分布式事务之Seata中间件原理及流程详细分析

柔情只为你懂 2023-06-05 08:48 26阅读 0赞

转载自：[https://blog.csdn.net/f4761/article/details/89077400][https_blog.csdn.net_f4761_article_details_89077400]

## 背景 ##

在分布式系统中，分布式事务是一个必须要解决的问题，目前使用较多的是最终一致性方案。自年初阿里开源了Fescar（目前更名为Seata）后，该项目受到了极大的关注度。Seata以高性能和零侵入的方式为目标解决微服务领域的分布式事务难题，目前正处于快速迭代中，近期小目标是生产可用的Mysql版本。关于Seata的总体介绍，可以查看官方WIKI获得更多更全面的内容介绍。

本文主要基于spring cloud+spring jpa+spring cloud alibaba fescar+mysql+seata的结构，搭建一个分布式系统的demo，通过seata的debug日志和源代码，从client端（RM、TM）的角度分析说明其工作流程及原理。示例项目的完整代码已提交github，其中代码对应的类都添加了github连接，文中仅贴出关键部分。

[示例项目][Link 1]

## 相关概念 ##

XID：一个全局事务的唯一标识，由ip:port:sequence组成  
Transaction Coordinator (TC)： 事务协调器，维护全局事务的运行状态，负责协调并驱动全局事务的提交或回滚。  
Transaction Manager ™： 控制全局事务的边界，负责开启一个全局事务，并最终发起全局提交或全局回滚的决议。  
Resource Manager (RM)： 控制分支事务，负责分支注册、状态汇报，并接收事务协调器的指令，驱动分支（本地）事务的提交和回滚。

##    项目依赖 ##

seata使用XID表示一个分布式事务，XID需要在一次分布式事务请求所涉的系统中进行传递，从而向feacar-server发送分支事务的处理情况，以及接收feacar-server的commit、rollback指令。所以在分布式系统中使用seata要解决XID的传递问题。seata目前支持全版本的dubbo，对于spring cloud的分布式项目社区也提供了相应的实现

<dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-alibaba-fescar</artifactId>
    </dependency>

该组件实现了基于RestTemplate、Feign通讯时的XID传递功能，详细说明见[集成源码深度剖析：Fescar x Spring Cloud][Fescar x Spring Cloud]  
spring-cloud-alibaba-fescar内已包含了fescar-spring的依赖，所以可以不另外引入，查看完整的pom.xml.

## 业务逻辑 ##

业务逻辑是经典的下订单、扣余额、减库存流程。根据模块划分为三个独立的服务，且分别连接对应的数据库

订单：order-server  
账户：account-server  
库存：storage-server  
另外还有发起分布式事务的业务系统

业务：business-server  
项目结构如下图![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Y0NzYx_size_16_color_FFFFFF_t_70][]

## 配置文件 ##

seata的配置文件入口为[registry.conf][]查看代码[ConfigurationFactory][]得知目前还不能指定该配置文件，所以名称只能为registry.conf

private static final String REGISTRY_CONF = "registry.conf";
        
    public static final Configuration FILE_INSTANCE = new FileConfiguration(REGISTRY_CONF);

在registry中可以指定具体配置的形式，这里使用默认的file形式。在file.conf中有3部分配置内容

1 transport  
transport部分的配置对应[NettyServerConfig][]类，用于定义Netty的相关参与，client与server的通信使用的Netty  
2 service

service {
     #vgroup->rgroup
     vgroup_mapping.my_test_tx_group = "default"
     #配置Client连接TC的地址
     default.grouplist = "127.0.0.1:8091"
     #degrade current not support
     enableDegrade = false
     #disable
     是否启用seata的分布式事务
     disableGlobalTransaction = false
    }

//部分代码
    public class GlobalTransactionScanner{
    	private final boolean disableGlobalTransaction =
    	       ConfigurationFactory.getInstance().getBoolean("service.disableGlobalTransaction", false);
    	
    	public void afterPropertiesSet() {
            if (disableGlobalTransaction) {
                if (LOGGER.isInfoEnabled()) {
                    LOGGER.info("Global transaction is disabled.");
                }
                return;
            }
            initClient();
    	}
    }

3 client

client {
      #RM接收TC的commit通知后缓冲上限
      async.commit.buffer.limit = 10000
      lock {
        retry.internal = 10
        retry.times = 30
      }
    }

## 启动Server ##

前往[https://github.com/seata/seata/releases][https_github.com_seata_seata_releases] 下载最新版本的 Fescar Server  
解压之后的 bin 目录，执行

./fescar-server.sh 8091 ../data

启动成功输出

2019-04-09 20:27:24.637 INFO [main]c.a.fescar.core.rpc.netty.AbstractRpcRemotingServer.start:152 -Server started ...

