前言

在之前的系列中,我们讲解了关于Seata基本介绍和实际应用,今天带来的这篇,就给大家分析一下Seata的源码是如何一步一步实现的。读源码的时候我们需要俯瞰起全貌,不要去扣一个一个的细节,这样我们学习起来会快捷而且有效率,我们学习源码需要掌握的是整体思路和核心点。

首先 Seata 客户端启动一般分为以下几个流程:

  1. 自动加载Bean属性和配置信息
  2. 初始化TM
  3. 初始化RM
  4. 初始化分布式事务客户端完成,完成代理数据库配置
  5. 连接TC(Seata服务端),注册RM和TM
  6. 开启全局事务

在这篇源码的讲解中,我们主要以AT模式为主导,官网也是主推AT模式,我们在上篇的文章中也讲解过,感兴趣的小伙伴可以去看一看分布式事务(Seata) 四大模式详解,在官网中也提供了对应的流程地址:https://seata.io/zh-cn/docs/dev/mode/at-mode.html ,在这里我们只是做一些简单的介绍,AT模式主要分为两个阶段:

一阶段:

  • 解析SQL,获取SQL类型(CRUD)、表信息、条件(where) 等相关信息
  • 查询前镜像(改变之前的数据),根据解析得到的条件信息,生成查询语句,定位数据
  • 执行业务SQL,更新数据
  • 查询后镜像(改变后的数据),根据前镜像的结果,通过主键都给你为数据
  • 插入回滚日志,将前后镜像数据以及业务SQL等信息,组织成一条回滚日志记录,插入到undo Log表中
  • 提交前,向TC注册分支,申请全局锁
  • 本地事务提交,业务数据的更细腻和生成的undoLog一起提交
  • 将本地事务提交的结果通知给TC

二阶段:

如果TC收到的是回滚请求

  • 开启本地事务,通过XID和BranchID查找到对应的undo Log记录
  • 根据undoLog中的前镜像和业务SQL的相关信息生成并执行回滚语句
  • 提交本地事务,将本地事务的执行结果(分支事务回滚的信息)通知给TC

如果没问题,执行提交操作

  • 收到TC分支提交请求,将请求放入到一个异步任务的队列中,马上返回提交成功的结果给TC
  • 异步任务阶段的分支提交请求删除undoLog中记录

源码入口

接下来,我们就需要从官网中去下载源码,下载地址:https://seata.io/zh-cn/blog/download.html,选择 source 即可,下载完成之后,通过IDEA打开项目。

源码下载下来之后,我们应该如何去找入口呢?首先我们需要找到对应引入的 Seataspring-alibaba-seata,我们在回想一下,我们开启事务的时候,是不是添加过一个@GlobalTransactional的注解,这个注解就是我们入手的一个点,我们在 spring.factories 中看到有一个 GlobalTransactionAutoConfiguration,这个就是我们需要关注的点,也就是我们源码的入口

GlobalTransactionAutoConfiguration 中我们找到一个用Bean注入的方法 globalTransactionScanner ,这个就是全局事务扫描器,这个类型主要负责加载配置,注入相关的Bean

这里给大家展示了当前GlobalTransactionScanner的类关系图,其中我们现在继承了Aop的AbstractAutoProxyCreator类型,在这其中有一个重点方法,这个方法就是判断Bean对象是否需要代理,是否需要增强。

@Configuration@EnableConfigurationProperties(SeataProperties.class)public class GlobalTransactionAutoConfiguration {//全局事务扫描器@Beanpublic GlobalTransactionScanner globalTransactionScanner() {String applicationName = applicationContext.getEnvironment().getProperty("spring.application.name");String txServiceGroup = seataProperties.getTxServiceGroup();if (StringUtils.isEmpty(txServiceGroup)) {txServiceGroup = applicationName + "-fescar-service-group";seataProperties.setTxServiceGroup(txServiceGroup);}// 构建全局扫描器,传入参数:应用名、事务分组名,失败处理器return new GlobalTransactionScanner(applicationName, txServiceGroup);}}

在这其中我们要关心的是 GlobalTransactionScanner 这个类型,这个类型扫描 @GlobalTransactional 注解,并对代理方法进行拦截增强事务的功能。我们就从源码中搜索这个GlobalTransactionScanner类,看看里面具体是做了什么

