hdfs2.6.2源码学习：Day2-DataNode启动流程分析

DataNode启动流程分析

DataNode类源码学习

这个类代码比较多，就不全部浏览了，先把开头部分的参数以及构造器大致浏览一下，然后看main方法

这一句比较有意思：

* DataNodes spend their lives in an endless loop of asking

* the NameNode for something to do. A NameNode cannot connect

* to a DataNode directly; a NameNode simply returns values from

* functions invoked by a DataNode.

main方法

public static voidmain(String args[]) {

//判断参数是不是打印帮助信息，如果是，打印帮助信息并退出

if(DFSUtil.parseHelpArgument(args,DataNode.USAGE,System.out, true)) {

System.exit(0);

}

secureMain(args, null);

}

secureMain调用了createDataNode方法

public staticDataNodecreateDataNode(String args[],Configuration conf,

SecureResources resources) throwsIOException {

//创建datanode

DataNode dn = instantiateDataNode(args,conf,resources);

if(dn !=null) {

//启动datanode内部服务

dn.runDatanodeDaemon();

}

returndn;

}

instantiateDataNode方法

public staticDataNodeinstantiateDataNode(String args [],Configuration conf,

SecureResources resources) throwsIOException {

if(conf ==null)

conf =newHdfsConfiguration();

if(args !=null) {

// parse generic hadoop options

GenericOptionsParser hParser = newGenericOptionsParser(conf,args);

args = hParser.getRemainingArgs();

}

if(!parseArguments(args,conf)) {

printUsage(System.err);

return null;

}

//取得datanode的实际数据存放位置

Collection<StorageLocation> dataLocations = getStorageLocations(conf);

UserGroupInformation.setConfiguration(conf);

SecurityUtil.login(conf,DFS_DATANODE_KEYTAB_FILE_KEY,

DFS_DATANODE_KERBEROS_PRINCIPAL_KEY);

//创建实例

returnmakeInstance(dataLocations,conf,resources);

}

makeInstance方法

staticDataNodemakeInstance(Collection<StorageLocation> dataDirs,

Configuration conf,SecureResources resources)throwsIOException {

LocalFileSystem localFS = FileSystem.getLocal(conf);

//本地目录权限，默认是700

FsPermission permission = newFsPermission(

conf.get(DFS_DATANODE_DATA_DIR_PERMISSION_KEY,

DFS_DATANODE_DATA_DIR_PERMISSION_DEFAULT));

//用来创建本地目录和检查目录权限

DataNodeDiskChecker dataNodeDiskChecker =

newDataNodeDiskChecker(permission);

//返回经过检查后没问题的目录（检查过程中可能会创建该目录）

List<StorageLocation> locations =

checkStorageLocations(dataDirs,localFS,dataNodeDiskChecker);

DefaultMetricsSystem.initialize("DataNode");

assertlocations.size() >0:"number of data directories should be > 0";

//创建dataNode对象

return new DataNode(conf,locations,resources);

}

DataNode构造方法

DataNode(finalConfiguration conf,

finalList<StorageLocation> dataDirs,

finalSecureResources resources)throwsIOException {

super(conf);

this.lastDiskErrorCheck=0;

this.maxNumberOfBlocksToLog= conf.getLong(DFS_MAX_NUM_BLOCKS_TO_LOG_KEY,

DFS_MAX_NUM_BLOCKS_TO_LOG_DEFAULT);

//配置各种参数

this.usersWithLocalPathAccess= Arrays.asList(

conf.getTrimmedStrings(DFSConfigKeys.DFS_BLOCK_LOCAL_PATH_ACCESS_USER_KEY));

this.connectToDnViaHostname= conf.getBoolean(

DFSConfigKeys.DFS_DATANODE_USE_DN_HOSTNAME,

DFSConfigKeys.DFS_DATANODE_USE_DN_HOSTNAME_DEFAULT);

this.getHdfsBlockLocationsEnabled= conf.getBoolean(

DFSConfigKeys.DFS_HDFS_BLOCKS_METADATA_ENABLED,

DFSConfigKeys.DFS_HDFS_BLOCKS_METADATA_ENABLED_DEFAULT);

this.supergroup= conf.get(DFSConfigKeys.DFS_PERMISSIONS_SUPERUSERGROUP_KEY,

DFSConfigKeys.DFS_PERMISSIONS_SUPERUSERGROUP_DEFAULT);

//是否启用权限

this.isPermissionEnabled= conf.getBoolean(

DFSConfigKeys.DFS_PERMISSIONS_ENABLED_KEY,

DFSConfigKeys.DFS_PERMISSIONS_ENABLED_DEFAULT);

confVersion="core-"+

conf.get("hadoop.common.configuration.version","UNSPECIFIED") +

",hdfs-"+

conf.get("hadoop.hdfs.configuration.version","UNSPECIFIED");

// Determine whether we should try to pass file descriptors to clients.

