4. SOFAJRaft源码分析— RheaKV初始化做了什么？

前言

由于RheaKV要讲起来篇幅比较长，所以这里分成几个章节来讲，这一章讲一讲RheaKV初始化做了什么？

我们先来给个例子，我们从例子来讲：

public static void main(final String[] args) throws Exception {
final PlacementDriverOptions pdOpts = PlacementDriverOptionsConfigured.newConfigured()
.withFake(true) // use a fake pd
.config();
final StoreEngineOptions storeOpts = StoreEngineOptionsConfigured.newConfigured() //
.withStorageType(StorageType.RocksDB)
.withRocksDBOptions(RocksDBOptionsConfigured.newConfigured().withDbPath(Configs.DB_PATH).config())
.withRaftDataPath(Configs.RAFT_DATA_PATH)
.withServerAddress(new Endpoint("127.0.0.1", 8181))
.config();

final RheaKVStoreOptions opts = RheaKVStoreOptionsConfigured.newConfigured() //
.withClusterName(Configs.CLUSTER_NAME) //
.withInitialServerList(Configs.ALL_NODE_ADDRESSES)
.withStoreEngineOptions(storeOpts) //
.withPlacementDriverOptions(pdOpts) //
.config();
System.out.println(opts);
final Node node = new Node(opts);
node.start();
Runtime.getRuntime().addShutdownHook(new Thread(node::stop));
System.out.println("server1 start OK");
}

这里为了简化逻辑，使用的无PD设置

Node的实现：

public class Node {

private final RheaKVStoreOptions options;

private RheaKVStore              rheaKVStore;

public Node(RheaKVStoreOptions options) {
this.options = options;
}

public void start() {
this.rheaKVStore = new DefaultRheaKVStore();
this.rheaKVStore.init(this.options);
}

public void stop() {
this.rheaKVStore.shutdown();
}

public RheaKVStore getRheaKVStore() {
return rheaKVStore;
}
}

所以这里是初始化一个DefaultRheaKVStore，并调用其init方法进行初始化

RheaKV 默认存储DefaultRheaKVStore

由于DefaultRheaKVStore的初始化方法都是在init方法中完成，所以这里直接看DefaultRheaKVStore的init方法。

public synchronized boolean init(final RheaKVStoreOptions opts) {
//1. 如果已经启动了，那么直接返回
if (this.started) {
LOG.info("[DefaultRheaKVStore] already started.");
return true;
}
this.opts = opts;
// init placement driver
// 2.根据PDoptions设置PD
final PlacementDriverOptions pdOpts = opts.getPlacementDriverOptions();
final String clusterName = opts.getClusterName();
Requires.requireNonNull(pdOpts, "opts.placementDriverOptions");
Requires.requireNonNull(clusterName, "opts.clusterName");
//设置集群
if (Strings.isBlank(pdOpts.getInitialServerList())) {
// if blank, extends parent's value
pdOpts.setInitialServerList(opts.getInitialServerList());
}
//如果是无 PD 场景， RheaKV 提供 Fake PD Client
if (pdOpts.isFake()) {
this.pdClient = new FakePlacementDriverClient(opts.getClusterId(), clusterName);
} else {
this.pdClient = new RemotePlacementDriverClient(opts.getClusterId(), clusterName);
}
//初始化PD
if (!this.pdClient.init(pdOpts)) {
LOG.error("Fail to init [PlacementDriverClient].");
return false;
}
// init store engine
//3. 初始化存储引擎
final StoreEngineOptions stOpts = opts.getStoreEngineOptions();
if (stOpts != null) {
stOpts.setInitialServerList(opts.getInitialServerList());
this.storeEngine = new StoreEngine(this.pdClient);
//初始化存储引擎
if (!this.storeEngine.init(stOpts)) {
LOG.error("Fail to init [StoreEngine].");
return false;
}
}
//获取当前节点的ip和端口号
final Endpoint selfEndpoint = this.storeEngine == null ? null : this.storeEngine.getSelfEndpoint();
final RpcOptions rpcOpts = opts.getRpcOptions();
Requires.requireNonNull(rpcOpts, "opts.rpcOptions");
//4. 初始化一个RpcService，并重写getLeader方法
this.rheaKVRpcService = new DefaultRheaKVRpcService(this.pdClient, selfEndpoint) {

