeenQV.getVersion()) {
// qv.version == 0
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());
}
// 等待足够数量的ACKEPOCH数据包，表示follower确认newEpoch
// follower会把lastLoggedZxid、currentEpoch发送过来，leader用这些参数判断同步数据的方式
waitForEpochAck(self.getMyId(), leaderStateSummary);
self.setCurrentEpoch(epoch); // 设置新的currentEpoch
self.setLeaderAddressAndId(self.getQuorumAddress(), self.getMyId());
self.setZabState(QuorumPeer.ZabState.SYNCHRONIZATION);
try {
// 等待follower的newLeaderAck
waitForNewLeaderAck(self.getMyId(), zk.getZxid());
} catch (InterruptedException e) {
// 略
return;
}
// 启动zookeeperServer
startZkServer();
self.setZabState(QuorumPeer.ZabState.BROADCAST);
self.adminServer.setZooKeeperServer(zk);
// We ping twice a tick, so we only update the tick every other iteration
boolean tickSkip = true;
String shutdownMessage = null;
while (true) {
synchronized (this) {
long start = Time.currentElapsedTime();
long cur = start;
long end = start + self.tickTime / 2;
// 等待tickTime / 2毫秒
while (cur < end) {
wait(end - cur);
cur = Time.currentElapsedTime();
}
if (!tickSkip) {
self.tick.incrementAndGet();
}
// 用来判断learner同步状态
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.getMyId());
// 查询learner的ack状态
for (LearnerHandler f : getLearners()) {
if (f.synced()) {
syncedAckSet.addAck(f.getSid());
}
}
if (!this.isRunning()) { // shutdown
break;
}
// 判断超半数learner已是同步状态
// 1个tickTime周期判断一次
if (!tickSkip && !syncedAckSet.hasAllQuorums() &&
!(self.getQuorumVerifier().overrideQuorumDecision(getForwardingFollowers()) &&
self.getQuorumVerifier().revalidateOutstandingProp(
this, new ArrayList<>(outstandingProposals.values()), lastCommitted))) {
// Lost quorum of last committed and/or last proposed
shutdownMessage = "Not sufficient followers synced";
break;
}
tickSkip = !tickSkip;
}
// ping learner
// 1个tickTime周期ping两次
for (LearnerHandler f : getLearners()) {
f.ping();
}
}
if (shutdownMessage != null) {
// leader goes in looking state
shutdown(shutdownMessage);
}
} finally {
zk.unregisterJMX(this);
}
}
getEpochToPropose方法
获取上一次同步的最终epoch并计算zxid的值：
public long getEpochToPropose(long sid, long lastAcceptedEpoch) throws InterruptedException, IOException {
synchronized (connectingFollowers) {
if (!waitingForNewEpoch) {
return epoch;
}
if (lastAcceptedEpoch >= epoch) {
epoch = lastAcceptedEpoch + 1; // 更新最新epoch
}
if (isParticipant(sid)) {
connectingFollowers.add(sid);
}
QuorumVerifier verifier = self.getQuorumVerifier();
// 连接的follower超过了半数
if (connectingFollowers.contains(self.getMyId()) && verifier.containsQuorum(connectingFollowers)) {
waitingForNewEpoch = false;
self.setAcceptedEpoch(epoch); // 设置新的epoch
connectingFollowers.notifyAll();
} else {
long start = Time.currentElapsedTime();
if (sid == self.getMyId()) {
timeStartWaitForEpoch = start;
}
long cur = start;
long end = start + self.getInitLimit() * self.getTickTime();
// 等待initLimit*tickTime毫秒，如果还是waitingForNewEpoch状态抛错，会触发重新选举
while (waitingForNewEpoch && cur < end && !quitWaitForEpoch) {
connectingFollowers.wait(end - cur);
cur = Time.currentElapsedTime();
}
if (waitingForNewEpoch) {
throw new InterruptedException("Timeout while waiting for epoch from quorum");
}
}
return epoch;
}
}
waitForEpochAck方法
等待足够数量的ACKEPOCH数据包，表示follower确认newEpoch，follower会把lastLoggedZxid、currentEpoch发送过来，leader用这些参数判断同步数据的方式：
public void waitForEpochAck(long id, StateSummary ss) throws IOException, InterruptedException {
synchronized (electingFollowers) {
if (electionFinished) {
return;
}
// 略
QuorumVerifier verifier = self.getQuorumVerifier();
if (electingFollowers.contains(self.getMyId()) && 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");
}
}
}
}
waitForNewLeaderAck方法
等待足够数量的Leader.ACK请求上来，之后才能开始正常通信：
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: {} is from a different epoch - current 0x{} received 0x{}",
sid, Long.toHexString(currentZxid), 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");
}
}
}
}
LearnerCnxAcceptor类
启动LearnerCnxAcceptor线程：
// Start thread that waits for connection requests from new followers.
