16. SpringCloud Alibaba Seata处理分布式事务

16.1 分布式事务问题

分布式前:

单机单库没这个分布式事务问题,但是随着项目的业务不断增多,微服务与数据库的关系从1：1 -> 1：N -> N：N

分布式后:

单体应用被拆分成微服务应用，原来的三个模块被拆分成三个独立的应用，分别使用三个独立的数据源，
业务操作需要调用三个服务来完成。此时每个服务内部的数据一致性由本地事务来保证，但是全局的数据一致性问题没法保证。

一句话:一次业务操作需要跨多个数据源或需要跨多个系统进行远程调用，就会产生分布式事务问题

16.2 Seata简介

16.2.1 是什么

Seata是一款开源的分布式事务解决方案，致力于在微服务架构下提供高性能和简单易用的分布式事务服务。

官网地址:http://seata.io/zh-cn/

16.2.2 能干嘛

一个典型的分布式事务过程

1.分布式事务处理过程的一ID+三组件模型

• Transaction ID XID: 全局唯一的事务ID
• 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

2.处理过程

1. TM 向 TC 申请开启一个全局事务，全局事务创建成功并生成一个全局唯一的 XID；
2. XID 在微服务调用链路的上下文中传播；
3. RM 向 TC 注册分支事务，将其纳入 XID 对应全局事务的管辖；
4. TM 向 TC 发起针对 XID 的全局提交或回滚决议；
5. TC 调度 XID 下管辖的全部分支事务完成提交或回滚请求。

16.2.3 去哪下

发布说明: https://github.com/seata/seata/releases

16.2.4 怎么玩

单机版使用==@Transactional==,分布式事务使用==@GlobalTransactional==

SEATA 的分布式交易解决方案

16.3 Seata-Server安装

16.3.1 官网地址

http://seata.io/zh-cn/

16.3.2 下载版本

https://github.com/seata/seata/releases ,本次学习使用的是seata-server-0.9.0.zip

16.3.3 seata-server-0.9.0.zip解压到指定目录并修改conf目录下的file.conf配置文件

• 先备份原始file.conf文件
• 主要修改：自定义事务组名称+事务日志存储模式为db+数据库连接信息

file.conf 主要修改service模块和store模块

 service {###################给事务组起一个名字(啥都行,但是后期要在项目中进行对应)vgroup_mapping.my_test_tx_group = "fsp_tx_group"default.grouplist = "127.0.0.1:8091"enableDegrade = falsedisable = falsemax.commit.retry.timeout = "-1"max.rollback.retry.timeout = "-1"
}## transaction log store
store {## store mode: file、db
#############修改存储模式为数据库mode = "db"## file storefile {dir = "sessionStore"# branch session size , if exceeded first try compress lockkey, still exceeded throws exceptionsmax-branch-session-size = 16384# globe session size , if exceeded throws exceptionsmax-global-session-size = 512# file buffer size , if exceeded allocate new bufferfile-write-buffer-cache-size = 16384# when recover batch read sizesession.reload.read_size = 100# async, syncflush-disk-mode = async}## database storedb {## the implement of javax.sql.DataSource, such as DruidDataSource(druid)/BasicDataSource(dbcp) etc.datasource = "dbcp"## mysql/oracle/h2/oceanbase etc.db-type = "mysql"###########修改自己数据库的相关信息driver-class-name = "com.mysql.jdbc.Driver"url = "jdbc:mysql://127.0.0.1:3306/seata"user = "root"password = "root"min-conn = 1max-conn = 3global.table = "global_table"branch.table = "branch_table"lock-table = "lock_table"query-limit = 100}
}

16.3.4 mysql5.7数据库新建库seata

先建立数据库seata.建表db_store.sql在\seata-server-0.9.0\seata\conf目录里面

16.3.5 修改seata-server-0.9.0\seata\conf目录下的registry.conf配置文件

目的是：指明注册中心为nacos，及修改nacos连接信息

registry {# file 、nacos 、eureka、redis、zk、consul、etcd3、sofatype = "nacos"nacos {serverAddr = "localhost:8848"namespace = ""cluster = "default"}

16.3.6 启动seata-server

16.4 订单/库存/账户业务数据库准备

以下演示都需要先启动Nacos后启动Seata，保证两个都OK. Seata没启动报错no available server to connect

16.4.1 分布式事务业务说明

主要业务:下订单—>扣库存—>减账户(余额)