## 启动Client ##

对于Spring boot项目，启动运行xxxApplication的main方法即可，seata的加载入口类位于[GlobalTransactionAutoConfiguration][]

@Configuration
    @EnableConfigurationProperties({FescarProperties.class})
    public class GlobalTransactionAutoConfiguration {
        private final ApplicationContext applicationContext;
        private final FescarProperties fescarProperties;
    
        public GlobalTransactionAutoConfiguration(ApplicationContext applicationContext, FescarProperties fescarProperties) {
            this.applicationContext = applicationContext;
            this.fescarProperties = fescarProperties;
        }
    
        @Bean
        public GlobalTransactionScanner globalTransactionScanner() {
            String applicationName = this.applicationContext.getEnvironment().getProperty("spring.application.name");
            String txServiceGroup = this.fescarProperties.getTxServiceGroup();
            if (StringUtils.isEmpty(txServiceGroup)) {
                txServiceGroup = applicationName + "-fescar-service-group";
                this.fescarProperties.setTxServiceGroup(txServiceGroup);
            }
    		
            return new GlobalTransactionScanner(applicationName, txServiceGroup);
        }
    }

可以看到支持一个配置项FescarProperties，用于配置事务分组名称

spring.cloud.alibaba.fescar.tx-service-group=my_test_tx_group

如果不指定则用spring.application.name+ -fescar-service-group生成一个名称，所以不指定spring.application.name启动会报错

@ConfigurationProperties("spring.cloud.alibaba.fescar")
    public class FescarProperties {
        private String txServiceGroup;
    
        public FescarProperties() {
        }
    
        public String getTxServiceGroup() {
            return this.txServiceGroup;
        }
    
        public void setTxServiceGroup(String txServiceGroup) {
            this.txServiceGroup = txServiceGroup;
        }
    }

有了applicationId和txServiceGroup则创建[GlobalTransactionScanner][]对象，主要看其中的initClient方法

private void initClient() {
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Initializing Global Transaction Clients ... ");
        }
        if (StringUtils.isNullOrEmpty(applicationId) || StringUtils.isNullOrEmpty(txServiceGroup)) {
            throw new IllegalArgumentException(
                "applicationId: " + applicationId + ", txServiceGroup: " + txServiceGroup);
        }
        //init TM
        TMClient.init(applicationId, txServiceGroup);
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info(
                "Transaction Manager Client is initialized. applicationId[" + applicationId + "] txServiceGroup["
                    + txServiceGroup + "]");
        }
        //init RM
        RMClient.init(applicationId, txServiceGroup);
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Resource Manager is initialized. applicationId[" + applicationId  + "] txServiceGroup["  + txServiceGroup + "]");
        }
    
        if (LOGGER.isInfoEnabled()) {
            LOGGER.info("Global Transaction Clients are initialized. ");
        }
    }

可以看到初始化了TMClient和RMClient，对于一个服务既可以是TM角色也可以是RM角色，至于什么时候是TM或者RM则要看在一次全局事务中@GlobalTransactional注解标注在哪。  
Client创建的结果是与TC的一个Netty连接，所以在启动日志中可以看到两个Netty Channel，其中也标明了transactionRole分别为TMROLE和RMROLE

NettyPool create channel to {"address":"127.0.0.1:8091","message":{"applicationId":"order-service","byteBuffer":{"char":"\u0000","direct":false,"double":0.0,"float":0.0,"int":0,"long":0,"readOnly":false,"short":0},"transactionServiceGroup":"hello-service-fescar-service-group","typeCode":101,"version":"0.4.0"},"transactionRole":"TMROLE"}
    NettyPool create channel to {"address":"127.0.0.1:8091","message":{"applicationId":"order-service","byteBuffer":{"char":"\u0000","direct":false,"double":0.0,"float":0.0,"int":0,"long":0,"readOnly":false,"short":0},"resourceIds":"jdbc:mysql://127.0.0.1:3306/db_order?useSSL=false","transactionServiceGroup":"hello-service-fescar-service-group","typeCode":103,"version":"0.4.0"},"transactionRole":"RMROLE"}
    Send:RegisterTMRequest{applicationId='order-service', transactionServiceGroup='hello-service-fescar-service-group'}
    Send:RegisterRMRequest{resourceIds='jdbc:mysql://127.0.0.1:3306/db_order?useSSL=false', applicationId='order-service', transactionServiceGroup='hello-service-fescar-service-group'}
    Receive:version=0.4.1,extraData=null,identified=true,resultCode=null,msg=null,messageId:2
    Receive:version=0.4.1,extraData=null,identified=true,resultCode=null,msg=null,messageId:1
    com.alibaba.fescar.core.rpc.netty.RmRpcClient@7904cd7c msgId:2, future :com.alibaba.fescar.core.protocol.MessageFuture@4107849f, body:version=0.4.1,extraData=null,identified=true,resultCode=null,msg=null
    com.alibaba.fescar.core.rpc.netty.TmRpcClient@68609034 msgId:1, future :com.alibaba.fescar.core.protocol.MessageFuture@527cc144, body:version=0.4.1,extraData=null,identified=true,resultCode=null,msg=null
    register success, cost 28 ms, version:0.4.1,role:TMROLE,channel:[id: 0xf45059d4, L:/127.0.0.1:63533 - R:/127.0.0.1:8091]
    register RM success. server version:0.4.1,channel:[id: 0xb7674b6a, L:/127.0.0.1:63534 - R:/127.0.0.1:8091]
    register success, cost 37 ms, version:0.4.1,role:RMROLE,channel:[id: 0xb7674b6a, L:/127.0.0.1:63534 - R:/127.0.0.1:8091]

日志中可以看到创建连接后，发送了注册请求，然后得到了结果相应，`RmRpcClient`、`TmRpcClient`成功实例化。

## TM处理流程 ##

在本例中，TM的角色是business-service,因为BusinessService的purchase方法标注了@GlobalTransactional

@Service
    public class BusinessService {
    
        @Autowired
        private StorageFeignClient storageFeignClient;
        @Autowired
        private OrderFeignClient orderFeignClient;
    
