zk中ZooKeeperServer的作用是什么

zk中ZooKeeperServer的作用是什么，针对这个问题，这篇文章详细介绍了相对应的分析和解答，希望可以帮助更多想解决这个问题的小伙伴找到更简单易行的方法。

内部类

ChangeRecord 处理PrepRP和FinalRP之间的信息

static class ChangeRecord {    ChangeRecord(long zxid, String path, StatPersisted stat, int childCount, List acl) {        this.zxid = zxid;        this.path = path;        this.stat = stat;        this.childCount = childCount;        this.acl = acl;    }    long zxid;    String path;    StatPersisted stat; /* Make sure to create a new object when changing */    int childCount;    List acl; /* Make sure to create a new object when changing */    ChangeRecord duplicate(long zxid) {        StatPersisted stat = new StatPersisted();        if (this.stat != null) {            DataTree.copyStatPersisted(this.stat, stat);        }        return new ChangeRecord(zxid, path, stat, childCount, acl == null ? new ArrayList<>() : new ArrayList<>(acl));    }}protected enum State {    INITIAL,    RUNNING,    SHUTDOWN,    ERROR}初始化函数public ZooKeeperServer(FileTxnSnapLog txnLogFactory, int tickTime, int minSessionTimeout, int maxSessionTimeout, int clientPortListenBacklog, ZKDatabase zkDb, String initialConfig) {    serverStats = new ServerStats(this);    this.txnLogFactory = txnLogFactory;    this.txnLogFactory.setServerStats(this.serverStats);    this.zkDb = zkDb;    this.tickTime = tickTime;    setMinSessionTimeout(minSessionTimeout);    setMaxSessionTimeout(maxSessionTimeout);    this.listenBacklog = clientPortListenBacklog;    listener = new ZooKeeperServerListenerImpl(this);    readResponseCache = new ResponseCache();    connThrottle = new BlueThrottle();    this.initialConfig = initialConfig;    this.requestPathMetricsCollector = new RequestPathMetricsCollector();    this.initLargeRequestThrottlingSettings();    LOG.info("Created server with tickTime " + tickTime             + " minSessionTimeout " + getMinSessionTimeout()             + " maxSessionTimeout " + getMaxSessionTimeout()             + " clientPortListenBacklog " + getClientPortListenBacklog()             + " datadir " + txnLogFactory.getDataDir()             + " snapdir " + txnLogFactory.getSnapDir());}

通过参数构造一个数据管理Log FileTxnSnapLog

public ZooKeeperServer(File snapDir, File logDir, int tickTime) throws IOException {    this(new FileTxnSnapLog(snapDir, logDir), tickTime, "");}

集群和单机中加载数据

集群调用顺序

Leader#lead

ZooKeeperServer#loadData

单机调用顺序

ServerCnxFactory#startUp

ZooKeeperServer#startdata

ZooKeeperServer#loadData

单机版的startData方法

public void startdata() throws IOException, InterruptedException {    //check to see if zkDb is not null    if (zkDb == null) {        zkDb = new ZKDatabase(this.txnLogFactory);//实例化zkdatabase    }    if (!zkDb.isInitialized()) {        loadData();//没有初始化就重新初始化    }}

//加载数据public void loadData() throws IOException, InterruptedException {    /*     * When a new leader starts executing Leader#lead, it     * invokes this method. The database, however, has been     * initialized before running leader election so that     * the server could pick its zxid for its initial vote.     * It does it by invoking QuorumPeer#getLastLoggedZxid.     * Consequently, we don't need to initialize it once more     * and avoid the penalty of loading it a second time. Not     * reloading it is particularly important for applications     * that host a large database.     *     * The following if block checks whether the database has     * been initialized or not. Note that this method is     * invoked by at least one other method:     * ZooKeeperServer#startdata     */     //加载信息    if (zkDb.isInitialized()) {        setZxid(zkDb.getDataTreeLastProcessedZxid());    } else {        setZxid(zkDb.loadDataBase());    }    // Clean up dead sessions    //获取超时deadSessions    List deadSessions = new ArrayList<>();    for (Long session : zkDb.getSessions()) {        if (zkDb.getSessionWithTimeOuts().get(session) == null) {            deadSessions.add(session);        }    }    //杀掉session    for (long session : deadSessions) {        // TODO: Is lastProcessedZxid really the best thing to use?        killSession(session, zkDb.getDataTreeLastProcessedZxid());    }    // Make a clean snapshot 创建快照    takeSnapshot();}删除会话protected void killSession(long sessionId, long zxid) {    zkDb.killSession(sessionId, zxid);    if (LOG.isTraceEnabled()) {        ZooTrace.logTraceMessage(            LOG,            ZooTrace.SESSION_TRACE_MASK,            "ZooKeeperServer --- killSession: 0x" + Long.toHexString(sessionId));    }    if (sessionTracker != null) {        sessionTracker.removeSession(sessionId);    }}public synchronized void startup() {    if (sessionTracker == null) {        createSessionTracker();    }    //责任链处理    startSessionTracker();    //设置请求处理器    setupRequestProcessors();    startRequestThrottler();    //注册jmx    registerJMX();    startJvmPauseMonitor();    registerMetrics();    //设置状态    setState(State.RUNNING);    requestPathMetricsCollector.start();    localSessionEnabled = sessionTracker.isLocalSessionsEnabled();    notifyAll();}

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