cnxAcceptor = new LearnerCnxAcceptor();
cnxAcceptor.start();
LearnerCnxAcceptor类：
public void run() {
if (!stop.get() && !serverSockets.isEmpty()) {
ExecutorService executor = Executors.newFixedThreadPool(serverSockets.size());
CountDownLatch latch = new CountDownLatch(serverSockets.size());
// 启动LearnerCnxAcceptorHandler
serverSockets.forEach(serverSocket ->
executor.submit(new LearnerCnxAcceptorHandler(serverSocket, latch)));
try {
latch.await();
} catch (InterruptedException ie) {
} finally {
// 关闭连接、线程池
}
}
}
LearnerCnxAcceptorHandler类启动监听，接受连接：
class LearnerCnxAcceptorHandler implements Runnable {
private ServerSocket serverSocket;
private CountDownLatch latch;
LearnerCnxAcceptorHandler(ServerSocket serverSocket, CountDownLatch latch) {
this.serverSocket = serverSocket;
this.latch = latch;
}
@Override
public void run() {
try {
while (!stop.get()) {
acceptConnections(); // 接受连接
}
} catch (Exception e) {
// 关闭
} finally {
latch.countDown(); // countdown到0会唤醒LearnerCnxAcceptor
}
}
private void acceptConnections() throws IOException {
Socket socket = null;
boolean error = false;
try {
socket = serverSocket.accept(); // 接受客户端连接
socket.setSoTimeout(self.tickTime * self.initLimit); // timeout
socket.setTcpNoDelay(nodelay);
BufferedInputStream is = new BufferedInputStream(socket.getInputStream());
// 封装LearnerHandler对象，与客户端通信
LearnerHandler fh = new LearnerHandler(socket, is, Leader.this);
fh.start();
} catch (Exception e) {
// 略
} finally {
// 略
}
}
}
LearnerHandler
与客户端通信。
关键字段
protected final Socket sock; // 客户端socket
// Leader对象
final LearnerMaster learnerMaster;
// 给learner的唯一标识
protected long sid = 0;
// 发送队列
final LinkedBlockingQueue<QuorumPacket> queuedPackets = new LinkedBlockingQueue<>();
// zxid
protected volatile long lastZxid = -1;
// 输出输入流
private BinaryInputArchive ia;
private BinaryOutputArchive oa;
private final BufferedInputStream bufferedInput;
private BufferedOutputStream bufferedOutput;
// learner类型 PARTICIPANT/OBSERVER
private LearnerType learnerType = LearnerType.PARTICIPANT;
run方法
-
接收Leader.FOLLOWERINFO或Leader.OBSERVERINFO数据包，解析type、sid等关键字段，计算newEpoch和newLeaderZxid
-
发送Leader.LEADERINFO数据包，包含newLeaderZxid值
-
读取Leader.ACKEPOCH数据包，解析对端的epoch、zxid
-
根据对端zxid判断是否需要同步数据、如何同步数据(txnlog/committedlog/snapshot)
peerLastZxid = ss.getLastZxid(); // 对端最新processZxid // 同步txnlog或committedlog数据，或者返回true使用SNAP方式同步快照数据 boolean needSnap = syncFollower(peerLastZxid, learnerMaster); // 比对maxCommittedLog、minCommittedLog与peerLastZxid同步txnlog和committedlog数据或者使用SNAP同步数据 // committedlog在内存里面，性能更好 -
同步txnlog和committedlog数据