@Override
public Endpoint getLeader(final long regionId, final boolean forceRefresh, final long timeoutMillis) {
final Endpoint leader = getLeaderByRegionEngine(regionId);
if (leader != null) {
return leader;
}
return super.getLeader(regionId, forceRefresh, timeoutMillis);
}
};
if (!this.rheaKVRpcService.init(rpcOpts)) {
LOG.error("Fail to init [RheaKVRpcService].");
return false;
}
//获取重试次数，默认重试两次
this.failoverRetries = opts.getFailoverRetries();
//默认5000
this.futureTimeoutMillis = opts.getFutureTimeoutMillis();
//是否只从leader读取数据，默认为true
this.onlyLeaderRead = opts.isOnlyLeaderRead();
//5.初始化kvDispatcher， 这里默认为true
if (opts.isUseParallelKVExecutor()) {
//获取当前cpu
final int numWorkers = Utils.cpus();
//向左移动4位，相当于乘以16
final int bufSize = numWorkers << 4;
final String name = "parallel-kv-executor";
final ThreadFactory threadFactory = Constants.THREAD_AFFINITY_ENABLED
//这里选择是否启用线程亲和性ThreadFactory
? new AffinityNamedThreadFactory(name, true) : new NamedThreadFactory(name, true);
//初始化Dispatcher
this.kvDispatcher = new TaskDispatcher(bufSize, numWorkers, WaitStrategyType.LITE_BLOCKING_WAIT,
threadFactory);
}
this.batchingOpts = opts.getBatchingOptions();
//默认是true
if (this.batchingOpts.isAllowBatching()) {
//这几个batching暂时不知道是用来做什么的，等用到再分析
this.getBatching = new GetBatching(KeyEvent::new, "get_batching",
new GetBatchingHandler("get", false));
this.getBatchingOnlySafe = new GetBatching(KeyEvent::new, "get_batching_only_safe",
new GetBatchingHandler("get_only_safe", true));
this.putBatching = new PutBatching(KVEvent::new, "put_batching",
new PutBatchingHandler("put"));
}
LOG.info("[DefaultRheaKVStore] start successfully, options: {}.", opts);
return this.started = true;
}

1. 校验是否启动，如果已经启动了，那么直接返回
2. 根据PDoptions设置PD，PD 是全局的中心总控节点，负责整个集群的调度管理，维护 RegionRouteTable 路由表。这里我们不启用 PD，所以实例化一个FakePlacementDriverClient，并初始化
3. 初始化存储引擎，目前 StoreEngine 存储引擎支持 MemoryDB 和 RocksDB 两种实现，我们这里用的是RocksDB，待会下面补充init方法讲解
4. 初始化一个rheaKVRpcService，针对 KV 存储服务的 RPC Client 客户端封装，实现 Failover 逻辑。并设置重试两次，等待超时时间futureTimeoutMillis是5000毫秒，默认只从leader读取数据
5. 初始化kvDispatcher