        @GlobalTransactional
        public void purchase(String userId, String commodityCode, int orderCount){
            storageFeignClient.deduct(commodityCode, orderCount);
    
            orderFeignClient.create(userId, commodityCode, orderCount);
        }
    }

GET请求127.0.0.1:8084/purchaseuserId=1001&commodityCode=2001&orderCount=1看看会发生什么

全局事务开启  
首先需要关注的是@GlobalTransactional注解的作用，它是在[GlobalTransactionalInterceptor][]中被拦截处理

//部分代码
    public class GlobalTransactionalInterceptor implements MethodInterceptor {
    	@Override
        public Object invoke(final MethodInvocation methodInvocation) throws Throwable {
            Class<?> targetClass = (methodInvocation.getThis() != null ? AopUtils.getTargetClass(methodInvocation.getThis()) : null);
            Method specificMethod = ClassUtils.getMostSpecificMethod(methodInvocation.getMethod(), targetClass);
            final Method method = BridgeMethodResolver.findBridgedMethod(specificMethod);
    
    		//获取方法GlobalTransactional注解
            final GlobalTransactional globalTransactionalAnnotation = getAnnotation(method, GlobalTransactional.class);
            final GlobalLock globalLockAnnotation = getAnnotation(method, GlobalLock.class);
            
            //如果方法有GlobalTransactional注解，则进行相应处理
            if (globalTransactionalAnnotation != null) {
                return handleGlobalTransaction(methodInvocation, globalTransactionalAnnotation);
            } else if (globalLockAnnotation != null) {
                return handleGlobalLock(methodInvocation);
            } else {
                return methodInvocation.proceed();
            }
        }
        
        //调用了TransactionalTemplate
    	private Object handleGlobalTransaction(final MethodInvocation methodInvocation,
                                               final GlobalTransactional globalTrxAnno) throws Throwable {
            try {
                return transactionalTemplate.execute(new TransactionalExecutor() {
                    @Override
                    public Object execute() throws Throwable {
                        return methodInvocation.proceed();
                    }
    
                    @Override
                    public int timeout() {
                        return globalTrxAnno.timeoutMills();
                    }
    
                    @Override
                    public String name() {
                        String name = globalTrxAnno.name();
                        if (!StringUtils.isNullOrEmpty(name)) {
                            return name;
                        }
                        return formatMethod(methodInvocation.getMethod());
                    }
                });
            } catch (TransactionalExecutor.ExecutionException e) {
                TransactionalExecutor.Code code = e.getCode();
                switch (code) {
                    case RollbackDone:
                        throw e.getOriginalException();
                    case BeginFailure:
                        failureHandler.onBeginFailure(e.getTransaction(), e.getCause());
                        throw e.getCause();
                    case CommitFailure:
                        failureHandler.onCommitFailure(e.getTransaction(), e.getCause());
                        throw e.getCause();
                    case RollbackFailure:
                        failureHandler.onRollbackFailure(e.getTransaction(), e.getCause());
                        throw e.getCause();
                    default:
                        throw new ShouldNeverHappenException("Unknown TransactionalExecutor.Code: " + code);
                }
            }
        }
    }

[TransactionalTemplate][]定义了TM对全局事务处理的标准步骤，注释写的比较清楚了

public class TransactionalTemplate {
    	public Object execute(TransactionalExecutor business) throws TransactionalExecutor.ExecutionException {
    
            // 1. get or create a transaction
            GlobalTransaction tx = GlobalTransactionContext.getCurrentOrCreate();
    
            try {
    
                // 2. begin transaction
                try {
                    triggerBeforeBegin();
                    tx.begin(business.timeout(), business.name());
                    triggerAfterBegin();
                } catch (TransactionException txe) {
                    throw new TransactionalExecutor.ExecutionException(tx, txe,
                        TransactionalExecutor.Code.BeginFailure);
    
                }
                Object rs = null;
                try {
    
                    // Do Your Business
                    rs = business.execute();
    
                } catch (Throwable ex) {
    
                    // 3. any business exception, rollback.
                    try {
                        triggerBeforeRollback();
                        tx.rollback();
                        triggerAfterRollback();
                        // 3.1 Successfully rolled back
                        throw new TransactionalExecutor.ExecutionException(tx, TransactionalExecutor.Code.RollbackDone, ex);
    
                    } catch (TransactionException txe) {
                        // 3.2 Failed to rollback
                        throw new TransactionalExecutor.ExecutionException(tx, txe,
                            TransactionalExecutor.Code.RollbackFailure, ex);
                    }
                }
                // 4. everything is fine, commit.
                try {
                    triggerBeforeCommit();
                    tx.commit();
                    triggerAfterCommit();
                } catch (TransactionException txe) {
                    // 4.1 Failed to commit
                    throw new TransactionalExecutor.ExecutionException(tx, txe,
                        TransactionalExecutor.Code.CommitFailure);
                }
    
                return rs;
            } finally {
                //5. clear
                triggerAfterCompletion();
                cleanUp();
            }
        }
    }

其中[DefaultGlobalTransaction][]的begin方法就是开启全局事务

@Override
    public void begin(int timeout, String name) throws TransactionException {
        //此处的角色判断有关键的作用
        //表明当前是全局事务的发起者（Launcher）还是参与者（Participant）
        //如果在分布式事务的下游系统方法中也加上GlobalTransactional注解
        //那么它的角色就是Participant，即会忽略后面的begin就退出了
        //而判断是发起者（Launcher）还是参与者（Participant）是根据当前上下文是否已存在XID来判断
        //没有XID的就是Launcher，已经存在XID的就是Participant
        if (role != GlobalTransactionRole.Launcher) {
            check();
            if (LOGGER.isDebugEnabled()) {
                LOGGER.debug("Ignore Begin(): just involved in global transaction [" + xid + "]");
            }
            return;
        }
        if (xid != null) {
            throw new IllegalStateException();
        }
        if (RootContext.getXID() != null) {
            throw new IllegalStateException();
        }
        //具体开启事务的方法，获取TC返回的XID
        xid = transactionManager.begin(null, null, name, timeout);
        status = GlobalStatus.Begin;
        RootContext.bind(xid);
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Begin a NEW global transaction [" + xid + "]");
        }
    }