这里我们会创建三个服务，一个订单服务，一个库存服务，一个账户服务。

当用户下单时，会在订单服务中创建一个订单，然后通过远程调用库存服务来扣减下单商品的库存，
再通过远程调用账户服务来扣减用户账户里面的余额，最后在订单服务中修改订单状态为已完成。

该操作跨越三个数据库，有两次远程调用，很明显会有分布式事务问题。

16.4.2 创建业务数据库

• seata_order：存储订单的数据库；
• seata_storage：存储库存的数据库；
• seata_account：存储账户信息的数据库。
• 建库SQL

CREATE DATABASE seata_order;
CREATE DATABASE seata_storage;
CREATE DATABASE seata_account;

16.4.3 按照上述3库分别建对应业务表

• seata_order库下建t_order表
• seata_storage库下建t_storage 表
• seata_account库下建t_account 表
• 建表Sql

###########################t_order################################################
CREATE TABLE t_order (`id` BIGINT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,`user_id` BIGINT(11) DEFAULT NULL COMMENT '用户id',`product_id` BIGINT(11) DEFAULT NULL COMMENT '产品id',`count` INT(11) DEFAULT NULL COMMENT '数量',`money` DECIMAL(11,0) DEFAULT NULL COMMENT '金额',`status` INT(1) DEFAULT NULL COMMENT '订单状态：0：创建中；1：已完结' 
) ENGINE=INNODB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;SELECT * FROM t_order;
###########################t_storage#############################################
CREATE TABLE t_storage (`id` BIGINT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,`product_id` BIGINT(11) DEFAULT NULL COMMENT '产品id',`total` INT(11) DEFAULT NULL COMMENT '总库存',`used` INT(11) DEFAULT NULL COMMENT '已用库存',`residue` INT(11) DEFAULT NULL COMMENT '剩余库存'
) ENGINE=INNODB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;INSERT INTO seata_storage.t_storage(`id`, `product_id`, `total`, `used`, `residue`)
VALUES ('1', '1', '100', '0', '100');SELECT * FROM t_storage;
###########################t_account###############################################CREATE TABLE t_account (`id` BIGINT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY COMMENT 'id',`user_id` BIGINT(11) DEFAULT NULL COMMENT '用户id',`total` DECIMAL(10,0) DEFAULT NULL COMMENT '总额度',`used` DECIMAL(10,0) DEFAULT NULL COMMENT '已用余额',`residue` DECIMAL(10,0) DEFAULT '0' COMMENT '剩余可用额度'
) ENGINE=INNODB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;INSERT INTO seata_account.t_account(`id`, `user_id`, `total`, `used`, `residue`)  VALUES ('1', '1', '1000', '0', '1000');SELECT * FROM t_account;

16.4.4 按照上述3库分别建对应的回滚日志表

• 订单-库存-账户3个库下都需要建各自的回滚日志表
• \seata-server-0.9.0\seata\conf目录下的db_undo_log.sql

-- the table to store seata xid data
-- 0.7.0+ add context
-- you must to init this sql for you business databese. the seata server not need it.
-- 此脚本必须初始化在你当前的业务数据库中，用于AT 模式XID记录。与server端无关（注：业务数据库）
-- 注意此处0.3.0+ 增加唯一索引 ux_undo_log
DROP TABLE `undo_log`;CREATE TABLE `undo_log` (`id` BIGINT(20) NOT NULL AUTO_INCREMENT,`branch_id` BIGINT(20) NOT NULL,`xid` VARCHAR(100) NOT NULL,`context` VARCHAR(128) NOT NULL,`rollback_info` LONGBLOB NOT NULL,`log_status` INT(11) NOT NULL,`log_created` DATETIME NOT NULL,`log_modified` DATETIME NOT NULL,`ext` VARCHAR(100) DEFAULT NULL,PRIMARY KEY (`id`),UNIQUE KEY `ux_undo_log` (`xid`,`branch_id`)
) ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