初始化存储引擎

初始化的操作时在StoreEngine的init方法里面实现的，我们直接看这个方法的实现，这个方法是初始化核心对象，逻辑较为复杂，希望有点耐心看完：

StoreEngine#init

public synchronized boolean init(final StoreEngineOptions opts) {
if (this.started) {
LOG.info("[StoreEngine] already started.");
return true;
}
this.storeOpts = Requires.requireNonNull(opts, "opts");
Endpoint serverAddress = Requires.requireNonNull(opts.getServerAddress(), "opts.serverAddress");
//获取ip和端口
final int port = serverAddress.getPort();
final String ip = serverAddress.getIp();
//如果传入的IP为空，那么就设置启动机器ip作为serverAddress的ip
if (ip == null || Utils.IP_ANY.equals(ip)) {
serverAddress = new Endpoint(NetUtil.getLocalCanonicalHostName(), port);
opts.setServerAddress(serverAddress);
}
//获取度量上报时间
final long metricsReportPeriod = opts.getMetricsReportPeriod();
// init region options
List<RegionEngineOptions> rOptsList = opts.getRegionEngineOptionsList();
//1. 如果RegionEngineOptions为空，则默认初始化一个
if (rOptsList == null || rOptsList.isEmpty()) {
// -1 region
final RegionEngineOptions rOpts = new RegionEngineOptions();
rOpts.setRegionId(Constants.DEFAULT_REGION_ID);
rOptsList = Lists.newArrayList();
rOptsList.add(rOpts);
opts.setRegionEngineOptionsList(rOptsList);
}
//获取集群名
final String clusterName = this.pdClient.getClusterName();
//2. 遍历rOptsList集合，为其中的RegionEngineOptions对象设置参数
for (final RegionEngineOptions rOpts : rOptsList) {
//用集群名+“-”+RegionId 拼接设置为RaftGroupId
rOpts.setRaftGroupId
3ff8
(JRaftHelper.getJRaftGroupId(clusterName, rOpts.getRegionId()));
rOpts.setServerAddress(serverAddress);
rOpts.setInitialServerList(opts.getInitialServerList());
if (rOpts.getNodeOptions() == null) {
// copy common node options
rOpts.setNodeOptions(opts.getCommonNodeOptions() == null ? new NodeOptions() : opts
.getCommonNodeOptions().copy());
}
//如果原本没有设置度量上报时间，那么就重置一下
if (rOpts.getMetricsReportPeriod() <= 0 && metricsReportPeriod > 0) {
// extends store opts 300
rOpts.setMetricsReportPeriod(metricsReportPeriod);
}
}
// init store
// 3. 初始化Store和Store里面的region
final Store store = this.pdClient.getStoreMetadata(opts);
if (store == null || store.getRegions() == null || store.getRegions().isEmpty()) {
LOG.error("Empty store metadata: {}.", store);
return false;
}
this.storeId = store.getId();
// init executors
//4. 初始化执行器
if (this.readIndexExecutor == null) {
this.readIndexExecutor = StoreEngineHelper.createReadIndexExecutor(opts.getReadIndexCoreThreads());
}
if (this.raftStateTrigger == null) {
this.raftStateTrigger = StoreEngineHelper.createRaftStateTrigger(opts.getLeaderStateTriggerCoreThreads());
}
if (this.snapshotExecutor == null) {
this.snapshotExecutor = StoreEngineHelper.createSnapshotExecutor(opts.getSnapshotCoreThreads());
}
// init rpc executors 默认false
final boolean useSharedRpcExecutor = opts.isUseSharedRpcExecutor();
//5. 初始化rpc远程执行器，用来执行RPCServer的Processors
if (!useSharedRpcExecutor) {
if (this.cliRpcExecutor == null) {
this.cliRpcExecutor = StoreEngineHelper.createCliRpcExecutor(opts.getCliRpcCoreThreads());
}
if (this.raftRpcExecutor == null) {
this.raftRpcExecutor = StoreEngineHelper.createRaftRpcExecutor(opts.getRaftRpcCoreThreads());
}
if (this.kvRpcExecutor == null) {
this.kvRpcExecutor = StoreEngineHelper.createKvRpcExecutor(opts.getKvRpcCoreThreads());
}
}
// init metrics
//做指标度量
startMetricReporters(metricsReportPeriod);
// init rpc server
//6. 初始化rpcServer，供其他服务调用
this.rpcServer = new RpcServer(port, true, true);
//为server加入各种processor
RaftRpcServerFactory.addRaftRequestProcessors(this.rpcServer, this.raftRpcExecutor, this.cliRpcExecutor);
StoreEngineHelper.addKvStoreRequestProcessor(this.rpcServer, this);
if (!this.rpcServer.start()) {
LOG.error("Fail to init [RpcServer].");
return false;
}
// init db store
//7. 根据不同的类型选择db
if (!initRawKVStore(opts)) {
return false;
}
// init all region engine
// 8. 为每个region初始化RegionEngine
if (!initAllRegionEngine(opts, store)) {
LOG.error("Fail to init all [RegionEngine].");
return false;
}
// heartbeat sender
//如果开启了自管理的集群，那么需要初始化心跳发送器
if (this.pdClient instanceof RemotePlacementDriverClient) {
HeartbeatOptions heartbeatOpts = opts.getHeartbeatOptions();
if (heartbeatOpts == null) {
heartbeatOpts = new HeartbeatOptions();
}
this.heartbeatSender = new HeartbeatSender(this);
if (!this.heartbeatSender.init(heartbeatOpts)) {
LOG.error("Fail to init [HeartbeatSender].");
return false;
}
}
this.startTime = System.currentTimeMillis();
LOG.info("[StoreEngine] start successfully: {}.", this);
return this.started = true;
}