if ((maxCommittedLog >= peerLastZxid) && (minCommittedLog <= peerLastZxid)) { // 对端lastZxid在minCommittedLog和maxCommittedLog之间 // 直接使用committedlog同步 Iterator<Proposal> itr = db.getCommittedLog().iterator(); currentZxid = queueCommittedProposals(itr, peerLastZxid, null, maxCommittedLog); needSnap = false; } else if (peerLastZxid < minCommittedLog && txnLogSyncEnabled) { // 使用txnlog和committedLog同步 // 默认"最新snapshot文件字节数 * 0.33" long sizeLimit = db.calculateTxnLogSizeLimit(); // 从txnlog查找数据，当数据字节数大于sizeLimit将返回空集，强制使用SNAP同步 Iterator<Proposal> txnLogItr = db.getProposalsFromTxnLog(peerLastZxid, sizeLimit); if (txnLogItr.hasNext()) { // 使用txnlog同步 currentZxid = queueCommittedProposals(txnLogItr, peerLastZxid, minCommittedLog, maxCommittedLog); // txnlog同步未达到minCommittedLog表示txnlog和committedLog数据存在缺失 // 将强制使用SNAP同步 if (currentZxid < minCommittedLog) { currentZxid = peerLastZxid; // Clear out currently queued requests and revert to sending a snapshot queuedPackets.clear(); needOpPacket = true; } else { // 使用committedlog同步 Iterator<Proposal> committedLogItr = db.getCommittedLog().iterator(); currentZxid = queueCommittedProposals(committedLogItr, currentZxid, null, maxCommittedLog); needSnap = false; } } // 略 } -
启动转发功能
// Start forwarding leaderLastZxid = learnerMaster.startForwarding(this, currentZxid); // 把toBeApplied数据(待commit状态)发出去 // 添加到forwardingFollowers/observingLearners集 -
如果needSnap为true则需要发送SNAP请求让learner读取输入流加载dataTree
long zxidToSend = learnerMaster.getZKDatabase().getDataTreeLastProcessedZxid(); // 发送SNAP请求 oa.writeRecord(new QuorumPacket(Leader.SNAP, zxidToSend, null, null), "packet"); messageTracker.trackSent(Leader.SNAP); bufferedOutput.flush(); // 将dataTree序列化发给learner learnerMaster.getZKDatabase().serializeSnapshot(oa); oa.writeString("BenWasHere", "signature"); bufferedOutput.flush(); -
发送NEWLEADER请求
if (getVersion() < 0x10000) { QuorumPacket newLeaderQP = new QuorumPacket(Leader.NEWLEADER, newLeaderZxid, null, null); oa.writeRecord(newLeaderQP, "packet"); } else { QuorumPacket newLeaderQP = new QuorumPacket( Leader.NEWLEADER, newLeaderZxid, learnerMaster.getQuorumVerifierBytes(), null); queuedPackets.add(newLeaderQP); } -
启动sendPackets线程：从queuedPackets取消息发给learner节点
-
等待NEWLEADER ACK响应
qp = new QuorumPacket();
ia.readRecord(qp, "packet");
messageTracker.trackReceived(qp.getType());
if (qp.getType() != Leader.ACK) {
return;
}
learnerMaster.waitForNewLeaderAck(getSid(), qp.getZxid());
-
等待zookeeperServer启动完成
-
发送UPTODATE请求，告知follower处于最新状态，并且可以开始响应客户端
queuedPackets.add(new QuorumPacket(Leader.UPTODATE, -1, null, null)); -
启动while循环与客户端保持通信，处理ACK、PING、REVALIDATE、REQUEST等请求
Follower
包含了follower的逻辑。
followLeader方法
the main method called by the follower to follow the leader.
