diff --git a/hdfs/dataNode启动过程.md b/hdfs/dataNode启动过程.md new file mode 100644 index 0000000..7907308 --- /dev/null +++ b/hdfs/dataNode启动过程.md @@ -0,0 +1,226 @@ + +# 启动 + +## createDataNode + +DataNode核心启动类是从createDataNode开始的。 + +```java +public static DataNode createDataNode(String args[], Configuration conf, + SecureResources resources) throws IOException { + // 初始化DataNode,核心函数在makeInstance里面的new DataNode()进行初始化。 + DataNode dn = instantiateDataNode(args, conf, resources); + if (dn != null) { + // 启动DataNode + dn.runDatanodeDaemon(); + } + return dn; +} +``` + +### makeInstance + +```java +static DataNode makeInstance(Collection dataDirs, + Configuration conf, SecureResources resources) throws IOException { + List locations; + StorageLocationChecker storageLocationChecker = + new StorageLocationChecker(conf, new Timer()); + try { + // 对存储路径进行检查。返回可用的位置。 + locations = storageLocationChecker.check(conf, dataDirs); + } catch (InterruptedException ie) { + throw new IOException("Failed to instantiate DataNode", ie); + } + DefaultMetricsSystem.initialize("DataNode"); + + assert locations.size() > 0 : "number of data directories should be > 0"; + // 初始化DataNode实例。在构造函数里面startDataNode比较重要，是启动DataNode的核心函数，需要重点关注。 + return new DataNode(conf, locations, storageLocationChecker, resources); +} +``` + +### startDataNode + + +```java +void startDataNode(List dataDirectories, + SecureResources resources + ) throws IOException { + + // settings global for all BPs in the Data Node + this.secureResources = resources; + synchronized (this) { + this.dataDirs = dataDirectories; + } + this.dnConf = new DNConf(this); + checkSecureConfig(dnConf, getConf(), resources); + // ... 省略 .... + + storage = new DataStorage(); + + // global DN settings + registerMXBean(); + // 初始化dataXceiver服务：用于DN接受客户端和其他DN发送过来的数据的服务。 + initDataXceiver(); + // 初始化HTTP服务。 + startInfoServer(); + //TODO 待定。 + pauseMonitor = new JvmPauseMonitor(); + pauseMonitor.init(getConf()); + pauseMonitor.start(); + + // BlockPoolTokenSecretManager is required to create ipc server. + this.blockPoolTokenSecretManager = new BlockPoolTokenSecretManager(); + + // Login is done by now. Set the DN user name. + dnUserName = UserGroupInformation.getCurrentUser().getUserName(); + LOG.info("dnUserName = {}", dnUserName); + LOG.info("supergroup = {}", supergroup); + // 初始化DN的RPC调用服务。 + initIpcServer(); + + metrics = DataNodeMetrics.create(getConf(), getDisplayName()); + peerMetrics = dnConf.peerStatsEnabled ? + DataNodePeerMetrics.create(getDisplayName(), getConf()) : null; + metrics.getJvmMetrics().setPauseMonitor(pauseMonitor); + + ecWorker = new ErasureCodingWorker(getConf(), this); + blockRecoveryWorker = new BlockRecoveryWorker(this); + + blockPoolManager = new BlockPoolManager(this); + // DN向NN注册，其中核心的函数为doRefreshNamenodes + blockPoolManager.refreshNamenodes(getConf()); + + // Create the ReadaheadPool from the DataNode context so we can + // exit without having to explicitly shutdown its thread pool. + readaheadPool = ReadaheadPool.getInstance(); + saslClient = new SaslDataTransferClient(dnConf.getConf(), + dnConf.saslPropsResolver, dnConf.trustedChannelResolver); + saslServer = new SaslDataTransferServer(dnConf, blockPoolTokenSecretManager); + startMetricsLogger(); + + if (dnConf.diskStatsEnabled) { + diskMetrics = new DataNodeDiskMetrics(this, + dnConf.outliersReportIntervalMs, getConf()); + } +} +``` + +### doRefreshNamenodes + +主要是向NN注册当前DN。 + + +```java +private void doRefreshNamenodes( + Map> addrMap, + Map> lifelineAddrMap) + throws IOException { + + Set toRefresh = Sets.newLinkedHashSet(); + Set toAdd = Sets.newLinkedHashSet(); + Set toRemove; + + synchronized (this) { + // Step 1. For each of the new nameservices, figure out whether + // it's an update of the set of NNs for an existing NS, + // or an entirely new nameservice. + // 判断当前DN中的nameservice是否已经存在：如果已经存在则需要刷新；否则需要添加。 + for (String nameserviceId : addrMap.keySet()) { + if (bpByNameserviceId.containsKey(nameserviceId)) { + toRefresh.add(nameserviceId); + } else { + toAdd.add(nameserviceId); + } + } + + // Step 2. Any nameservices we currently have but are no longer present + // need to be removed. + // 计算当前DN需要删除的nameservice + toRemove = Sets.newHashSet(Sets.difference( + bpByNameserviceId.keySet(), addrMap.keySet())); + + // Step 3. 启动新的nameservice + if (!toAdd.isEmpty()) { + + for (String nsToAdd : toAdd) { + Map nnIdToAddr = addrMap.get(nsToAdd); + Map nnIdToLifelineAddr = + lifelineAddrMap.get(nsToAdd); + ArrayList addrs = + Lists.newArrayListWithCapacity(nnIdToAddr.size()); + ArrayList nnIds = + Lists.newArrayListWithCapacity(nnIdToAddr.size()); + ArrayList lifelineAddrs = + Lists.newArrayListWithCapacity(nnIdToAddr.size()); + for (String nnId : nnIdToAddr.keySet()) { + addrs.add(nnIdToAddr.get(nnId)); + nnIds.add(nnId); + lifelineAddrs.add(nnIdToLifelineAddr != null ? + nnIdToLifelineAddr.get(nnId) : null); + } + BPOfferService bpos = createBPOS(nsToAdd, nnIds, addrs, + lifelineAddrs); + bpByNameserviceId.put(nsToAdd, bpos); + offerServices.add(bpos); + } + } + startAll(); + } + + // Step 4. 停止掉老的nameservice. This happens outside + // of the synchronized(this) lock since they need to call + // back to .remove() from another thread + if (!toRemove.isEmpty()) { + + for (String nsToRemove : toRemove) { + BPOfferService bpos = bpByNameserviceId.get(nsToRemove); + bpos.stop(); + bpos.join(); + // they will call remove on their own + } + } + + // Step 5. Update nameservices whose NN list has changed + // 更新nameservices + if (!toRefresh.isEmpty()) { + + for (String nsToRefresh : toRefresh) { + BPOfferService bpos = bpByNameserviceId.get(nsToRefresh); + Map nnIdToAddr = addrMap.get(nsToRefresh); + Map nnIdToLifelineAddr = + lifelineAddrMap.get(nsToRefresh); + ArrayList addrs = + Lists.newArrayListWithCapacity(nnIdToAddr.size()); + ArrayList lifelineAddrs = + Lists.newArrayListWithCapacity(nnIdToAddr.size()); + ArrayList nnIds = Lists.newArrayListWithCapacity( + nnIdToAddr.size()); + for (String nnId : nnIdToAddr.keySet()) { + addrs.add(nnIdToAddr.get(nnId)); + lifelineAddrs.add(nnIdToLifelineAddr != null ? + nnIdToLifelineAddr.get(nnId) : null); + nnIds.add(nnId); + } + try { + UserGroupInformation.getLoginUser() + .doAs(new PrivilegedExceptionAction() { + @Override + public Object run() throws Exception { + // 刷新NNList 核心实现. + bpos.refreshNNList(nsToRefresh, nnIds, addrs, lifelineAddrs); + return null; + } + }); + } catch (InterruptedException ex) { + IOException ioe = new IOException(); + ioe.initCause(ex.getCause()); + throw ioe; + } + } + } +} +``` + +