我们从上面标了号的代码往下看：

1. 这里是校验StoreEngineOptions的regionEngineOptionsList是否为空，如果为空则默认初始化一个，然后加入到rOptsList集合里
2. 遍历rOptsList集合，并为其中的RegionEngineOptions对象设置集群信息
3. 实例化Store然后并根据RegionEngineOptions初始化里面的region
4. 初始化执行器
5. 初始化rpc远程执行器，用来执行RPCServer的Processors
6. 初始化rpcServer，供其他服务调用
7. 根据不同的类型选择db，目前 StoreEngine 存储引擎支持 MemoryDB 和 RocksDB 两种实现。MemoryDB基于 ConcurrentSkipListMap 实现。
8. 为每个region初始化RegionEngine

初始化Store和Store里面的region

这里会调用pdClient的getStoreMetadata方法进行初始化，这里我们看FakePlacementDriverClient的实现：
FakePlacementDriverClient#getStoreMetadata

public Store getStoreMetadata(final StoreEngineOptions opts) {
//实例化store
final Store store = new Store();
final List<RegionEngineOptions> rOptsList = opts.getRegionEngineOptionsList();
final List<Region> regionList = Lists.newArrayListWithCapacity(rOptsList.size());
store.setId(-1);
store.setEndpoint(opts.getServerAddress());
for (final RegionEngineOptions rOpts : rOptsList) {
//根据rOpts初始化Region实例加入到regionList中
regionList.add(getLocalRegionMetadata(rOpts));
}
store.setRegions(regionList);
return store;
}

这个方法里面会实例化一个store之后遍历rOptsList集合，在循环里面会根据rOptsList里面的RegionEngineOptions来调用getLocalRegionMetadata方法来实例化region，然后加入到regionList集合中。
在这里需要主要rOptsList列表和regionList列表的下标是一一对应的关系，在下面的代码中会用到这个对应关系。

在这里应该可以稍微理解到：

这张图的意义了，每个store下面会有很多的region。

然后我们再看看Region怎么被初始化的：
这里是调用FakePlacementDriverClient的父类AbstractPlacementDriverClient的getLocalRegionMetadata来进行初始化的
AbstractPlacementDriverClient#getLocalRegionMetadata

protected Region getLocalRegionMetadata(final RegionEngineOptions opts) {
final long regionId = Requires.requireNonNull(opts.getRegionId(), "opts.regionId");
Requires.requireTrue(regionId >= Region.MIN_ID_WITH_MANUAL_CONF, "opts.regionId must >= "
+ Region.MIN_ID_WITH_MANUAL_CONF);
Requires.requireTrue(regionId < Region.MAX_ID_WITH_MANUAL_CONF, "opts.regionId must < "
+ Region.MAX_ID_WITH_MANUAL_CONF);
final byte[] startKey = opts.getStartKeyBytes();
final byte[] endKey = opts.getEndKeyBytes();
final String initialServerList = opts.getInitialServerList();
//实例化region
final Region region = new Region();
final Configuration conf = new Configuration();
// region
region.setId(regionId);
region.setStartKey(startKey);
region.setEndKey(endKey);
region.setRegionEpoch(new RegionEpoch(-1, -1));
// peers
Requires.requireTrue(Strings.isNotBlank(initialServerList), "opts.initialServerList is blank");
//将集群ip和端口解析到peer中
conf.parse(initialServerList);
//每个region都会存有集群的信息
region.setPeers(JRaftHelper.toPeerList(conf.listPeers()));
this.regionRouteTable.addOrUpdateRegion(region);
return region;
}

Region 是最小的 KV 数据单元，可理解为一个数据分区或者分片，每个 Region 都有一个左闭右开的区间 [startKey, endKey)，这里初始化都是null，能够根据请求流量/负载/数据量大小等指标自动分裂以及自动副本搬迁。Region 有多个副本 Replication 构建 Raft Groups 存储在不同的 Store 节点，通过 Raft 协议日志复制功能数据同步到同 Group 的全部节点。