[DefaultTransactionManager][]负责TM与TC通讯，发送begin、commit、rollback指令

@Override
    public String begin(String applicationId, String transactionServiceGroup, String name, int timeout)
        throws TransactionException {
        GlobalBeginRequest request = new GlobalBeginRequest();
        request.setTransactionName(name);
        request.setTimeout(timeout);
        GlobalBeginResponse response = (GlobalBeginResponse)syncCall(request);
        return response.getXid();
    }

至此拿到TC返回的XID一个全局事务就开启了，日志中也反应了上述流程

2019-04-09 13:46:57.417 DEBUG 31326 --- [nio-8084-exec-1] c.a.f.c.rpc.netty.AbstractRpcRemoting    : offer message: timeout=60000,transactionName=purchase(java.lang.String,java.lang.String,int)
    2019-04-09 13:46:57.417 DEBUG 31326 --- [geSend_TMROLE_1] c.a.f.c.rpc.netty.AbstractRpcRemoting    : write message:FescarMergeMessage timeout=60000,transactionName=purchase(java.lang.String,java.lang.String,int), channel:[id: 0xa148545e, L:/127.0.0.1:56120 - R:/127.0.0.1:8091],active?true,writable?true,isopen?true
    2019-04-09 13:46:57.418 DEBUG 31326 --- [lector_TMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Send:FescarMergeMessage timeout=60000,transactionName=purchase(java.lang.String,java.lang.String,int)
    2019-04-09 13:46:57.421 DEBUG 31326 --- [lector_TMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Receive:MergeResultMessage com.alibaba.fescar.core.protocol.transaction.GlobalBeginResponse@2dc480dc,messageId:1196
    2019-04-09 13:46:57.421 DEBUG 31326 --- [nio-8084-exec-1] c.a.fescar.core.context.RootContext      : bind 192.168.224.93:8091:2008502699
    2019-04-09 13:46:57.421 DEBUG 31326 --- [nio-8084-exec-1] c.a.f.tm.api.DefaultGlobalTransaction    : Begin a NEW global transaction [192.168.224.93:8091:2008502699]

全局事务创建后，就开始执行business.execute()，即业务代码`storageFeignClient.deduct(commodityCode, orderCount);`进入RM处理流程

## RM处理流程 ##

@GetMapping(path = "/deduct")
    public Boolean deduct(String commodityCode, Integer count){
        storageService.deduct(commodityCode,count);
        return true;
    }
    
    @Transactional
    public void deduct(String commodityCode, int count){
        Storage storage = storageDAO.findByCommodityCode(commodityCode);
        storage.setCount(storage.getCount()-count);
    
        storageDAO.save(storage);
    
        if (count == 5){
            throw new RuntimeException("storage branch exception");
        }
    }

storage的接口和service方法并未出现seata相关的代码和注解，那么它是如何加入到这次全局事务中的呢，答案是[ConnectionProxy][]中，这也是前面说为什么必须要使用DataSourceProxy的原因，通过DataSourceProxy才能在业务代码的事务提交时，seata通过这个切入点，来给TC发送rm的处理结果

由于业务代码本身的事务提交被ConnectionProxy代理，所以在提交本地事务时，实际执行的是ConnectionProxy的commit方法。

//部分代码
    public class ConnectionProxy extends AbstractConnectionProxy {
    	@Override
        public void commit() throws SQLException {
        	//如果当前是全局事务，则执行全局事务的提交
        	//判断是不是全局事务，就是看当前上下文是否存在XID
            if (context.inGlobalTransaction()) {
                processGlobalTransactionCommit();
            } else if (context.isGlobalLockRequire()) {
                processLocalCommitWithGlobalLocks();
            } else {
                targetConnection.commit();
            }
        }
        
    	private void processGlobalTransactionCommit() throws SQLException {
            try {
            	//首先是向TC注册RM，拿到TC分配的branchId
                register();
            } catch (TransactionException e) {
                recognizeLockKeyConflictException(e);
            }
    
            try {
                if (context.hasUndoLog()) {
                	//写入undolog
                    UndoLogManager.flushUndoLogs(this);
                }
    			
    			//提交本地事务，可以看到写入undolog和业务数据是在同一个本地事务中
                targetConnection.commit();
            } catch (Throwable ex) {
            	//向TC发送rm的事务处理失败的通知
                report(false);
                if (ex instanceof SQLException) {
                    throw new SQLException(ex);
                }
            }
    		//向TC发送rm的事务处理成功的通知
            report(true);
            context.reset();
        }
        
        //注册RM，构建request通过netty向TC发送指令
        //将返回的branchId存在上下文中
    	private void register() throws TransactionException {
            Long branchId = DefaultResourceManager.get().branchRegister(BranchType.AT, getDataSourceProxy().getResourceId(),
                    null, context.getXid(), null, context.buildLockKeys());
            context.setBranchId(branchId);
        }
    }