void followLeader() throws InterruptedException {
self.end_fle = Time.currentElapsedTime();
long electionTimeTaken = self.end_fle - self.start_fle;
self.setElectionTimeTaken(electionTimeTaken);
ServerMetrics.getMetrics().ELECTION_TIME.add(electionTimeTaken);
self.start_fle = 0;
self.end_fle = 0;
fzk.registerJMX(new FollowerBean(this, zk), self.jmxLocalPeerBean);
long connectionTime = 0;
boolean completedSync = false;
try {
self.setZabState(QuorumPeer.ZabState.DISCOVERY);
// 查找leader服务器
QuorumServer leaderServer = findLeader();
try {
// 连接leader服务器
connectToLeader(leaderServer.addr, leaderServer.hostname);
connectionTime = System.currentTimeMillis();
// 获取事务id
long newEpochZxid = registerWithLeader(Leader.FOLLOWERINFO);
if (self.isReconfigStateChange()) {
throw new Exception("learned about role change");
}
// zxid >> 32L得到epoch
long newEpoch = ZxidUtils.getEpochFromZxid(newEpochZxid);
if (newEpoch < self.getAcceptedEpoch()) {
throw new IOException("Error: Epoch of leader is lower");
}
long startTime = Time.currentElapsedTime();
self.setLeaderAddressAndId(leaderServer.addr, leaderServer.getId());
self.setZabState(QuorumPeer.ZabState.SYNCHRONIZATION);
// 与leader同步数据
syncWithLeader(newEpochZxid);
self.setZabState(QuorumPeer.ZabState.BROADCAST);
completedSync = true;
long syncTime = Time.currentElapsedTime() - startTime;
ServerMetrics.getMetrics().FOLLOWER_SYNC_TIME.add(syncTime);
if (self.getObserverMasterPort() > 0) {
// 创建ObserverMaster用来链式复制，此处不做分析
om = new ObserverMaster(self, fzk, self.getObserverMasterPort());
om.start();
} else {
om = null;
}
// 保持通信
QuorumPacket qp = new QuorumPacket();
while (this.isRunning()) {
readPacket(qp);
processPacket(qp); // 处理leader的数据包
}
} catch (Exception e) {
// ...
}
} finally {
// ...
}
}
connectToLeader方法
protected void connectToLeader(MultipleAddresses multiAddr, String hostname) throws IOException {
this.leaderAddr = multiAddr;
Set<InetSocketAddress> addresses;
if (self.isMultiAddressReachabilityCheckEnabled()) {
addresses = multiAddr.getAllReachableAddressesOrAll();
} else {
addresses = multiAddr.getAllAddresses();
}
ExecutorService executor = Executors.newFixedThreadPool(addresses.size());
CountDownLatch latch = new CountDownLatch(addresses.size());
AtomicReference<Socket> socket = new AtomicReference<>(null);
// 使用LeaderConnector异步建立连接，此处考虑到了多地址的情况
addresses.stream()
.map(address -> new LeaderConnector(address, socket, latch)).forEach(executor::submit);
try {
latch.await();
} catch (InterruptedException e) {
} finally {
// 关闭executor
}
if (socket.get() == null) {
throw new IOException("Failed connect to " + multiAddr);
} else {
sock = socket.get();
sockBeingClosed.set(false);
}
// 认证 略
self.authLearner.authenticate(sock, hostname);
// 获取输入输出流
leaderIs = BinaryInputArchive.getArchive(new BufferedInputStream(sock.getInputStream()));
bufferedOutput = new BufferedOutputStream(sock.getOutputStream());
leaderOs = BinaryOutputArchive.getArchive(bufferedOutput);
// 启动发送线程，基于BlockingQueue的生产者消费者模式
if (asyncSending) {
startSendingThread();
}
}
registerWithLeader方法
protected long registerWithLeader(int pktType) throws IOException {