/** * The type Global transaction scanner. * 全局事务扫描器 * @author slievrly */public class GlobalTransactionScanner//AbstractAutoProxyCreator AOP动态代理 增强Beanextends AbstractAutoProxyCreator/** * ConfigurationChangeListener: 监听器基准接口 * InitializingBean: Bean初始化 * ApplicationContextAware: Spring容器 * DisposableBean: Spring 容器销毁 */implements ConfigurationChangeListener, InitializingBean, ApplicationContextAware, DisposableBean {private final String applicationId;//服务名private final String txServiceGroup;//事务分组private void initClient() {//启动日志if (LOGGER.isInfoEnabled()) {LOGGER.info("Initializing Global Transaction Clients ... ");}//检查应用名以及事务分组名,为空抛出异常IllegalArgumentExceptionif (DEFAULT_TX_GROUP_OLD.equals(txServiceGroup)) {LOGGER.warn("the default value of seata.tx-service-group: {} has already changed to {} since Seata 1.5, " +"please change your default configuration as soon as possible " +"and we don't recommend you to use default tx-service-group's value provided by seata",DEFAULT_TX_GROUP_OLD, DEFAULT_TX_GROUP);}if (StringUtils.isNullOrEmpty(applicationId) || StringUtils.isNullOrEmpty(txServiceGroup)) {throw new IllegalArgumentException(String.format("applicationId: %s, txServiceGroup: %s", applicationId, txServiceGroup));}//init TM//初始化TMTMClient.init(applicationId, txServiceGroup, accessKey, secretKey);if (LOGGER.isInfoEnabled()) {LOGGER.info("Transaction Manager Client is initialized. applicationId[{}] txServiceGroup[{}]", applicationId, txServiceGroup);}//init RM//初始化RMRMClient.init(applicationId, txServiceGroup);if (LOGGER.isInfoEnabled()) {LOGGER.info("Resource Manager is initialized. applicationId[{}] txServiceGroup[{}]", applicationId, txServiceGroup);}if (LOGGER.isInfoEnabled()) {LOGGER.info("Global Transaction Clients are initialized. ");}registerSpringShutdownHook();}@Overridepublic void afterPropertiesSet() {if (disableGlobalTransaction) {if (LOGGER.isInfoEnabled()) {LOGGER.info("Global transaction is disabled.");}ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,(ConfigurationChangeListener)this);return;}if (initialized.compareAndSet(false, true)) {initClient();}} private void initClient() {//启动日志if (LOGGER.isInfoEnabled()) {LOGGER.info("Initializing Global Transaction Clients ... ");}//检查应用名以及事务分组名,为空抛出异常IllegalArgumentExceptionif (DEFAULT_TX_GROUP_OLD.equals(txServiceGroup)) {LOGGER.warn("the default value of seata.tx-service-group: {} has already changed to {} since Seata 1.5, " +"please change your default configuration as soon as possible " +"and we don't recommend you to use default tx-service-group's value provided by seata",DEFAULT_TX_GROUP_OLD, DEFAULT_TX_GROUP);}//检查应用名以及事务分组名,为空抛出异常IllegalArgumentExceptionif (StringUtils.isNullOrEmpty(applicationId) || StringUtils.isNullOrEmpty(txServiceGroup)) {throw new IllegalArgumentException(String.format("applicationId: %s, txServiceGroup: %s", applicationId, txServiceGroup));}//init TM//初始化TMTMClient.init(applicationId, txServiceGroup, accessKey, secretKey);if (LOGGER.isInfoEnabled()) {LOGGER.info("Transaction Manager Client is initialized. applicationId[{}] txServiceGroup[{}]", applicationId, txServiceGroup);}//init RM//初始化RMRMClient.init(applicationId, txServiceGroup);if (LOGGER.isInfoEnabled()) {LOGGER.info("Resource Manager is initialized. applicationId[{}] txServiceGroup[{}]", applicationId, txServiceGroup);}if (LOGGER.isInfoEnabled()) {LOGGER.info("Global Transaction Clients are initialized. ");}registerSpringShutdownHook();}//代理增强,Spring 所有的Bean都会经过这个方法@Overrideprotected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {// do checkers//检查bean和beanNameif (!doCheckers(bean, beanName)) {return bean;}try {//加锁防止并发synchronized (PROXYED_SET) {if (PROXYED_SET.contains(beanName)) {return bean;}interceptor = null;//check TCC proxy//检查是否为TCC模式if (TCCBeanParserUtils.isTccAutoProxy(bean, beanName, applicationContext)) {// init tcc fence clean task if enable useTccFence//如果启用useTccFence 失败 ,则初始化TCC清理任务TCCBeanParserUtils.initTccFenceCleanTask(TCCBeanParserUtils.getRemotingDesc(beanName), applicationContext);//TCC interceptor, proxy bean of sofa:reference/dubbo:reference, and LocalTCC//如果是,添加TCC拦截器interceptor = new TccActionInterceptor(TCCBeanParserUtils.getRemotingDesc(beanName));ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,(ConfigurationChangeListener)interceptor);} else {//不是TCCClass<?> serviceInterface = SpringProxyUtils.findTargetClass(bean);Class<?>[] interfacesIfJdk = SpringProxyUtils.findInterfaces(bean);//判断是否有相关事务注解,如果没有不进行代理if (!existsAnnotation(new Class[]{serviceInterface})&& !existsAnnotation(interfacesIfJdk)) {return bean;}//发现存在全局事务注解标注的Bean对象,添加拦截器if (globalTransactionalInterceptor == null) {//添加拦截器globalTransactionalInterceptor = new GlobalTransactionalInterceptor(failureHandlerHook);ConfigurationCache.addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,(ConfigurationChangeListener)globalTransactionalInterceptor);}interceptor = globalTransactionalInterceptor;}LOGGER.info("Bean[{}] with name [{}] would use interceptor [{}]", bean.getClass().getName(), beanName, interceptor.getClass().getName());//检查是否为代理对象if (!AopUtils.isAopProxy(bean)) {//不是代理对象,调用父级bean = super.wrapIfNecessary(bean, beanName, cacheKey);} else {//是代理对象,反射获取代理类中已经存在的拦截器组合,然后添加到这个集合中AdvisedSupport advised = SpringProxyUtils.getAdvisedSupport(bean);Advisor[] advisor = buildAdvisors(beanName, getAdvicesAndAdvisorsForBean(null, null, null));int pos;for (Advisor avr : advisor) {// Find the position based on the advisor's order, and add to advisors by pospos = findAddSeataAdvisorPosition(advised, avr);advised.addAdvisor(pos, avr);}}PROXYED_SET.add(beanName);return bean;}} catch (Exception exx) {throw new RuntimeException(exx);}}}

InitializingBean:中实现了一个 afterPropertiesSet()方法,在这个方法中,调用了initClient()

AbstractAutoProxyCreator:APO动态代理,在之前的的Nacos和Sentiel中都有这个代理类,AOP在我们越往深入学习,在学习源码的会见到的越来越多,越来越重要,很多相关代理,都是通过AOP进行增强,在这个类中,我们需要关注有一个wrapIfNecessary()方法, 这个方法主要是判断被代理的bean或者类是否需要代理增强,在这个方法中会调用GlobalTransactionalInterceptor.invoke()进行带来增强。

具体代码如下:

public class GlobalTransactionalInterceptor implements ConfigurationChangeListener, MethodInterceptor, SeataInterceptor {public GlobalTransactionalInterceptor(FailureHandler failureHandler) {this.failureHandler = failureHandler == null ? DEFAULT_FAIL_HANDLER : failureHandler;this.disable = ConfigurationFactory.getInstance().getBoolean(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION,DEFAULT_DISABLE_GLOBAL_TRANSACTION);this.order =ConfigurationFactory.getInstance().getInt(ConfigurationKeys.TM_INTERCEPTOR_ORDER, TM_INTERCEPTOR_ORDER);degradeCheck = ConfigurationFactory.getInstance().getBoolean(ConfigurationKeys.CLIENT_DEGRADE_CHECK,DEFAULT_TM_DEGRADE_CHECK);if (degradeCheck) {ConfigurationCache.addConfigListener(ConfigurationKeys.CLIENT_DEGRADE_CHECK, this);degradeCheckPeriod = ConfigurationFactory.getInstance().getInt(ConfigurationKeys.CLIENT_DEGRADE_CHECK_PERIOD, DEFAULT_TM_DEGRADE_CHECK_PERIOD);degradeCheckAllowTimes = ConfigurationFactory.getInstance().getInt(ConfigurationKeys.CLIENT_DEGRADE_CHECK_ALLOW_TIMES, DEFAULT_TM_DEGRADE_CHECK_ALLOW_TIMES);EVENT_BUS.register(this);if (degradeCheckPeriod > 0 && degradeCheckAllowTimes > 0) {startDegradeCheck();}}this.initDefaultGlobalTransactionTimeout();}@Overridepublic Object invoke(final MethodInvocation methodInvocation) throws Throwable {//获取执行的方法Class<?> targetClass =methodInvocation.getThis() != null ? AopUtils.getTargetClass(methodInvocation.getThis()) : null;Method specificMethod = ClassUtils.getMostSpecificMethod(methodInvocation.getMethod(), targetClass);if (specificMethod != null && !specificMethod.getDeclaringClass().equals(Object.class)) {final Method method = BridgeMethodResolver.findBridgedMethod(specificMethod);//获取GlobalTransactional(全局事务)、GlobalLock(全局锁)元数据final GlobalTransactional globalTransactionalAnnotation =getAnnotation(method, targetClass, GlobalTransactional.class);//GlobalLock会将本地事务的执行纳入Seata分布式事务的管理,共同竞争全局锁//保证全局事务在执行的时候,本地事务不可以操作全局事务的记录final GlobalLock globalLockAnnotation = getAnnotation(method, targetClass, GlobalLock.class);//获取全局锁boolean localDisable = disable || (degradeCheck && degradeNum >= degradeCheckAllowTimes);if (!localDisable) {if (globalTransactionalAnnotation != null || this.aspectTransactional != null) {AspectTransactional transactional;if (globalTransactionalAnnotation != null) {transactional = new AspectTransactional(globalTransactionalAnnotation.timeoutMills(),globalTransactionalAnnotation.name(), globalTransactionalAnnotation.rollbackFor(),globalTransactionalAnnotation.noRollbackForClassName(),globalTransactionalAnnotation.noRollbackFor(),globalTransactionalAnnotation.noRollbackForClassName(),globalTransactionalAnnotation.propagation(),globalTransactionalAnnotation.lockRetryInterval(),globalTransactionalAnnotation.lockRetryTimes());} else {transactional = this.aspectTransactional;}//执行全局事务return handleGlobalTransaction(methodInvocation, transactional);} else if (globalLockAnnotation != null) {//执行全局锁return handleGlobalLock(methodInvocation, globalLockAnnotation);}}}return methodInvocation.proceed();}}