通过日志印证一下上面的流程

2019-04-09 21:57:48.341 DEBUG 38933 --- [nio-8081-exec-1] o.s.c.a.f.web.FescarHandlerInterceptor   : xid in RootContext null xid in RpcContext 192.168.0.2:8091:2008546211
    2019-04-09 21:57:48.341 DEBUG 38933 --- [nio-8081-exec-1] c.a.fescar.core.context.RootContext      : bind 192.168.0.2:8091:2008546211
    2019-04-09 21:57:48.341 DEBUG 38933 --- [nio-8081-exec-1] o.s.c.a.f.web.FescarHandlerInterceptor   : bind 192.168.0.2:8091:2008546211 to RootContext
    2019-04-09 21:57:48.386  INFO 38933 --- [nio-8081-exec-1] o.h.h.i.QueryTranslatorFactoryInitiator  : HHH000397: Using ASTQueryTranslatorFactory
    Hibernate: select storage0_.id as id1_0_, storage0_.commodity_code as commodit2_0_, storage0_.count as count3_0_ from storage_tbl storage0_ where storage0_.commodity_code=?
    Hibernate: update storage_tbl set count=? where id=?
    2019-04-09 21:57:48.673  INFO 38933 --- [nio-8081-exec-1] c.a.fescar.core.rpc.netty.RmRpcClient    : will connect to 192.168.0.2:8091
    2019-04-09 21:57:48.673  INFO 38933 --- [nio-8081-exec-1] c.a.fescar.core.rpc.netty.RmRpcClient    : RM will register :jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false
    2019-04-09 21:57:48.673  INFO 38933 --- [nio-8081-exec-1] c.a.f.c.rpc.netty.NettyPoolableFactory   : NettyPool create channel to {"address":"192.168.0.2:8091","message":{"applicationId":"storage-service","byteBuffer":{"char":"\u0000","direct":false,"double":0.0,"float":0.0,"int":0,"long":0,"readOnly":false,"short":0},"resourceIds":"jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false","transactionServiceGroup":"hello-service-fescar-service-group","typeCode":103,"version":"0.4.0"},"transactionRole":"RMROLE"}
    2019-04-09 21:57:48.677 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Send:RegisterRMRequest{resourceIds='jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false', applicationId='storage-service', transactionServiceGroup='hello-service-fescar-service-group'}
    2019-04-09 21:57:48.680 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Receive:version=0.4.1,extraData=null,identified=true,resultCode=null,msg=null,messageId:9
    2019-04-09 21:57:48.680 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.AbstractRpcRemoting    : com.alibaba.fescar.core.rpc.netty.RmRpcClient@7d61f5d4 msgId:9, future :com.alibaba.fescar.core.protocol.MessageFuture@186cd3e0, body:version=0.4.1,extraData=null,identified=true,resultCode=null,msg=null
    2019-04-09 21:57:48.680  INFO 38933 --- [nio-8081-exec-1] c.a.fescar.core.rpc.netty.RmRpcClient    : register RM success. server version:0.4.1,channel:[id: 0xd40718e3, L:/192.168.0.2:62607 - R:/192.168.0.2:8091]
    2019-04-09 21:57:48.680  INFO 38933 --- [nio-8081-exec-1] c.a.f.c.rpc.netty.NettyPoolableFactory   : register success, cost 3 ms, version:0.4.1,role:RMROLE,channel:[id: 0xd40718e3, L:/192.168.0.2:62607 - R:/192.168.0.2:8091]
    2019-04-09 21:57:48.680 DEBUG 38933 --- [nio-8081-exec-1] c.a.f.c.rpc.netty.AbstractRpcRemoting    : offer message: transactionId=2008546211,branchType=AT,resourceId=jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false,lockKey=storage_tbl:1
    2019-04-09 21:57:48.681 DEBUG 38933 --- [geSend_RMROLE_1] c.a.f.c.rpc.netty.AbstractRpcRemoting    : write message:FescarMergeMessage transactionId=2008546211,branchType=AT,resourceId=jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false,lockKey=storage_tbl:1, channel:[id: 0xd40718e3, L:/192.168.0.2:62607 - R:/192.168.0.2:8091],active?true,writable?true,isopen?true
    2019-04-09 21:57:48.681 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Send:FescarMergeMessage transactionId=2008546211,branchType=AT,resourceId=jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false,lockKey=storage_tbl:1
    2019-04-09 21:57:48.687 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Receive:MergeResultMessage BranchRegisterResponse: transactionId=2008546211,branchId=2008546212,result code =Success,getMsg =null,messageId:11
    2019-04-09 21:57:48.702 DEBUG 38933 --- [nio-8081-exec-1] c.a.f.rm.datasource.undo.UndoLogManager  : Flushing UNDO LOG: {"branchId":2008546212,"sqlUndoLogs":[{"afterImage":{"rows":[{"fields":[{"keyType":"PrimaryKey","name":"id","type":4,"value":1},{"keyType":"NULL","name":"count","type":4,"value":993}]}],"tableName":"storage_tbl"},"beforeImage":{"rows":[{"fields":[{"keyType":"PrimaryKey","name":"id","type":4,"value":1},{"keyType":"NULL","name":"count","type":4,"value":994}]}],"tableName":"storage_tbl"},"sqlType":"UPDATE","tableName":"storage_tbl"}],"xid":"192.168.0.2:8091:2008546211"}
    2019-04-09 21:57:48.755 DEBUG 38933 --- [nio-8081-exec-1] c.a.f.c.rpc.netty.AbstractRpcRemoting    : offer message: transactionId=2008546211,branchId=2008546212,resourceId=null,status=PhaseOne_Done,applicationData=null
    2019-04-09 21:57:48.755 DEBUG 38933 --- [geSend_RMROLE_1] c.a.f.c.rpc.netty.AbstractRpcRemoting    : write message:FescarMergeMessage transactionId=2008546211,branchId=2008546212,resourceId=null,status=PhaseOne_Done,applicationData=null, channel:[id: 0xd40718e3, L:/192.168.0.2:62607 - R:/192.168.0.2:8091],active?true,writable?true,isopen?true
    2019-04-09 21:57:48.756 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Send:FescarMergeMessage transactionId=2008546211,branchId=2008546212,resourceId=null,status=PhaseOne_Done,applicationData=null
    2019-04-09 21:57:48.758 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Receive:MergeResultMessage com.alibaba.fescar.core.protocol.transaction.BranchReportResponse@582a08cf,messageId:13
    2019-04-09 21:57:48.799 DEBUG 38933 --- [nio-8081-exec-1] c.a.fescar.core.context.RootContext      : unbind 192.168.0.2:8091:2008546211
    2019-04-09 21:57:48.799 DEBUG 38933 --- [nio-8081-exec-1] o.s.c.a.f.web.FescarHandlerInterceptor   : unbind 192.168.0.2:8091:2008546211 from RootContext