// 1. 先发送一个Leader.FOLLOWERINFO类型数据包:
// Leader.FOLLOWERINFO, zxid, sid, protocolVersion, quorumVersion
long lastLoggedZxid = self.getLastLoggedZxid();
QuorumPacket qp = new QuorumPacket();
qp.setType(pktType);
qp.setZxid(ZxidUtils.makeZxid(self.getAcceptedEpoch(), 0));
LearnerInfo li = new LearnerInfo(self.getMyId(), 0x10000, self.getQuorumVerifier().getVersion());
ByteArrayOutputStream bsid = new ByteArrayOutputStream();
BinaryOutputArchive boa = BinaryOutputArchive.getArchive(bsid);
boa.writeRecord(li, "LearnerInfo");
qp.setData(bsid.toByteArray());
writePacket(qp, true); // 把数据包写出去
// 2. 读取leader的Leader.LEADERINFO数据包
readPacket(qp);
final long newEpoch = ZxidUtils.getEpochFromZxid(qp.getZxid()); // 解析newEpoch
if (qp.getType() == Leader.LEADERINFO) { // 使用1.0版本协议
leaderProtocolVersion = ByteBuffer.wrap(qp.getData()).getInt();
byte[] epochBytes = new byte[4];
final ByteBuffer wrappedEpochBytes = ByteBuffer.wrap(epochBytes);
if (newEpoch > self.getAcceptedEpoch()) {
wrappedEpochBytes.putInt((int) self.getCurrentEpoch());
self.setAcceptedEpoch(newEpoch); // 设置acceptEpoch
} else if (newEpoch == self.getAcceptedEpoch()) {
wrappedEpochBytes.putInt(-1);
} else {
throw new IOException("...");
}
// 3. 发送ACKEPOCH类型数据包:
// 包含self.lastLoggedZxid和self.currentEpoch
QuorumPacket ackNewEpoch = new QuorumPacket(Leader.ACKEPOCH, lastLoggedZxid, epochBytes, null);
writePacket(ackNewEpoch, true);
return ZxidUtils.makeZxid(newEpoch, 0);
} else {
// 低版本分支，略
}
}
syncWithLeader方法
-
读leader数据包
-
DIFF - 表示数据已经是最新，可以直接同步新数据
-
SNAP - 将leader输入流(leader的dataTree快照数据)反序列化到zkDb
zk.getZKDatabase().deserializeSnapshot(leaderIs); zk.getZKDatabase().setlastProcessedZxid(qp.getZxid()); -
TRUNC - 将数据truncate到指定位置
boolean truncated = zk.getZKDatabase().truncateLog(qp.getZxid()); zk.getZKDatabase().setlastProcessedZxid(qp.getZxid());
-
-
继续读leader数据包，leader可能使用txnlog或committedlog同步数据
-
同步数据并提交：
-
PROPOSAL - 提案数据会放入packetsNotCommitted集待处理
-
COMMIT/COMMITANDACTIVATE - 提交数据会放入packetsCommitted集待处理
-
INFORM/INFORMANDACTIVATE - 同上
-
NEWLEADER - leader已经停止同步数据，follower会takeSnapshot、setCurrentEpoch、将packetsNotCommitted都提交给zk、响应ACK
// fzk.logRequest(p.hdr, p.rec, p.digest); public void logRequest(TxnHeader hdr, Record txn, TxnDigest digest) { Request request = new Request( hdr.getClientId(), hdr.getCxid(), hdr.getType(), hdr, txn, hdr.getZxid()); request.setTxnDigest(digest); if ((request.zxid & 0xffffffffL) != 0) { pendingTxns.add(request); // 待处理的事务集 } syncProcessor.processRequest(request); // 持久化磁盘 } -
UPTODATE - leader会等待足够的follower响应ACK并且确定各种组件已启动之后，发送一个UPTODATE数据包，表示follower已经处于同步状态，停止同步，跳出循环
-
-
处理packetsNotCommitted和packetsCommitted集，处理事务或写磁盘
FollowerZooKeeperServer fzk = (FollowerZooKeeperServer) zk; for (PacketInFlight p : packetsNotCommitted) { fzk.logRequest(p.hdr, p.rec, p.digest); } for (Long zxid : packetsCommitted) { fzk.commit(zxid); } // 使用RequestProcessor处理Request // 后续再详细介绍 -
Observer会执行下面代码处理