if(conf.getBoolean(DFSConfigKeys.DFS_CLIENT_READ_SHORTCIRCUIT_KEY,

DFSConfigKeys.DFS_CLIENT_READ_SHORTCIRCUIT_DEFAULT)) {

String reason = DomainSocket.getLoadingFailureReason();

if(reason !=null) {

LOG.warn("File descriptor passing is disabled because " + reason);

this.fileDescriptorPassingDisabledReason= reason;

}else{

LOG.info("File descriptor passing is enabled.");

this.fileDescriptorPassingDisabledReason=null;

}

}else{

this.fileDescriptorPassingDisabledReason=

"File descriptor passing was not configured.";

LOG.debug(this.fileDescriptorPassingDisabledReason);

}

try{

//取hostname，优先从dfs.datanode.hostname配置取

hostName=getHostName(conf);

LOG.info("Configured hostname is " +hostName);

//启动datanode

startDataNode(conf,dataDirs,resources);

}catch(IOException ie) {

shutdown();

throwie;

}

}

startDataNode方法

voidstartDataNode(Configuration conf,

List<StorageLocation> dataDirs,

SecureResources resources

)throwsIOException {

// settings global for all BPs in the Data Node

this.secureResources= resources;

synchronized(this) {

this.dataDirs= dataDirs;

}

this.conf= conf;

this.dnConf=newDNConf(conf);

checkSecureConfig(dnConf,conf,resources);

//这个不太明白是干什么的？

this.spanReceiverHost= SpanReceiverHost.getInstance(conf);

if(dnConf.maxLockedMemory>0) {

if(!NativeIO.POSIX.getCacheManipulator().verifyCanMlock()) {

throw newRuntimeException(String.format(

"Cannot start datanode because the configured max locked memory" +

" size (%s) is greater than zero and native code is not available.",

DFS_DATANODE_MAX_LOCKED_MEMORY_KEY));

}

if(Path.WINDOWS) {

NativeIO.Windows.extendWorkingSetSize(dnConf.maxLockedMemory);

}else{

longulimit = NativeIO.POSIX.getCacheManipulator().getMemlockLimit();

if(dnConf.maxLockedMemory> ulimit) {

throw newRuntimeException(String.format(

"Cannot start datanode because the configured max locked memory" +

" size (%s) of %d bytes is more than the datanode's available" +

" RLIMIT_MEMLOCK ulimit of %d bytes.",

DFS_DATANODE_MAX_LOCKED_MEMORY_KEY,

dnConf.maxLockedMemory,

ulimit));

}

}

}

LOG.info("Starting DataNode with maxLockedMemory = " +

dnConf.maxLockedMemory);

//存储数据相关的类，规定了一些存储本地文件时的格式，比如以subdir开头的文件夹、以blk_开头的块文件等

storage=newDataStorage();

// global DN settings

registerMXBean();

//创建块文件接收器服务

initDataXceiver(conf);

//启动web页面，默认端口是50075

startInfoServer(conf);

//启动一个java监控线程，监控java虚拟机（因为垃圾回收等）暂停的次数，

//内部实现是一个线程每隔一段时间就休眠一下，如果休眠时间明显比规定时间长，则判断jvm暂停过

pauseMonitor=newJvmPauseMonitor(conf);

pauseMonitor.start();

//为每个block pool管理一个BlockTokenSecretManager

// BlockPoolTokenSecretManager is required to create ipc server.

this.blockPoolTokenSecretManager=newBlockPoolTokenSecretManager();

// Login is done by now. Set the DN user name.

dnUserName= UserGroupInformation.getCurrentUser().getShortUserName();

LOG.info("dnUserName = " +dnUserName);

LOG.info("supergroup = " +supergroup);

//初始化ipc服务（用于通信）

initIpcServer(conf);

//监控数据

metrics= DataNodeMetrics.create(conf,getDisplayName());

metrics.getJvmMetrics().setPauseMonitor(pauseMonitor);

//管理BPOfferService相关

blockPoolManager=newBlockPoolManager(this);

//这里向namenode注册了自己，并开始轮询namenode请求待执行命令？

blockPoolManager.refreshNamenodes(conf);

// Create the ReadaheadPool from the DataNode context so we can

// exit without having to explicitly shutdown its thread pool.

readaheadPool= ReadaheadPool.getInstance();

saslClient=newSaslDataTransferClient(dnConf.conf,

dnConf.saslPropsResolver,dnConf.trustedChannelResolver);

saslServer=newSaslDataTransferServer(dnConf,blockPoolTokenSecretManager);

}

创建完DataNode后，调用runDatanodeDaemon方法

public voidrunDatanodeDaemon()throwsIOException {

// blockPoolManager服务启动,并开始轮询namenode请求待执行命令？

blockPoolManager.startAll();

//数据传输服务启动

// start dataXceiveServer

dataXceiverServer.start();

if(localDataXceiverServer!=null) {

localDataXceiverServer.start();

}

// ipc服务启动

ipcServer.start();

//插件启动

startPlugins(conf);

}