1 获取business-service传来的XID  
2 绑定XID到当前上下文中  
3 执行业务逻辑sql  
4 向TC创建本次RM的Netty连接  
5 向TC发送分支事务的相关信息  
6 获得TC返回的branchId  
7 记录Undo Log数据  
8 向TC发送本次事务PhaseOne阶段的处理结果  
9 从当前上下文中解绑XID

其中第1步和第9步，是在[FescarHandlerInterceptor][]中完成的，该类并不属于seata，而是spring-cloud-alibaba-fescar中对feign、rest支持的实现。bind和unbind XID到上下文中。到这里RM完成了PhaseOne阶段的工作，接着看PhaseTwo阶段的处理逻辑。

## 事务提交 ##

由于这次请求是正常流程无异常的，所以分支事务会正常commit。  
在storage-service启动时创建了与TC通讯的Netty连接，TC在获取各RM的汇报结果后，就会给各RM发送commit或rollback的指令

2019-04-09 21:57:49.813 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Receive:xid=192.168.0.2:8091:2008546211,branchId=2008546212,branchType=AT,resourceId=jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false,applicationData=null,messageId:1
    2019-04-09 21:57:49.813 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.AbstractRpcRemoting    : com.alibaba.fescar.core.rpc.netty.RmRpcClient@7d61f5d4 msgId:1, body:xid=192.168.0.2:8091:2008546211,branchId=2008546212,branchType=AT,resourceId=jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false,applicationData=null
    2019-04-09 21:57:49.814  INFO 38933 --- [atch_RMROLE_1_8] c.a.f.core.rpc.netty.RmMessageListener   : onMessage:xid=192.168.0.2:8091:2008546211,branchId=2008546212,branchType=AT,resourceId=jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false,applicationData=null
    2019-04-09 21:57:49.816  INFO 38933 --- [atch_RMROLE_1_8] com.alibaba.fescar.rm.AbstractRMHandler  : Branch committing: 192.168.0.2:8091:2008546211 2008546212 jdbc:mysql://127.0.0.1:3306/db_storage?useSSL=false null
    2019-04-09 21:57:49.816  INFO 38933 --- [atch_RMROLE_1_8] com.alibaba.fescar.rm.AbstractRMHandler  : Branch commit result: PhaseTwo_Committed
    2019-04-09 21:57:49.817  INFO 38933 --- [atch_RMROLE_1_8] c.a.fescar.core.rpc.netty.RmRpcClient    : RmRpcClient sendResponse branchStatus=PhaseTwo_Committed,result code =Success,getMsg =null
    2019-04-09 21:57:49.817 DEBUG 38933 --- [atch_RMROLE_1_8] c.a.f.c.rpc.netty.AbstractRpcRemoting    : send response:branchStatus=PhaseTwo_Committed,result code =Success,getMsg =null,channel:[id: 0xd40718e3, L:/192.168.0.2:62607 - R:/192.168.0.2:8091]
    2019-04-09 21:57:49.817 DEBUG 38933 --- [lector_RMROLE_1] c.a.f.c.rpc.netty.MessageCodecHandler    : Send:branchStatus=PhaseTwo_Committed,result code =Success,getMsg =null

从日志中可以看到

1.  收到XID=192.168.0.2:8091:2008546211,branchId=2008546212的commit通知
2.  执行commit动作
3.  将commit结果发送给TC，branchStatus为PhaseTwo\_Committed

具体看下执行commit的过程，在[AbstractRMHandler][]类的doBranchCommit方法之前是接收TC消息包装处理路由的过程

//拿到通知的xid、branchId等关键参数
    //然后调用RM的branchCommit
    protected void doBranchCommit(BranchCommitRequest request, BranchCommitResponse response) throws TransactionException {
        String xid = request.getXid();
        long branchId = request.getBranchId();
        String resourceId = request.getResourceId();
        String applicationData = request.getApplicationData();
        LOGGER.info("Branch committing: " + xid + " " + branchId + " " + resourceId + " " + applicationData);
        BranchStatus status = getResourceManager().branchCommit(request.getBranchType(), xid, branchId, resourceId, applicationData);
        response.setBranchStatus(status);
        LOGGER.info("Branch commit result: " + status);
    }

