hdfs/dataNode启动过程.md

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+
+# 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<StorageLocation> dataDirs,
+    Configuration conf, SecureResources resources) throws IOException {
+  List<StorageLocation> 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<StorageLocation> 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<String, Map<String, InetSocketAddress>> addrMap,
+    Map<String, Map<String, InetSocketAddress>> lifelineAddrMap)
+    throws IOException {
+
+  Set<String> toRefresh = Sets.newLinkedHashSet();
+  Set<String> toAdd = Sets.newLinkedHashSet();
+  Set<String> 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<String, InetSocketAddress> nnIdToAddr = addrMap.get(nsToAdd);
+        Map<String, InetSocketAddress> nnIdToLifelineAddr =
+            lifelineAddrMap.get(nsToAdd);
+        ArrayList<InetSocketAddress> addrs =
+            Lists.newArrayListWithCapacity(nnIdToAddr.size());
+        ArrayList<String> nnIds =
+            Lists.newArrayListWithCapacity(nnIdToAddr.size());
+        ArrayList<InetSocketAddress> 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<String, InetSocketAddress> nnIdToAddr = addrMap.get(nsToRefresh);
+      Map<String, InetSocketAddress> nnIdToLifelineAddr =
+          lifelineAddrMap.get(nsToRefresh);
+      ArrayList<InetSocketAddress> addrs =
+          Lists.newArrayListWithCapacity(nnIdToAddr.size());
+      ArrayList<InetSocketAddress> lifelineAddrs =
+          Lists.newArrayListWithCapacity(nnIdToAddr.size());
+      ArrayList<String> 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<Object>() {
+              @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;
+      }
+    }
+  }
+}
+```
+
+