ObserverZooKeeperServer ozk = (ObserverZooKeeperServer) zk; for (PacketInFlight p : packetsNotCommitted) { Long zxid = packetsCommitted.peekFirst(); if (p.hdr.getZxid() != zxid) { // log warning message if there is no matching commit // old leader send outstanding proposal to observer continue; } packetsCommitted.remove(); Request request = new Request( p.hdr.getClientId(), p.hdr.getCxid(), p.hdr.getType(), p.hdr, p.rec, -1); request.setTxnDigest(p.digest); ozk.commitRequest(request); }
processPacket方法
在连接建立、数据处于同步状态后，follower会阻塞读取来自leader的数据包，之后使用processPacket方法处理：
// create a reusable packet to reduce gc impact
QuorumPacket qp = new QuorumPacket();
while (this.isRunning()) {
readPacket(qp);
processPacket(qp);
}
processPacket方法：
protected void processPacket(QuorumPacket qp) throws Exception {
switch (qp.getType()) {
case Leader.PING:
ping(qp);
break;
case Leader.PROPOSAL:
ServerMetrics.getMetrics().LEARNER_PROPOSAL_RECEIVED_COUNT.add(1);
TxnLogEntry logEntry = SerializeUtils.deserializeTxn(qp.getData());
TxnHeader hdr = logEntry.getHeader();
Record txn = logEntry.getTxn();
TxnDigest digest = logEntry.getDigest();
if (hdr.getZxid() != lastQueued + 1) {
LOG.warn("Got zxid 0x{} expected 0x{}",
Long.toHexString(hdr.getZxid()), Long.toHexString(lastQueued + 1));
}
lastQueued = hdr.getZxid();
if (hdr.getType() == OpCode.reconfig) {
SetDataTxn setDataTxn = (SetDataTxn) txn;
QuorumVerifier qv = self.configFromString(new String(setDataTxn.getData(), UTF_8));
self.setLastSeenQuorumVerifier(qv, true);
}
// 封装Request使用syncProcessor.processRequest(request)写磁盘
fzk.logRequest(hdr, txn, digest);
// 略
break;
case Leader.COMMIT:
ServerMetrics.getMetrics().LEARNER_COMMIT_RECEIVED_COUNT.add(1);
// 使用commitProcessor.commit(request)提交请求
fzk.commit(qp.getZxid());
// 略
break;
case Leader.COMMITANDACTIVATE:
// get the new configuration from the request
Request request = fzk.pendingTxns.element();
SetDataTxn setDataTxn = (SetDataTxn) request.getTxn();
QuorumVerifier qv = self.configFromString(new String(setDataTxn.getData(), UTF_8));
// get new designated leader from (current) leader's message
ByteBuffer buffer = ByteBuffer.wrap(qp.getData());
long suggestedLeaderId = buffer.getLong();
final long zxid = qp.getZxid();
boolean majorChange = self.processReconfig(qv, suggestedLeaderId, zxid, true);
// commit (writes the new config to ZK tree (/zookeeper/config)
fzk.commit(zxid);
// 略
break;
case Leader.UPTODATE:
// 正常情况下主从复制数据不应该出现这种类型数据包
break;
case Leader.REVALIDATE:
if (om == null || !om.revalidateLearnerSession(qp)) {
revalidate(qp);
}
break;
case Leader.SYNC:
fzk.sync();
break;
default:
LOG.warn("Unknown packet type: {}", LearnerHandler.packetToString(qp));
break;
}
}
Observer
observeLeader方法
void observeLeader() throws Exception {
zk.registerJMX(new ObserverBean(this, zk), self.jmxLocalPeerBean);
long connectTime = 0;
boolean completedSync = false;
try {
self.setZabState(QuorumPeer.ZabState.DISCOVERY);
// 获取leader或一个observerMaster服务器
QuorumServer master = findLearnerMaster();
try {
// 连接leader或observerMaster
connectToLeader(master.addr, master.hostname);
connectTime = System.currentTimeMillis();
long newLeaderZxid = registerWithLeader(Leader.OBSERVERINFO);
if (self.isReconfigStateChange()) {
throw new Exception("learned about role change");
}
final long startTime = Time.currentElapsedTime();