16.4.5 最终效果

16.5 订单/库存/账户业务微服务准备

业务需求:下订单->减库存->扣余额->改(订单)状态

16.5.1 新建订单Order-Module

• 建Module—seata-order-service2001
• POM

    <dependencies><!--nacos--><dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId></dependency><!--seata--><dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-seata</artifactId><exclusions><!--排除自带的版本--><exclusion><artifactId>seata-all</artifactId><groupId>io.seata</groupId></exclusion><exclusion><groupId>io.seata</groupId><artifactId>seata-spring-boot-starter</artifactId></exclusion><exclusion><artifactId>spring-boot-starter</artifactId><groupId>org.springframework.boot</groupId></exclusion></exclusions></dependency><!--携带上使用的版本--><dependency><groupId>io.seata</groupId><artifactId>seata-all</artifactId><version>0.9.0</version><exclusions><exclusion><artifactId>fastjson</artifactId><groupId>com.alibaba</groupId></exclusion></exclusions></dependency><!--feign--><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId></dependency><!--web-actuator--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-actuator</artifactId></dependency><!--mysql-druid--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.47</version></dependency><dependency><groupId>com.alibaba</groupId><artifactId>druid-spring-boot-starter</artifactId><version>1.1.10</version></dependency><dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>2.0.0</version></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency>
</dependencies>

• YML

server:port: 2001spring:application:name: seata-order-servicecloud:alibaba:seata:#自定义事务组名称需要与seata-server中的对应tx-service-group: fsp_tx_groupnacos:discovery:server-addr: 192.168.174.128:8848datasource:driver-class-name: com.mysql.jdbc.Driverurl: jdbc:mysql://192.168.174.128:3306/seata_order?useSSL=falseusername: rootpassword: rootfeign:hystrix:enabled: falselogging:level:io:seata: infomybatis:mapperLocations: classpath:mapper/*.xmlconfiguration:map-underscore-to-camel-case: true

• file.conf以及registry.conf

file.conf :从seata软件中拷贝出来,然后需要修改的如下所示

.....................service {vgroup_mapping.fsp_tx_group = "default" #修改自定义事务组名称##################修改IP名称为使用的default.grouplist = "192.168.174.128:8091"enableDegrade = falsedisable = falsemax.commit.retry.timeout = "-1"max.rollback.retry.timeout = "-1"disableGlobalTransaction = false
}## transaction log store
store {## store mode: file、db#####修改模式为dbmode = "db"## file storefile {dir = "sessionStore"# branch session size , if exceeded first try compress lockkey, still exceeded throws exceptionsmax-branch-session-size = 16384# globe session size , if exceeded throws exceptionsmax-global-session-size = 512# file buffer size , if exceeded allocate new bufferfile-write-buffer-cache-size = 16384# when recover batch read sizesession.reload.read_size = 100# async, syncflush-disk-mode = async}## database storedb {## the implement of javax.sql.DataSource, such as DruidDataSource(druid)/BasicDataSource(dbcp) etc.datasource = "dbcp"## mysql/oracle/h2/oceanbase etc.db-type = "mysql"#############修改数据库的相关信息driver-class-name = "com.mysql.jdbc.Driver"url = "jdbc:mysql://192.168.174.128:3306/seata"user = "root"password = "root"min-conn = 1max-conn = 3global.table = "global_table"branch.table = "branch_table"lock-table = "lock_table"query-limit = 100}
}
........

registry.conf:从seata软件中拷贝出来,然后需要修改的如下所示

registry {# file 、nacos 、eureka、redis、zk、consul、etcd3、sofa###################### 类型修改为nacostype = "nacos"#############修改nacos的相关信息nacos {serverAddr = "192.168.174.128:8848"namespace = ""cluster = "default"}....
}config {# file、nacos 、apollo、zk、consul、etcd3type = "file"nacos {#############进行修改serverAddr = "192.168.174.128"namespace = ""}....
}
.....

• domain

CommonResult类

@Data
@AllArgsConstructor
@NoArgsConstructor
public class CommonResult<T>
{private Integer code;private String  message;private T       data;public CommonResult(Integer code, String message){this(code,message,null);}
}

Order类

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Order
{private Long id;private Long userId;private Long productId;private Integer count;private BigDecimal money;/*** 订单状态：0：创建中；1：已完结*/private Integer status;
}

• Dao接口及实现

OrderDao接口

@Mapper
public interface OrderDao {/*** 创建订单*/void create(Order order);/*** 修改订单金额*/void update(@Param("userId") Long userId, @Param("status") Integer status);
}

resources文件夹下新建mapper文件夹后添加

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.rg.cloudalibaba.dao.OrderDao"><!--便于后期进行扩展--><resultMap id="BaseResultMap" type="com.rg.cloudalibaba.domain.Order"><id column="id" property="id" jdbcType="BIGINT"/><result column="user_id" property="userId" jdbcType="BIGINT"/><result column="product_id" property="productId" jdbcType="BIGINT"/><result column="count" property="count" jdbcType="INTEGER"/><result column="money" property="money" jdbcType="DECIMAL"/><result column="status" property="status" jdbcType="INTEGER"/></resultMap><insert id="create">INSERT INTO t_order(id,user_id,product_id,`count`,money,`status`)VALUES(NULL,#{user_id},#{product_id},#{count},#{money},0);</insert><update id="update">UPDATE `t_order`SET `status` = 1WHERE user_id = #{user_id}AND `status` = #{status};</update></mapper>