最后会将region存放到regionRouteTable中：

public void addOrUpdateRegion(final Region region) {
Requires.requireNonNull(region, "region");
Requires.requireNonNull(region.getRegionEpoch(), "regionEpoch");
final long regionId = region.getId();
final byte[] startKey = BytesUtil.nullToEmpty(region.getStartKey());
final StampedLock stampedLock = this.stampedLock;
final long stamp = stampedLock.writeLock();
try {
this.regionTable.put(regionId, region.copy());
this.rangeTable.put(startKey, regionId);
} finally {
stampedLock.unlockWrite(stamp);
}
}

在这个方法中将region根据regionId存入到regionTable中，然后根据startKey作为key存入到rangeTable中。

为每个region初始化RegionEngine

在initAllRegionEngine里面会初始化RegionEngine：
StoreEngine#initAllRegionEngine

private boolean initAllRegionEngine(final StoreEngineOptions opts, final Store store) {
Requires.requireNonNull(opts, "opts");
Requires.requireNonNull(store, "store");
//获取主目录
String baseRaftDataPath = opts.getRaftDataPath();
if (Strings.isNotBlank(baseRaftDataPath)) {
try {
FileUtils.forceMkdir(new File(baseRaftDataPath));
} catch (final Throwable t) {
LOG.error("Fail to make dir for raftDataPath: {}.", baseRaftDataPath);
return false;
}
} else {
baseRaftDataPath = "";
}
final Endpoint serverAddress = opts.getServerAddress();
final List<RegionEngineOptions> rOptsList = opts.getRegionEngineOptionsList();
final List<Region> regionList = store.getRegions();
//因为regionList是根据rOptsList来初始化的，所以这里校验一样数量是不是一样的
Requires.requireTrue(rOptsList.size() == regionList.size());
for (int i = 0; i < rOptsList.size(); i++) {
//一一对应的获取相应的RegionEngineOptions和region
final RegionEngineOptions rOpts = rOptsList.get(i);
final Region region = regionList.get(i);
//如果region路径是空的，那么就重新设值
if (Strings.isBlank(rOpts.getRaftDataPath())) {
final String childPath = "raft_data_region_" + region.getId() + "_" + serverAddress.getPort();
rOpts.setRaftDataPath(Paths.get(baseRaftDataPath, childPath).toString());
}
Requires.requireNonNull(region.getRegionEpoch(), "regionEpoch");
//根据Region初始化RegionEngine
final RegionEngine engine = new RegionEngine(region, this);
if (engine.init(rOpts)) {
//KV Server 服务端的请求处理服务
// 每个 RegionKVService 对应一个 Region，只处理本身 Region 范畴内的请求
final RegionKVService regionKVService = new DefaultRegionKVService(engine);
//放入到regionKVServiceTable中
registerRegionKVService(regionKVService);
//设置region与engine映射表
this.regionEngineTable.put(region.getId(), engine);
} else {
LOG.error("Fail to init [RegionEngine: {}].", region);
return false;
}
}
return true;
}

首先这个方法会初始化一个baseRaftDataPath作为主目录
然后将rOptsList和regionList都取出来，遍历rOptsList，并将RegionEngineOptions对应的region也找出来
然后这里会为每个region实例化一个RegionEngine，并将engine包装到RegionKVService中
最后将RegionKVService放入到regionKVServiceTable映射表中，将region放入到regionEngineTable映射表中

这里的RegionKVServic是KV Server 服务端的请求处理服务，一个 StoreEngine 中包含很多 RegionKVService, 每个 RegionKVService 对应一个 Region，只处理本身 Region 范畴内的请求。

初始化RegionEngine#init

public synchronized boolean init(final RegionEngineOptions opts) {
if (this.started) {
LOG.info("[RegionEngine: {}] already started.", this.region);
return true;
}
this.regionOpts = Requires.requireNonNull(opts, "opts");
//实例化状态机
this.fsm = new KVStoreStateMachine(this.region, this.storeEngine);