self.setLeaderAddressAndId(master.addr, master.getId());
self.setZabState(QuorumPeer.ZabState.SYNCHRONIZATION);
syncWithLeader(newLeaderZxid);
self.setZabState(QuorumPeer.ZabState.BROADCAST);
completedSync = true;
final long syncTime = Time.currentElapsedTime() - startTime;
ServerMetrics.getMetrics().OBSERVER_SYNC_TIME.add(syncTime);
QuorumPacket qp = new QuorumPacket();
while (this.isRunning() && nextLearnerMaster.get() == null) {
readPacket(qp);
processPacket(qp);
}
} catch (Exception e) {
closeSocket();
// clear pending revalidations
pendingRevalidations.clear();
}
} finally {
currentLearnerMaster = null;
zk.unregisterJMX(this);
if (connectTime != 0) {
long connectionDuration = System.currentTimeMillis() - connectTime;
messageTracker.dumpToLog(leaderAddr.toString());
}
}
}
processPacket方法
protected void processPacket(QuorumPacket qp) throws Exception {
TxnLogEntry logEntry;
TxnHeader hdr;
TxnDigest digest;
Record txn;
switch (qp.getType()) {
case Leader.PING:
ping(qp);
break;
case Leader.PROPOSAL:
LOG.warn("Ignoring proposal");
break;
case Leader.COMMIT:
LOG.warn("Ignoring commit");
break;
case Leader.UPTODATE:
LOG.error("Received an UPTODATE message after Observer started");
break;
case Leader.REVALIDATE:
revalidate(qp);
break;
case Leader.SYNC:
((ObserverZooKeeperServer) zk).sync();
break;
case Leader.INFORM:
ServerMetrics.getMetrics().LEARNER_COMMIT_RECEIVED_COUNT.add(1);
logEntry = SerializeUtils.deserializeTxn(qp.getData());
hdr = logEntry.getHeader();
txn = logEntry.getTxn();
digest = logEntry.getDigest();
Request request = new Request(hdr.getClientId(), hdr.getCxid(), hdr.getType(), hdr, txn, 0);
request.logLatency(ServerMetrics.getMetrics().COMMIT_PROPAGATION_LATENCY);
request.setTxnDigest(digest);
ObserverZooKeeperServer obs = (ObserverZooKeeperServer) zk;
obs.commitRequest(request); // 提交
break;
case Leader.INFORMANDACTIVATE:
// reconfig功能使用
break;
default:
LOG.warn("Unknown packet type: {}", LearnerHandler.packetToString(qp));
break;
}
}
Leader与Follower通信总结
Leader Follower
FOLLOWERINFO/OBSERVERINFO数据包发送acceptEpoch
<-------------------------------------------------------------------
leader计算newEpoch、newZxid
LEADERINFO数据包发送最新的zxid
------------------------------------------------------------------->
follower接受newEpoch
ACKEPOCH数据包发送lastLoggedZxid、currentEpoch
<------------------------------------------------------------------
leader确定数据同步方式
DIFF/TRUNC/SNAP或者同步数据(loop)
------------------------------------------------------------------->
NEWLEADER数据包
------------------------------------------------------------------->
ACK数据包
<------------------------------------------------------------------
UPTODATE数据包
------------------------------------------------------------------->
PROPOSAL数据包
------------------------------------------------------------------->
ACK数据包
<------------------------------------------------------------------
COMMIT数据包
------------------------------------------------------------------->
ACK数据包
<------------------------------------------------------------------
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