具体流程图如下所示:

核心源码

在上面我们讲解到 GlobalTransactionalInterceptor 作为全局事务拦截器,一旦执行拦截,就会进入invoke方法,其中,我们会做 @GlobalTransactional 注解的判断,如果有这个注解的存在,会执行全局事务和全局锁,再执行全局事务的时候会调用 handleGlobalTransaction 全局事务处理器,获取事务信息,那我们接下来就来看一下 GlobalTransactionalInterceptor.handleGlobalTransaction 到底是如何执行全局事务的

Object handleGlobalTransaction(final MethodInvocation methodInvocation,final AspectTransactional aspectTransactional) throws Throwable {boolean succeed = true;try {return transactionalTemplate.execute(new TransactionalExecutor() {@Overridepublic Object execute() throws Throwable {return methodInvocation.proceed();}//获取事务名称,默认获取方法名public String name() {String name = aspectTransactional.getName();if (!StringUtils.isNullOrEmpty(name)) {return name;}return formatMethod(methodInvocation.getMethod());}/** * 解析GlobalTransation注解属性,封装对对象 * @return */@Overridepublic TransactionInfo getTransactionInfo() {// reset the value of timeout//获取超时时间,默认60秒int timeout = aspectTransactional.getTimeoutMills();if (timeout <= 0 || timeout == DEFAULT_GLOBAL_TRANSACTION_TIMEOUT) {timeout = defaultGlobalTransactionTimeout;}//构建事务信息对象TransactionInfo transactionInfo = new TransactionInfo();transactionInfo.setTimeOut(timeout);//超时时间transactionInfo.setName(name());//事务名称transactionInfo.setPropagation(aspectTransactional.getPropagation());//事务传播transactionInfo.setLockRetryInterval(aspectTransactional.getLockRetryInterval());//校验或占用全局锁重试间隔transactionInfo.setLockRetryTimes(aspectTransactional.getLockRetryTimes());//校验或占用全局锁重试次数Set<RollbackRule> rollbackRules = new LinkedHashSet<>();//其他构建信息for (Class<?> rbRule : aspectTransactional.getRollbackFor()) {rollbackRules.add(new RollbackRule(rbRule));}for (String rbRule : aspectTransactional.getRollbackForClassName()) {rollbackRules.add(new RollbackRule(rbRule));}for (Class<?> rbRule : aspectTransactional.getNoRollbackFor()) {rollbackRules.add(new NoRollbackRule(rbRule));}for (String rbRule : aspectTransactional.getNoRollbackForClassName()) {rollbackRules.add(new NoRollbackRule(rbRule));}transactionInfo.setRollbackRules(rollbackRules);return transactionInfo;}});} catch (TransactionalExecutor.ExecutionException e) {//执行异常TransactionalExecutor.Code code = e.getCode();switch (code) {case RollbackDone:throw e.getOriginalException();case BeginFailure:succeed = false;failureHandler.onBeginFailure(e.getTransaction(), e.getCause());throw e.getCause();case CommitFailure:succeed = false;failureHandler.onCommitFailure(e.getTransaction(), e.getCause());throw e.getCause();case RollbackFailure:failureHandler.onRollbackFailure(e.getTransaction(), e.getOriginalException());throw e.getOriginalException();case RollbackRetrying:failureHandler.onRollbackRetrying(e.getTransaction(), e.getOriginalException());throw e.getOriginalException();default:throw new ShouldNeverHappenException(String.format("Unknown TransactionalExecutor.Code: %s", code));}} finally {if (degradeCheck) {EVENT_BUS.post(new DegradeCheckEvent(succeed));}}}

在这里我们,主要关注一个重点方法 execute() ,这个方法主要用来执行事务的具体流程:

  • 获取事务信息
  • 执行全局事务
  • 发生异常全局回滚,各个数据通过UndoLog进行事务补偿
  • 全局事务提交
  • 清除所有资源

这个位置也是一个非常核心的一个位置,因为我们所有的业务进来以后都会去走这个位置,具体源码如下所示:

public Object execute(TransactionalExecutor business) throws Throwable {// 1. Get transactionInfo//获取事务信息TransactionInfo txInfo = business.getTransactionInfo();if (txInfo == null) {throw new ShouldNeverHappenException("transactionInfo does not exist");}// 1.1 Get current transaction, if not null, the tx role is 'GlobalTransactionRole.Participant'.//获取当前事务,主要获取XIDGlobalTransaction tx = GlobalTransactionContext.getCurrent();// 1.2 Handle the transaction propagation.//根据配置的不同事务传播行为,执行不同的逻辑Propagation propagation = txInfo.getPropagation();SuspendedResourcesHolder suspendedResourcesHolder = null;try {switch (propagation) {case NOT_SUPPORTED:// If transaction is existing, suspend it.if (existingTransaction(tx)) {suspendedResourcesHolder = tx.suspend();}// Execute without transaction and return.return business.execute();case REQUIRES_NEW:// If transaction is existing, suspend it, and then begin new transaction.if (existingTransaction(tx)) {suspendedResourcesHolder = tx.suspend();tx = GlobalTransactionContext.createNew();}// Continue and execute with new transactionbreak;case SUPPORTS:// If transaction is not existing, execute without transaction.if (notExistingTransaction(tx)) {return business.execute();}// Continue and execute with new transactionbreak;case REQUIRED:// If current transaction is existing, execute with current transaction,// else continue and execute with new transaction.break;case NEVER:// If transaction is existing, throw exception.if (existingTransaction(tx)) {throw new TransactionException(String.format("Existing transaction found for transaction marked with propagation 'never', xid = %s", tx.getXid()));} else {// Execute without transaction and return.return business.execute();}case MANDATORY:// If transaction is not existing, throw exception.if (notExistingTransaction(tx)) {throw new TransactionException("No existing transaction found for transaction marked with propagation 'mandatory'");}// Continue and execute with current transaction.break;default:throw new TransactionException("Not Supported Propagation:" + propagation);}// 1.3 If null, create new transaction with role 'GlobalTransactionRole.Launcher'.//如果当前事务为空,创建一个新的事务if (tx == null) {tx = GlobalTransactionContext.createNew();}// set current tx config to holderGlobalLockConfig previousConfig = replaceGlobalLockConfig(txInfo);try {// 2. If the tx role is 'GlobalTransactionRole.Launcher', send the request of beginTransaction to TC,//else do nothing. Of course, the hooks will still be triggered.//开始执行全局事务beginTransaction(txInfo, tx);Object rs;try {// Do Your Business// 执行当前业务逻辑//1、在TC注册当前分支事务,TC会在branch_table中插入一条分支事务数据//2、执行本地update语句,并在执行前后查询数据状态,并把数据前后镜像存入到undo_log中//3、远程调用其他应用,远程应用接收到XID,也会注册分支事务,写入branch_table以及本地undo_log表//4、会在lock_table表中插入全局锁数据(一个分支一条)rs = business.execute();} catch (Throwable ex) {// 3. The needed business exception to rollback.//发生异常全局回滚,每个事务通过undo_log表进行事务补偿completeTransactionAfterThrowing(txInfo, tx, ex);throw ex;}// 4. everything is fine, commit.//全局提交commitTransaction(tx);return rs;} finally {//5. clear//清理所有资源resumeGlobalLockConfig(previousConfig);triggerAfterCompletion();cleanUp();}} finally {// If the transaction is suspended, resume it.if (suspendedResourcesHolder != null) {tx.resume(suspendedResourcesHolder);}}}

这其中的第三步和第四步其实在向 TC(Seata-Server)发起全局事务的提交或者回滚,在这里我们首先关注执行全局事务的 beginTransaction() 方法

// 向TC发起请求,采用模板模式private void beginTransaction(TransactionInfo txInfo, GlobalTransaction tx) throws TransactionalExecutor.ExecutionException {try {triggerBeforeBegin();//对TC发起请求tx.begin(txInfo.getTimeOut(), txInfo.getName());triggerAfterBegin();} catch (TransactionException txe) {throw new TransactionalExecutor.ExecutionException(tx, txe,TransactionalExecutor.Code.BeginFailure);}}

在来关注其中,向TC发起请求的 tx.begin() 方法,而调用begin()方法的类为:DefaultGlobalTransaction

 @Overridepublic void begin(int timeout, String name) throws TransactionException {//判断调用者是否为TMif (role != GlobalTransactionRole.Launcher) {assertXIDNotNull();if (LOGGER.isDebugEnabled()) {LOGGER.debug("Ignore Begin(): just involved in global transaction [{}]", xid);}return;}assertXIDNull();String currentXid = RootContext.getXID();if (currentXid != null) {throw new IllegalStateException("Global transaction already exists," +" can't begin a new global transaction, currentXid = " + currentXid);}//获取XIDxid = transactionManager.begin(null, null, name, timeout);status = GlobalStatus.Begin;//绑定XIDRootContext.bind(xid);if (LOGGER.isInfoEnabled()) {LOGGER.info("Begin new global transaction [{}]", xid);}}

再来看一下 transactionManager.begin() 方法,这个时候使用的是 DefaultTransactionManager.begin 默认的事务管理者,来获取XID,传入事务相关的信息 ,***TC返回对应的全局事务XID,它调用的是DefaultTransactionManager.begin()方法

public String begin(String applicationId, String transactionServiceGroup, String name, int timeout)throws TransactionException {GlobalBeginRequest request = new GlobalBeginRequest();request.setTransactionName(name);request.setTimeout(timeout);//发送请求得到响应GlobalBeginResponse response = (GlobalBeginResponse) syncCall(request);if (response.getResultCode() == ResultCode.Failed) {throw new TmTransactionException(TransactionExceptionCode.BeginFailed, response.getMsg());}//返回XIDreturn response.getXid();}

在这里我们需要关注一个syncCall,在这里采用的是Netty通讯方式

private AbstractTransactionResponse syncCall(AbstractTransactionRequest request) throws TransactionException {try {// 通过Netty发送请求return (AbstractTransactionResponse) TmNettyRemotingClient.getInstance().sendSyncRequest(request);} catch (TimeoutException toe) {throw new TmTransactionException(TransactionExceptionCode.IO, "RPC timeout", toe);}}

具体图解如下:

在这里我们需要重点了解 GlobalTransactionScanner 这个类型,在这个类型中继承了一些接口和抽象类,这个类主要作用就是扫描有注解的Bean,并做AOP增强。

  • ApplicationContextAware:继承这个类型以后,需要实现其方法 setApplicationContext(),当Spring启动完成以后,会自动调用这个类型,将 ApplicationContextbean,也就是说, GlobalTransactionScanner 能够很自然的使用Spring环境

  • InitializingBean: 继承这个接口,需要实现 afterPropertiesSet() ,但凡是继承这个接口的类,在初始化的时候,当所有的 properties 设置完成以后,会执行这个方法

  • DisposableBean : 这个类,实现了一个 destroy() 这个方法是在销毁的时候去调用

  • AbstractAutoProxyCreator: 这个类是Spring实现AOP的一种方式,本质上是一个BeanPostProcessor ,在Bean初始化至去年,调用内部 createProxy() ,创建一个Bean的AOP代理Bean并返回,对Bean进行增强。

Seata数据源代理

在上面的环节中,我们讲解了Seata AT模式2PC的执行流程,那么现在我们就来带大家了解一下关于AT数据源代理的信息,这也是AT模式中非常关键的一个重要知识点,大家可以拿起小本子,记下来。

首先AT模式的核心主要分为一下两个

  • 开启全局事务,获取全局锁。
  • 解析SQL并写入undoLog中。

关于第一点我们已经分析清楚了,第二点就是关于AT模式如何解析SQL并写入undoLog中,但是在这之前,我们需要知道Seata是如何选择数据源,并进行数据源代理的。虽然全局事务拦截成功后最终还是执行了业务方法进行SQL提交和操作,但是由于Seata对数据源进行了代理,所以SQL的解析和undoLog的操作,是在数据源代理中进行完成的。