// node options
NodeOptions nodeOpts = opts.getNodeOptions();
if (nodeOpts == null) {
nodeOpts = new NodeOptions();
}
//如果度量间隔时间大于零，那么开启度量
final long metricsReportPeriod = opts.getMetricsReportPeriod();
if (metricsReportPeriod > 0) {
// metricsReportPeriod > 0 means enable metrics
nodeOpts.setEnableMetrics(true);
}
//初始化集群配置
nodeOpts.setInitialConf(new Configuration(JRaftHelper.toJRaftPeerIdList(this.region.getPeers())));
nodeOpts.setFsm(this.fsm);
//初始化各种日志的路径
final String raftDataPath = opts.getRaftDataPath();
try {
FileUtils.forceMkdir(new File(raftDataPath));
} catch (final Throwable t) {
LOG.error("Fail to make dir for raftDataPath {}.", raftDataPath);
return false;
}
if (Strings.isBlank(nodeOpts.getLogUri())) {
final Path logUri = Paths.get(raftDataPath, "log");
nodeOpts.setLogUri(logUri.toString());
}
if (Strings.isBlank(nodeOpts.getRaftMetaUri())) {
final Path meteUri = Paths.get(raftDataPath, "meta");
nodeOpts.setRaftMetaUri(meteUri.toString());
}
if (Strings.isBlank(nodeOpts.getSnapshotUri())) {
final Path snapshotUri = Paths.get(raftDataPath, "snapshot");
nodeOpts.setSnapshotUri(snapshotUri.toString());
}
LOG.info("[RegionEngine: {}], log uri: {}, raft meta uri: {}, snapshot uri: {}.", this.region,
nodeOpts.getLogUri(), nodeOpts.getRaftMetaUri(), nodeOpts.getSnapshotUri());
final Endpoint serverAddress = opts.getServerAddress();
final PeerId serverId = new PeerId(serverAddress, 0);
final RpcServer rpcServer = this.storeEngine.getRpcServer();
this.raftGroupService = new RaftGroupService(opts.getRaftGroupId(), serverId, nodeOpts, rpcServer, true);
//初始化node节点
this.node = this.raftGroupService.start(false);
RouteTable.getInstance().updateConfiguration(this.raftGroupService.getGroupId(), nodeOpts.getInitialConf());
if (this.node != null) {
final RawKVStore rawKVStore = this.storeEngine.getRawKVStore();
final Executor readIndexExecutor = this.storeEngine.getReadIndexExecutor();
//RaftRawKVStore 是 RheaKV 基于 Raft 复制状态机 KVStoreStateMachine 的 RawKVStore 接口 KV 存储实现
//RheaKV 的 Raft 入口，从这里开始 Raft 流程
this.raftRawKVStore = new RaftRawKVStore(this.node, rawKVStore, readIndexExecutor);
//拦截请求做指标度量
this.metricsRawKVStore = new MetricsRawKVStore(this.region.getId(), this.raftRawKVStore);
// metrics config
if (this.regionMetricsReporter == null && metricsReportPeriod > 0) {
final MetricRegistry metricRegistry = this.node.getNodeMetrics().getMetricRegistry();
if (metricRegistry != null) {
final ScheduledExecutorService scheduler = this.storeEngine.getMetricsScheduler();
// start raft node metrics reporter
this.regionMetricsReporter = Slf4jReporter.forRegistry(metricRegistry) //
.prefixedWith("region_" + this.region.getId()) //
.withLoggingLevel(Slf4jReporter.LoggingLevel.INFO) //
.outputTo(LOG) //
.scheduleOn(scheduler) //
.shutdownExecut
1bd9
orOnStop(scheduler != null) //
.build();
this.regionMetricsReporter.start(metricsReportPeriod, TimeUnit.SECONDS);
}
}
this.started = true;
LOG.info("[RegionEngine] start successfully: {}.", this);
}
return this.started;
}

走到了这里可以找得到我在第一讲的时候讲过熟悉的几个实例了。如果不熟悉的话，不妨去翻阅一下我的第一篇文章：1. SOFAJRaft源码分析— SOFAJRaft启动时做了什么？
在这里会实例化状态机，是KVStoreStateMachine的实例；
收动为LogUri、RaftMetaUri、SnapshotUri赋值，并获取storeEngine里的rpcServer；
启动raftGroupService返回经过初始化的node；
接下来会实例化raftRawKVStore，这个实例是RheaKV 的 Raft 入口，从这里开始 Raft 流程，所有的RheaKV数据都是通过它来处理。

总结

RheaKV初始化也是讲了很多的内容，这一篇讲了RheaKV在启动时需要初始化哪些组件，Store和Region又是一个怎样的关系，已经JRaft是在哪里启动的，状态机是在哪里设置的等等，内容也是非常的丰富。从这里也可以感受到，看到一个好的架构设计就是一种享受。