最终会将branceCommit的请求调用到[AsyncWorker][]的branchCommit方法。AsyncWorker的处理方式是seata架构的一个关键部分，大部分事务都是会正常提交的，所以在PhaseOne阶段就已经结束了，这样就可以将锁最快的释放。PhaseTwo阶段接收commit的指令后，异步处理即可。将PhaseTwo的时间消耗排除在一次分布式事务之外。

//部分代码
    public class AsyncWorker implements ResourceManagerInbound {
    
    	private static final List<Phase2Context> ASYNC_COMMIT_BUFFER = Collections.synchronizedList(
            new ArrayList<Phase2Context>());
            
        //将需要提交的XID加入list
    	@Override
        public BranchStatus branchCommit(BranchType branchType, String xid, long branchId, String resourceId, String applicationData) throws TransactionException {
            if (ASYNC_COMMIT_BUFFER.size() < ASYNC_COMMIT_BUFFER_LIMIT) {
                ASYNC_COMMIT_BUFFER.add(new Phase2Context(branchType, xid, branchId, resourceId, applicationData));
            } else {
                LOGGER.warn("Async commit buffer is FULL. Rejected branch [" + branchId + "/" + xid + "] will be handled by housekeeping later.");
            }
            return BranchStatus.PhaseTwo_Committed;
        }
    	
    	//通过一个定时任务消费list中的待提交XID
    	public synchronized void init() {
            LOGGER.info("Async Commit Buffer Limit: " + ASYNC_COMMIT_BUFFER_LIMIT);
            timerExecutor = new ScheduledThreadPoolExecutor(1,
                new NamedThreadFactory("AsyncWorker", 1, true));
            timerExecutor.scheduleAtFixedRate(new Runnable() {
                @Override
                public void run() {
                    try {
                        doBranchCommits();
                    } catch (Throwable e) {
                        LOGGER.info("Failed at async committing ... " + e.getMessage());
                    }
                }
            }, 10, 1000 * 1, TimeUnit.MILLISECONDS);
        }
    	
    	private void doBranchCommits() {
            if (ASYNC_COMMIT_BUFFER.size() == 0) {
                return;
            }
            Map<String, List<Phase2Context>> mappedContexts = new HashMap<>();
            Iterator<Phase2Context> iterator = ASYNC_COMMIT_BUFFER.iterator();
            
            //一次定时任务取出ASYNC_COMMIT_BUFFER中的所有待办数据
            //以resourceId作为key分组待办数据，resourceId就是一个数据库的连接url
            //在前面的日志中可以看到，目的是为了覆盖应用的多数据源问题
            while (iterator.hasNext()) {
                Phase2Context commitContext = iterator.next();
                List<Phase2Context> contextsGroupedByResourceId = mappedContexts.get(commitContext.resourceId);
                if (contextsGroupedByResourceId == null) {
                    contextsGroupedByResourceId = new ArrayList<>();
                    mappedContexts.put(commitContext.resourceId, contextsGroupedByResourceId);
                }
                contextsGroupedByResourceId.add(commitContext);
    
                iterator.remove();
    
            }
    
            for (Map.Entry<String, List<Phase2Context>> entry : mappedContexts.entrySet()) {
                Connection conn = null;
                try {
                    try {
                    	//根据resourceId获取数据源以及连接
                        DataSourceProxy dataSourceProxy = DataSourceManager.get().get(entry.getKey());
                        conn = dataSourceProxy.getPlainConnection();
                    } catch (SQLException sqle) {
                        LOGGER.warn("Failed to get connection for async committing on " + entry.getKey(), sqle);
                        continue;
                    }
                    List<Phase2Context> contextsGroupedByResourceId = entry.getValue();
                    for (Phase2Context commitContext : contextsGroupedByResourceId) {
                        try {
                        	//执行undolog的处理，即删除xid、branchId对应的记录
                            UndoLogManager.deleteUndoLog(commitContext.xid, commitContext.branchId, conn);
                        } catch (Exception ex) {
                            LOGGER.warn(
                                "Failed to delete undo log [" + commitContext.branchId + "/" + commitContext.xid + "]", ex);
                        }
                    }
    
                } finally {
                    if (conn != null) {
                        try {
                            conn.close();
                        } catch (SQLException closeEx) {
                            LOGGER.warn("Failed to close JDBC resource while deleting undo_log ", closeEx);
                        }
                    }
                }
            }
        }
    }

所以对于commit动作的处理，RM只需删除xid、branchId对应的undolog既可

事务回滚

对于rollback场景的触发有两种情况，

分支事务处理异常，即[ConnectionProxy][]中report(false)的情况  
TM捕获到下游系统上抛的异常，即发起全局事务标有@GlobalTransactional注解的方法捕获到的异常。在前面[TransactionalTemplate][]类的execute模版方法中，对business.execute()的调用进行了catch，catch后会调用rollback，由TM通知TC对应XID需要回滚事务

public void rollback() throws TransactionException {
       //只有Launcher能发起这个rollback
       if (role == GlobalTransactionRole.Participant) {
           // Participant has no responsibility of committing
           if (LOGGER.isDebugEnabled()) {
               LOGGER.debug("Ignore Rollback(): just involved in global transaction [" + xid + "]");
           }
           return;
       }
       if (xid == null) {
           throw new IllegalStateException();
       }
    
       status = transactionManager.rollback(xid);
       if (RootContext.getXID() != null) {
           if (xid.equals(RootContext.getXID())) {
               RootContext.unbind();
           }
       }
    