数据源代理是Seata中一个非常重要的知识点,在分布式事务运行过程中,undoLog的记录、资源的锁定,用户都是无感知的,因为这些操作都是数据源的代理中完成了,恰恰是这样,我们才要去了解,这样不仅有利于我们了解Seata的核心操作,还能对以后源码阅读有所帮助,因为其实很多底层代码都会去使用这样用户无感知的方式(代理)去实现。

同样,我们在之前的寻找源码入口的时候,通过我们项目中引入的jar找到一个 SeataAutoConfiguration 类,我们在里面找到一个SeataDataSourceBeanPostProcessor(),这个就是我们数据源代理的入口方法

我们进入SeataDataSourceBeanPostProcessor类里面,发现继承了一个 BeanPostProcessor ,这个接口我们应该很熟悉,这个是Sprng的拓展接口,所有的Bean对象,都有进入两个方法 postProcessAfterInitialization()postProcessBeforeInitialization() 这两个方法都是由 BeanPostProcessor提供的,这两个方法,一个是初始化之前执行Before。一个是在初始化之后执行After,主要用来对比我们的的Bean是否为数据源代理对象。

在这里我们需要关注到一个postProcessAfterInitialization.proxyDataSource() 方法,这个里面

private Object proxyDataSource(Object originBean) {DataSourceProxy dataSourceProxy = DataSourceProxyHolder.get().putDataSource((DataSource) originBean);if (this.useJdkProxy) {return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), SpringProxyUtils.getAllInterfaces(originBean), (proxy, method, args) -> handleMethodProxy(dataSourceProxy, method, args, originBean));} else {return Enhancer.create(originBean.getClass(), (MethodInterceptor) (proxy, method, args, methodProxy) -> handleMethodProxy(dataSourceProxy, method, args, originBean));}}

这里有一个DataSourceProxy代理对象,我们需要看的就是这个类,这个就是我们数据库代理的对象,我们从我们下载的源码项目中,搜索这个代理对象,当我们打开这个类的目录时发现,除了这个,还有ConnectionProxy 连接对象、StatementProxyPreparedStatementProxy SQL执行对象,这些都被Seata进行了代理,为什么要对这些都进行代理,代理的目的其实为了执行Seata的业务逻辑,生成undoLog,全局事务的开启,事务的提交回滚等操作

DataSourceProxy 具体做了什么,主要功能有哪些,我们来看一下。他在源码中是如何体现的,我们需要关注的是init()

public class DataSourceProxy extends AbstractDataSourceProxy implements Resource {private String resourceGroupId;private void init(DataSource dataSource, String resourceGroupId) {//资源组ID,默认是“default”这个默认值this.resourceGroupId = resourceGroupId;try (Connection connection = dataSource.getConnection()) {//根据原始数据源得到JDBC连接和数据库类型jdbcUrl = connection.getMetaData().getURL();dbType = JdbcUtils.getDbType(jdbcUrl);if (JdbcConstants.ORACLE.equals(dbType)) {userName = connection.getMetaData().getUserName();} else if (JdbcConstants.MARIADB.equals(dbType)) {dbType = JdbcConstants.MYSQL;}} catch (SQLException e) {throw new IllegalStateException("can not init dataSource", e);}initResourceId();DefaultResourceManager.get().registerResource(this);if (ENABLE_TABLE_META_CHECKER_ENABLE) {//如果配置开关打开,会定时在线程池不断更新表的元数据缓存信息tableMetaExecutor.scheduleAtFixedRate(() -> {try (Connection connection = dataSource.getConnection()) {TableMetaCacheFactory.getTableMetaCache(DataSourceProxy.this.getDbType()).refresh(connection, DataSourceProxy.this.getResourceId());} catch (Exception ignore) {}}, 0, TABLE_META_CHECKER_INTERVAL, TimeUnit.MILLISECONDS);}//Set the default branch type to 'AT' in the RootContext.RootContext.setDefaultBranchType(this.getBranchType());}}

从上面我们可以看出,他主要做了以下几点的增强:

  1. 给每个数据源标识资源组ID
  2. 如果打开配置,会有一个定时线程池定时更新表的元数据信息并缓存到本地
  3. 生成代理连接 ConnectionProxy 对象

在这三个增强功能里面,第三个是最重要的,在AT模式里面,会自动记录undoLog,资源锁定,都是通过ConnectionProxy完成的,除此之外 DataSrouceProxy重写了一个方法 getConnection,因为这里返回的是一个 ConnectionProxy,而不是原生的Connection

@Overridepublic ConnectionProxy getConnection() throws SQLException {Connection targetConnection = targetDataSource.getConnection();return new ConnectionProxy(this, targetConnection);}@Overridepublic ConnectionProxy getConnection(String username, String password) throws SQLException {Connection targetConnection = targetDataSource.getConnection(username, password);return new ConnectionProxy(this, targetConnection);}

ConnectionProxy

ConnectionProxy 继承 AbstractConnectionProxy ,在这个父类中有很多公用的方法,在这个父类有 PreparedStatementProxyStatementProxyDataSourceProxy

所以我们需要先来看一下AbstractConnectionProxy,因为这里封装了需要我们用到的通用方法和逻辑,在其中我们需要关注的主要在于 PreparedStatementProxyStatementProxy ,在这里的逻辑主要是数据源连接的步骤,连接获取,创建执行对象等等

@Overridepublic Statement createStatement() throws SQLException {//调用真实连接对象获取Statement对象Statement targetStatement = getTargetConnection().createStatement();//创建Statement的代理return new StatementProxy(this, targetStatement);}@Overridepublic PreparedStatement prepareStatement(String sql) throws SQLException {//获取数据库类型 mysql/oracleString dbType = getDbType();// support oracle 10.2+PreparedStatement targetPreparedStatement = null;//如果是AT模式且开启全局事务if (BranchType.AT == RootContext.getBranchType()) {List<SQLRecognizer> sqlRecognizers = SQLVisitorFactory.get(sql, dbType);if (sqlRecognizers != null && sqlRecognizers.size() == 1) {SQLRecognizer sqlRecognizer = sqlRecognizers.get(0);if (sqlRecognizer != null && sqlRecognizer.getSQLType() == SQLType.INSERT) {//获取表的元数据TableMeta tableMeta = TableMetaCacheFactory.getTableMetaCache(dbType).getTableMeta(getTargetConnection(),sqlRecognizer.getTableName(), getDataSourceProxy().getResourceId());//得到表的主键列名String[] pkNameArray = new String[tableMeta.getPrimaryKeyOnlyName().size()];tableMeta.getPrimaryKeyOnlyName().toArray(pkNameArray);targetPreparedStatement = getTargetConnection().prepareStatement(sql,pkNameArray);}}}if (targetPreparedStatement == null) {targetPreparedStatement = getTargetConnection().prepareStatement(sql);}//创建PreparedStatementProxy代理return new PreparedStatementProxy(this, targetPreparedStatement, sql);}