• Service接口及实现

OrderService

public interface OrderService {/*** 创建订单*/void create(Order order);
}

OrderServiceImpl

@Service
@Slf4j
public class OrderServiceImpl implements OrderService {/*** 创建订单->调用库存服务扣减库存->调用账户服务扣减账户余额->修改订单状态* 简单说：* 下订单->减库存->减余额->改状态*/@Resourceprivate OrderDao orderDao;@Resourceprivate AccountService accountService;@Resourceprivate StorageService storageService;//@GlobalTransactional(name = "fsp-create-order",rollbackFor = Exception.class)public void create(Order order){log.info("--------------->下单开始");orderDao.create(order);//远程调用库存服务扣减库存log.info("----------------->order-service中扣减库存开始");storageService.decrease(order.getProductId(), order.getCount());log.info("----------------->order-service中扣减库存结束");//远程调用账户服务扣减余额log.info("----------------->order-service中扣减余额开始");accountService.decrease(order.getUserId(), order.getMoney());log.info("----------------->order-service中扣减余额结束");//修改订单状态log.info("----------------->order-service中修改订单状态开始");orderDao.update(order.getUserId(), 0);log.info("----------------->order-service中修改订单状态结束");log.info("--------------->下单结束");}}

StorageService

@FeignClient(value = "seata-storage-service")
public interface StorageService {/*** 扣减库存* @param productId* @param count* @return*/@PostMapping(value = "/storage/decrease")CommonResult decrease(@RequestParam("productId") Long productId, @RequestParam("count") Integer count);
}

AccountService

@FeignClient(value = "seata-account-service")
public interface AccountService {@PostMapping("/account/decrease")CommonResult decrease(@RequestParam("userId") Long userId, @RequestParam("money") BigDecimal money);
}

• controller

@RestController
public class OrderController {@Autowiredprivate OrderService orderService;/*** 创建订单*/@GetMapping("/order/create")public CommonResult create( Order order) {orderService.create(order);return new CommonResult(200, "订单创建成功!");}
}

• config

DataSourceProxyConfig:自定义数据源配置类

@Configuration
public class DataSourceProxyConfig {@Value("${mybatis.mapperLocations}")private String mapperLocations;@Bean@ConfigurationProperties(prefix = "spring.datasource")public DataSource druidDataSource(){return new DruidDataSource();}@Beanpublic DataSourceProxy dataSourceProxy(DataSource dataSource) {return new DataSourceProxy(dataSource);}@Beanpublic SqlSessionFactory sqlSessionFactoryBean(DataSourceProxy dataSourceProxy) throws Exception {SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();sqlSessionFactoryBean.setDataSource(dataSourceProxy);sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources(mapperLocations));sqlSessionFactoryBean.setTransactionFactory(new SpringManagedTransactionFactory());return sqlSessionFactoryBean.getObject();}
}

MyBatisConfig:数据源配置类

@Configuration
@MapperScan({"com.rg.cloudalibaba.dao"})
public class MyBatisConfig {
}

• 主启动

@EnableDiscoveryClient
@EnableFeignClients
@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)//取消数据源的自动创建
public class SeataOrderMainApp2001 {public static void main(String[] args) {SpringApplication.run(SeataOrderMainApp2001.class, args);}
}

16.5.2 新建库存Storage-Module

• 建Module—seata-storage-service2002
• POM—同order2001
• YML—同order2001,只是服务name以及连接的DB需要切换下
• file.conf和registry.conf—同order2001
• domain

CommonResult—同order2001

Storage类

@Data
public class Storage {private Long id;//产品idprivate Long productId;//总库存private Integer total;//已用库存private Integer used;//剩余库存private Integer residue;
}