    }

TC汇总后向参与者发送rollback指令，RM在[AbstractRMHandler][]类的doBranchRollback方法中接收这个rollback的通知

protected void doBranchRollback(BranchRollbackRequest request, BranchRollbackResponse response) throws TransactionException {
        String xid = request.getXid();
        long branchId = request.getBranchId();
        String resourceId = request.getResourceId();
        String applicationData = request.getApplicationData();
        LOGGER.info("Branch rolling back: " + xid + " " + branchId + " " + resourceId);
        BranchStatus status = getResourceManager().branchRollback(request.getBranchType(), xid, branchId, resourceId, applicationData);
        response.setBranchStatus(status);
        LOGGER.info("Branch rollback result: " + status);
    }

然后将rollback请求传递到DataSourceManager类的branchRollback方法

public BranchStatus branchRollback(BranchType branchType, String xid, long branchId, String resourceId, String applicationData) throws TransactionException {
        //根据resourceId获取对应的数据源
        DataSourceProxy dataSourceProxy = get(resourceId);
        if (dataSourceProxy == null) {
            throw new ShouldNeverHappenException();
        }
        try {
            UndoLogManager.undo(dataSourceProxy, xid, branchId);
        } catch (TransactionException te) {
            if (te.getCode() == TransactionExceptionCode.BranchRollbackFailed_Unretriable) {
                return BranchStatus.PhaseTwo_RollbackFailed_Unretryable;
            } else {
                return BranchStatus.PhaseTwo_RollbackFailed_Retryable;
            }
        }
        return BranchStatus.PhaseTwo_Rollbacked;
    
    }

最终会执行[UndoLogManager][]类的undo方法，因为是纯jdbc操作代码比较长就不贴出来了，可以通过连接到github查看，说一下undo的具体流程

根据xid和branchId查找PhaseOne阶段提交的undolog  
如果找到了就根据undolog中记录的数据生成回放sql并执行，即还原PhaseOne阶段修改的数据  
第2步处理完后，删除该条undolog数据  
如果第1步没有找到对应的undolog，就插入一条状态为GlobalFinished的undolog.  
出现没找到的原因可能是PhaseOne阶段的本地事务异常了，导致没有正常写入。因为xid和branchId是唯一索引，所以第4步的插入，可以防止PhaseOne阶段后续又写入成功，那么PhaseOne阶段就会异常，这样业务数据也是没有提交成功的，数据最终是回滚了的效果

[https_blog.csdn.net_f4761_article_details_89077400]: https://blog.csdn.net/f4761/article/details/89077400
[Link 1]: https://github.com/fangls/seata-sample
[Fescar x Spring Cloud]: https://blog.csdn.net/yunqiinsight/article/details/88343096
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Y0NzYx_size_16_color_FFFFFF_t_70]: /images/20230601/ff808ddd7aeb48c4a6d8aba6e76d0e75.png
[registry.conf]: https://github.com/seata/seata/blob/develop/config/src/main/resources/registry.conf
[ConfigurationFactory]: https://github.com/seata/seata/blob/develop/config/src/main/java/com/alibaba/fescar/config/ConfigurationFactory.java
[NettyServerConfig]: https://github.com/seata/seata/blob/develop/core/src/main/java/com/alibaba/fescar/core/rpc/netty/NettyServerConfig.java
[https_github.com_seata_seata_releases]: https://github.com/seata/seata/releases
[GlobalTransactionAutoConfiguration]: https://github.com/spring-cloud-incubator/spring-cloud-alibaba/blob/finchley/spring-cloud-alibaba-fescar/src/main/java/org/springframework/cloud/alibaba/fescar/GlobalTransactionAutoConfiguration.java
[GlobalTransactionScanner]: https://github.com/seata/seata/blob/develop/spring/src/main/java/com/alibaba/fescar/spring/annotation/GlobalTransactionScanner.java
[GlobalTransactionalInterceptor]: https://github.com/seata/seata/blob/develop/spring/src/main/java/com/alibaba/fescar/spring/annotation/GlobalTransactionalInterceptor.java
[TransactionalTemplate]: https://github.com/seata/seata/blob/develop/tm/src/main/java/com/alibaba/fescar/tm/api/TransactionalTemplate.java
[DefaultGlobalTransaction]: https://github.com/seata/seata/blob/develop/tm/src/main/java/com/alibaba/fescar/tm/api/DefaultGlobalTransaction.java
[DefaultTransactionManager]: https://github.com/seata/seata/blob/develop/tm/src/main/java/com/alibaba/fescar/tm/DefaultTransactionManager.java
[ConnectionProxy]: https://github.com/seata/seata/blob/develop/rm-datasource/src/main/java/com/alibaba/fescar/rm/datasource/ConnectionProxy.java
[FescarHandlerInterceptor]: https://github.com/dongsheep/spring-cloud-alibaba/blob/master/spring-cloud-alibaba-fescar/src/main/java/org/springframework/cloud/alibaba/fescar/web/FescarHandlerInterceptor.java
[AbstractRMHandler]: https://github.com/seata/seata/blob/develop/rm/src/main/java/com/alibaba/fescar/rm/AbstractRMHandler.java
[AsyncWorker]: https://github.com/seata/seata/blob/develop/rm-datasource/src/main/java/com/alibaba/fescar/rm/datasource/AsyncWorker.java
[UndoLogManager]: https://github.com/seata/seata/blob/develop/rm-datasource/src/main/java/com/alibaba/fescar/rm/datasource/undo/UndoLogManager.java