在这两个代理对象中,都用到了以下几个方法:

@Overridepublic ResultSet executeQuery(String sql) throws SQLException {this.targetSQL = sql;return ExecuteTemplate.execute(this, (statement, args) -> statement.executeQuery((String) args[0]), sql);}@Overridepublic int executeUpdate(String sql) throws SQLException {this.targetSQL = sql;return ExecuteTemplate.execute(this, (statement, args) -> statement.executeUpdate((String) args[0]), sql);}@Overridepublic boolean execute(String sql) throws SQLException {this.targetSQL = sql;return ExecuteTemplate.execute(this, (statement, args) -> statement.execute((String) args[0]), sql);}

在这些方法中都调用了 ExecuteTemplate.execute(),所以我们就看一下在 ExecuteTemplate类中具体是做了什么操作:

public class ExecuteTemplate {public static <T, S extends Statement> T execute(List<SQLRecognizer> sqlRecognizers, StatementProxy<S> statementProxy, StatementCallback<T, S> statementCallback, Object... args) throws SQLException {//如果没有全局锁,并且不是AT模式,直接执行SQLif (!RootContext.requireGlobalLock() && BranchType.AT != RootContext.getBranchType()) {// Just work as original statementreturn statementCallback.execute(statementProxy.getTargetStatement(), args);}//得到数据库类型- mysql/oracleString dbType = statementProxy.getConnectionProxy().getDbType();if (CollectionUtils.isEmpty(sqlRecognizers)) {//sqlRecognizers 为SQL语句的解析器,获取执行的SQL,通过它可以获得SQL语句表名、相关的列名、类型等信息,最后解析出对应的SQL表达式sqlRecognizers = SQLVisitorFactory.get(statementProxy.getTargetSQL(),dbType);}Executor<T> executor;if (CollectionUtils.isEmpty(sqlRecognizers)) {//如果seata没有找到合适的SQL语句解析器,那么便创建简单执行器PlainExecutor//PlainExecutor直接使用原生的Statment对象执行SQLexecutor = new PlainExecutor<>(statementProxy, statementCallback);} else {if (sqlRecognizers.size() == 1) {SQLRecognizer sqlRecognizer = sqlRecognizers.get(0);switch (sqlRecognizer.getSQLType()) {//新增case INSERT:executor = EnhancedServiceLoader.load(InsertExecutor.class, dbType,new Class[]{StatementProxy.class, StatementCallback.class, SQLRecognizer.class},new Object[]{statementProxy, statementCallback, sqlRecognizer});break;//修改case UPDATE:executor = new UpdateExecutor<>(statementProxy, statementCallback, sqlRecognizer);break;//删除case DELETE:executor = new DeleteExecutor<>(statementProxy, statementCallback, sqlRecognizer);break;//加锁case SELECT_FOR_UPDATE:executor = new SelectForUpdateExecutor<>(statementProxy, statementCallback, sqlRecognizer);break;//插入加锁case INSERT_ON_DUPLICATE_UPDATE:switch (dbType) {case JdbcConstants.MYSQL:case JdbcConstants.MARIADB:executor =new MySQLInsertOrUpdateExecutor(statementProxy, statementCallback, sqlRecognizer);break;default:throw new NotSupportYetException(dbType + " not support to INSERT_ON_DUPLICATE_UPDATE");}break;//原生default:executor = new PlainExecutor<>(statementProxy, statementCallback);break;}} else {//批量处理SQL语句executor = new MultiExecutor<>(statementProxy, statementCallback, sqlRecognizers);}}T rs;try {//执行rs = executor.execute(args);} catch (Throwable ex) {if (!(ex instanceof SQLException)) {// Turn other exception into SQLExceptionex = new SQLException(ex);}throw (SQLException) ex;}return rs;}}

ExecuteTemplate就一个 execute(),Seata将SQL执行委托给不同的执行器(模板),Seata提供了6种执行器也就是我们代码 case 中(INSERTUPDATEDELETESELECT_FOR_UPDATE,INSERT_ON_DUPLICATE_UPDATE),这些执行器的父类都是AbstractDMLBaseExecutor

  • UpdateExecutor: 执行update语句
  • InsertExecutor: 执行insert语句
  • DeleteExecutor: 执行delete语句
  • SelectForUpdateExecutor: 执行select for update语句
  • PlainExecutor: 执行普通查询语句
  • MultiExecutor: 复合执行器,在一条SQL语句中执行多条语句

关系图如下:

然后我们找到rs = executor.execute(args); 最终执行的方法,找到最***的父类BaseTransactionalExecutor.execute()

@Overridepublic T execute(Object... args) throws Throwable {String xid = RootContext.getXID();if (xid != null) {//获取XIDstatementProxy.getConnectionProxy().bind(xid);}//设置全局锁statementProxy.getConnectionProxy().setGlobalLockRequire(RootContext.requireGlobalLock());return doExecute(args);}

在根据doExecute(args);找到其中的重写方法 AbstractDMLBaseExecutor.doExecute()

@Overridepublic T doExecute(Object... args) throws Throwable {AbstractConnectionProxy connectionProxy = statementProxy.getConnectionProxy();//是否自动提交if (connectionProxy.getAutoCommit()) {return executeAutoCommitTrue(args);} else {return executeAutoCommitFalse(args);}}

对于数据库而言,本身都是自动提交的,所以我们进入executeAutoCommitTrue()

protected T executeAutoCommitTrue(Object[] args) throws Throwable {ConnectionProxy connectionProxy = statementProxy.getConnectionProxy();try {//设置为手动提交connectionProxy.changeAutoCommit();return new LockRetryPolicy(connectionProxy).execute(() -> {//调用手动提交方法,得到分支执行的最终结果T result = executeAutoCommitFalse(args);//执行提交connectionProxy.commit();return result;});} catch (Exception e) {// when exception occur in finally,this exception will lost, so just print it hereLOGGER.error("execute executeAutoCommitTrue error:{}", e.getMessage(), e);if (!LockRetryPolicy.isLockRetryPolicyBranchRollbackOnConflict()) {connectionProxy.getTargetConnection().rollback();}throw e;} finally {connectionProxy.getContext().reset();connectionProxy.setAutoCommit(true);}}

connectionProxy.changeAutoCommit()方法,修改为手动提交后,我们看来最关键的代码executeAutoCommitFalse()

protected T executeAutoCommitFalse(Object[] args) throws Exception {if (!JdbcConstants.MYSQL.equalsIgnoreCase(getDbType()) && isMultiPk()) {throw new NotSupportYetException("multi pk only support mysql!");}//获取前镜像TableRecords beforeImage = beforeImage();//执行具体业务T result = statementCallback.execute(statementProxy.getTargetStatement(), args);//获取执行数量int updateCount = statementProxy.getUpdateCount();//判断如果执行数量大于0if (updateCount > 0) {//获取后镜像TableRecords afterImage = afterImage(beforeImage);//暂存到undolog中,在Commit的时候保存到数据库prepareUndoLog(beforeImage, afterImage);}return result;}

我们再回到executeAutoCommitTrue中,去看看提交做了哪些操作connectionProxy.commit();

@Overridepublic void commit() throws SQLException {try {lockRetryPolicy.execute(() -> {//具体执行doCommit();return null;});} catch (SQLException e) {if (targetConnection != null && !getAutoCommit() && !getContext().isAutoCommitChanged()) {rollback();}throw e;} catch (Exception e) {throw new SQLException(e);}}

进入到doCommit()

private void doCommit() throws SQLException {//判断是否存在全局事务if (context.inGlobalTransaction()) {processGlobalTransactionCommit();} else if (context.isGlobalLockRequire()) {processLocalCommitWithGlobalLocks();} else {targetConnection.commit();}}

作为分布式事务,一定是存在全局事务的,所以我们进入 processGlobalTransactionCommit()

private void processGlobalTransactionCommit() throws SQLException {try {//注册分支事务register();} catch (TransactionException e) {recognizeLockKeyConflictException(e, context.buildLockKeys());}try {//写入数据库undologUndoLogManagerFactory.getUndoLogManager(this.getDbType()).flushUndoLogs(this);//执行原生提交 一阶段提交targetConnection.commit();} catch (Throwable ex) {LOGGER.error("process connectionProxy commit error: {}", ex.getMessage(), ex);report(false);throw new SQLException(ex);}if (IS_REPORT_SUCCESS_ENABLE) {report(true);}context.reset();}

其中register()方法就是注册分支事务的方法,同时还会将undoLog写入数据库和执行提交等操作

//注册分支事务,生成分支事务IDprivate void register() throws TransactionException {if (!context.hasUndoLog() || !context.hasLockKey()) {return;}//注册分支事务Long branchId = DefaultResourceManager.get().branchRegister(BranchType.AT, getDataSourceProxy().getResourceId(),null, context.getXid(), context.getApplicationData(), context.buildLockKeys());context.setBranchId(branchId);}

然后我们在回到processGlobalTransactionCommit中,看看写入数据库中的flushUndoLogs()

 @Overridepublic void flushUndoLogs(ConnectionProxy cp) throws SQLException {ConnectionContext connectionContext = cp.getContext();if (!connectionContext.hasUndoLog()) {return;}//获取XIDString xid = connectionContext.getXid();//获取分支IDlong branchId = connectionContext.getBranchId();BranchUndoLog branchUndoLog = new BranchUndoLog();branchUndoLog.setXid(xid);branchUndoLog.setBranchId(branchId);branchUndoLog.setSqlUndoLogs(connectionContext.getUndoItems());UndoLogParser parser = UndoLogParserFactory.getInstance();byte[] undoLogContent = parser.encode(branchUndoLog);if (LOGGER.isDebugEnabled()) {LOGGER.debug("Flushing UNDO LOG: {}", new String(undoLogContent, Constants.DEFAULT_CHARSET));}CompressorType compressorType = CompressorType.NONE;if (needCompress(undoLogContent)) {compressorType = ROLLBACK_INFO_COMPRESS_TYPE;undoLogContent = CompressorFactory.getCompressor(compressorType.getCode()).compress(undoLogContent);}//写入数据库具体位置insertUndoLogWithNormal(xid, branchId, buildContext(parser.getName(), compressorType), undoLogContent, cp.getTargetConnection());}

具体写入方法,此时我们使用的是MySql,所以执行的是MySql实现类MySQLUndoLogManager.insertUndoLogWithNormal()

@Overrideprotected void insertUndoLogWithNormal(String xid, long branchId, String rollbackCtx, byte[] undoLogContent, Connection conn) throws SQLException {insertUndoLog(xid, branchId, rollbackCtx, undoLogContent, State.Normal, conn);}//具体写入操作private void insertUndoLog(String xid, long branchId, String rollbackCtx, byte[] undoLogContent, State state, Connection conn) throws SQLException {try (PreparedStatement pst = conn.prepareStatement(INSERT_UNDO_LOG_SQL)) {pst.setLong(1, branchId);pst.setString(2, xid);pst.setString(3, rollbackCtx);pst.setBytes(4, undoLogContent);pst.setInt(5, state.getValue());pst.executeUpdate();} catch (Exception e) {if (!(e instanceof SQLException)) {e = new SQLException(e);}throw (SQLException) e;}}

具体流程如下所示:

Seata 服务端

我们找到Server.java 这里就是启动入口,在这个入口中找到协调者,因为TC整体的操作就是协调整体的全局事务

//默认协调者DefaultCoordinator coordinator = DefaultCoordinator.getInstance(nettyRemotingServer);

DefaultCoordinator类中我们找到 一个doGlobalBegin 这个就是处理全局事务开始的方法,以及全局提交 doGlobalCommit 和全局回滚 doGlobalRollback

//处理全局事务@Overrideprotected void doGlobalBegin(GlobalBeginRequest request, GlobalBeginResponse response, RpcContext rpcContext)throws TransactionException {//响应客户端xidresponse.setXid(core.begin(rpcContext.getApplicationId(), rpcContext.getTransactionServiceGroup(),request.getTransactionName(), request.getTimeout()));if (LOGGER.isInfoEnabled()) {LOGGER.info("Begin new global transaction applicationId: {},transactionServiceGroup: {}, transactionName: {},timeout:{},xid:{}",rpcContext.getApplicationId(), rpcContext.getTransactionServiceGroup(), request.getTransactionName(), request.getTimeout(), response.getXid());}}//处理全局提交@Overrideprotected void doGlobalCommit(GlobalCommitRequest request, GlobalCommitResponse response, RpcContext rpcContext)throws TransactionException {MDC.put(RootContext.MDC_KEY_XID, request.getXid());response.setGlobalStatus(core.commit(request.getXid()));}//处理全局回滚@Overrideprotected void doGlobalRollback(GlobalRollbackRequest request, GlobalRollbackResponse response,RpcContext rpcContext) throws TransactionException {MDC.put(RootContext.MDC_KEY_XID, request.getXid());response.setGlobalStatus(core.rollback(request.getXid()));}

在这里我们首先关注 doGlobalBegincore.begin()

@Overridepublic String begin(String applicationId, String transactionServiceGroup, String name, int timeout)throws TransactionException {//创建全局事务SessionGlobalSession session = GlobalSession.createGlobalSession(applicationId, transactionServiceGroup, name,timeout);MDC.put(RootContext.MDC_KEY_XID, session.getXid());//为Session重添加回调监听,SessionHolder.getRootSessionManager() 获取一个全局Session管理器DataBaseSessionManager//观察者设计模式,创建DataBaseSessionManagersession.addSessionLifecycleListener(SessionHolder.getRootSessionManager());//全局事务开始session.begin();// transaction start eventMetricsPublisher.postSessionDoingEvent(session, false);return session.getXid();}

然后我们在来看一下SessionHolder.getRootSessionManager()

/** * Gets root session manager. * 获取一个全局Session管理器 * @return the root session manager */public static SessionManager getRootSessionManager() {if (ROOT_SESSION_MANAGER == null) {throw new ShouldNeverHappenException("SessionManager is NOT init!");}return ROOT_SESSION_MANAGER;}public static void init(String mode) {if (StringUtils.isBlank(mode)) {mode = CONFIG.getConfig(ConfigurationKeys.STORE_SESSION_MODE,CONFIG.getConfig(ConfigurationKeys.STORE_MODE, SERVER_DEFAULT_STORE_MODE));}StoreMode storeMode = StoreMode.get(mode);//判断Seata模式,当前为DBif (StoreMode.DB.equals(storeMode)) {//通过SPI机制读取SessionManager接口实现类,读取的META-INF.services目录,在通过反射机制创建对象DataBaseSessionManagerROOT_SESSION_MANAGER = EnhancedServiceLoader.load(SessionManager.class, StoreMode.DB.getName());........}}

在这里他其实读取的是DB模式下 io.seata.server.session.SessionManager文件的内容

我们在回到begin方法中,去查看session.begin()

@Overridepublic void begin() throws TransactionException {//声明全局事务开始this.status = GlobalStatus.Begin;//开始时间this.beginTime = System.currentTimeMillis();//激活全局事务this.active = true;//将SessionManager放入到集合中,调用onBegin方法for (SessionLifecycleListener lifecycleListener : lifecycleListeners) {//调用父级抽象类的方法lifecycleListener.onBegin(this);}}

这里我们来看一下 onBegin() 方法,调用的是父级的方法,在这其中我们要关注 addGlobalSession() 方法,但是要注意,这里我们用的是db模式所以调用的是db模式的 DateBaseSessionManager

@Overridepublic void onBegin(GlobalSession globalSession) throws TransactionException {//这里调用的是DateBaseSessionManageraddGlobalSession(globalSession);}@Overridepublic void addGlobalSession(GlobalSession session) throws TransactionException {if (StringUtils.isBlank(taskName)) {//写入sessionboolean ret = transactionStoreManager.writeSession(LogOperation.GLOBAL_ADD, session);if (!ret) {throw new StoreException("addGlobalSession failed.");}} else {boolean ret = transactionStoreManager.writeSession(LogOperation.GLOBAL_UPDATE, session);if (!ret) {throw new StoreException("addGlobalSession failed.");}}}

然后在看查询其中关键的方法DataBaseTransactionStoreManager.writeSession()

 @Overridepublic boolean writeSession(LogOperation logOperation, SessionStorable session) {//第一次进入是写入 会进入当前方法//全局添加if (LogOperation.GLOBAL_ADD.equals(logOperation)) {return logStore.insertGlobalTransactionDO(SessionConverter.convertGlobalTransactionDO(session));//全局修改} else if (LogOperation.GLOBAL_UPDATE.equals(logOperation)) {return logStore.updateGlobalTransactionDO(SessionConverter.convertGlobalTransactionDO(session));//全局删除} else if (LogOperation.GLOBAL_REMOVE.equals(logOperation)) {return logStore.deleteGlobalTransactionDO(SessionConverter.convertGlobalTransactionDO(session));//分支添加} else if (LogOperation.BRANCH_ADD.equals(logOperation)) {return logStore.insertBranchTransactionDO(SessionConverter.convertBranchTransactionDO(session));//分支更新} else if (LogOperation.BRANCH_UPDATE.equals(logOperation)) {return logStore.updateBranchTransactionDO(SessionConverter.convertBranchTransactionDO(session));//分支移除} else if (LogOperation.BRANCH_REMOVE.equals(logOperation)) {return logStore.deleteBranchTransactionDO(SessionConverter.convertBranchTransactionDO(session));} else {throw new StoreException("Unknown LogOperation:" + logOperation.name());}}

我们就看第一次进去的方法logStore.insertGlobalTransactionDO(SessionConverter.convertGlobalTransactionDO(session));

 @Overridepublic boolean insertGlobalTransactionDO(GlobalTransactionDO globalTransactionDO) {String sql = LogStoreSqlsFactory.getLogStoreSqls(dbType).getInsertGlobalTransactionSQL(globalTable);Connection conn = null;PreparedStatement ps = null;try {int index = 1;conn = logStoreDataSource.getConnection();conn.setAutoCommit(true);ps = conn.prepareStatement(sql);ps.setString(index++, globalTransactionDO.getXid());ps.setLong(index++, globalTransactionDO.getTransactionId());ps.setInt(index++, globalTransactionDO.getStatus());ps.setString(index++, globalTransactionDO.getApplicationId());ps.setString(index++, globalTransactionDO.getTransactionServiceGroup());String transactionName = globalTransactionDO.getTransactionName();transactionName = transactionName.length() > transactionNameColumnSize ?transactionName.substring(0, transactionNameColumnSize) :transactionName;ps.setString(index++, transactionName);ps.setInt(index++, globalTransactionDO.getTimeout());ps.setLong(index++, globalTransactionDO.getBeginTime());ps.setString(index++, globalTransactionDO.getApplicationData());return ps.executeUpdate() > 0;} catch (SQLException e) {throw new StoreException(e);} finally {IOUtil.close(ps, conn);}}

在这里有一个 GlobalTransactionDO 对象,里面有xid、transactionId 等等,到这里是不是就很熟悉了、

还记得我们第一次使用Seata的时候会创建三张表

  1. branch_table 分支事务表
  2. global_table 全局事务表
  3. lock_table 全局锁表

而这里就是对应我们的global_table表,其他两个也是差不多,都是一样的操作

流程图如下:

总结

完整流程图:

对于Seata源码来说主要是了解从哪里入口以及核心点在哪里,遇到有疑问的,可以Debug,对于Seata AT模式,我们主要掌握的核心点是

  • 如何获取全局锁、开启全局事务
  • 解析SQL并写入undolog

围绕这两点去看的话,会有针对性一点,到这里我们的Seata源码就讲解完了,有疑问的小伙伴记得在下方留言。

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