• Dao接口及实现

StorageDao

@Mapper
public interface StorageDao {/*** 扣减库存*/void decrease(@Param("productId") Long productId, @Param("count") Integer count);
}

resources文件夹下新建mapper文件夹后添加StorageMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.rg.cloudalibaba.dao.StorageDao"><resultMap id="BaseResultMap" type="com.rg.cloudalibaba.domain.Storage"><id column="id" property="id" jdbcType="BIGINT"/><result column="product_id" property="productId" jdbcType="BIGINT"/><result column="total" property="total" jdbcType="INTEGER"/><result column="used" property="used" jdbcType="INTEGER"/><result column="residue" property="residue" jdbcType="INTEGER"/></resultMap><update id="decrease">UPDATE t_storageSET used = used+#{count},residue = residue - #{count}WHERE product_id = #{product_id};</update>
</mapper>

• Service接口及实现

StorageService类

public interface StorageService {/*** 扣减库存*/void decrease(Long productId, Integer count);
}

StorageServiceImpl类

@Service
@Slf4j
public class StorageServiceImpl implements StorageService {@Autowiredprivate StorageDao storageDao;@Overridepublic void decrease(Long productId, Integer count) {log.info("------------------------->storage-service中扣减库存开始");storageDao.decrease(productId,count);log.info("------------------------->storage-service中扣减库存结束");}
}

• controller

@RestController
public class StorageController {@Autowiredprivate StorageService storageService;@RequestMapping("/storage/decrease")public CommonResult decrease(Long productId,Integer count){storageService.decrease(productId,count);return new CommonResult(200, "扣减库存成功!");}
}

• Config—同order2001
• 主启动

@EnableDiscoveryClient
@EnableFeignClients
@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)//取消数据源的自动创建
public class SeataStorageMainApp2002 {public static void main(String[] args) {SpringApplication.run(SeataStorageMainApp2002.class, args);}
}

16.5.3 新建账户Account-Module

• 建Module—seata-account-service2003
• POM—同order2001
• YML—同order2001,只是服务name以及连接的DB需要切换下
• file.conf和registry.conf—同order2001
• domain

CommonResult—同order2001

Account类

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Account {private Long id;//用户idprivate Long userId;//总额度private BigDecimal total;//已用额度private BigDecimal used;//剩余额度private BigDecimal residue;
}

• Dao接口及实现

AccountDao

@Mapper
public interface AccountDao {/*** 扣减账户余额*/void decrease(@Param("userId") Long userId, @Param("money") BigDecimal money);
}

resources文件夹下新建mapper文件夹后添加AccountMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.rg.cloudalibaba.dao.AccountDao"><update id="decrease">UPDATE t_accountSET residue = residue - #{money},used = used+#{money}WHERE user_id = #{user_id};</update>
</mapper>

• Service接口及实现

AccountService

public interface AccountService {/*** 扣减账户余额* @param userId 用户id* @param money 金额*/void decrease(@RequestParam("userId") Long userId, @RequestParam("money") BigDecimal money);
}

AccountServiceImpl

@Service
@Slf4j
public class AccountServiceImpl implements AccountService {@Autowiredprivate AccountDao accountDao;@Overridepublic void decrease(Long userId, BigDecimal money) {log.info("-------------------account-service扣减账号余额开始");accountDao.decrease(userId,money);log.info("-------------------account-service扣减账号余额结束");}
}

• controller

@RestController
public class AccountController {@Autowiredprivate AccountService accountService;@RequestMapping("/account/decrease")CommonResult decrease(@RequestParam("userId") Long userId, @RequestParam("money") BigDecimal money){accountService.decrease(userId,money);return new CommonResult(200, "扣减账号余额成功!");}}

• Config配置—同order2001
• 主启动

@EnableDiscoveryClient
@EnableFeignClients
@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)//取消数据源的自动创建
public class SeataAccountMainApp2003 {public static void main(String[] args) {SpringApplication.run(SeataAccountMainApp2003.class, args);}
}

16.6 Test

16.6.1 数据库初始情况

SELECT * FROM seata_order.t_order

SELECT * FROM seata_storage.t_storage

SELECT * FROM seata_account.t_account;

16.6.2 正常下单

访问: http://localhost:2001/order/create?userId=1&productId=1&count=10&money=100

数据库情况:

16.6.3 超时异常，没加@GlobalTransactional

AccountServiceImpl添加超时

数据库情况:

故障情况:

当库存和账户金额扣减后，订单状态并没有设置为已经完成，没有从零改为1.而且由于feign的重试机制，账户余额还有可能被多次扣减

16.6.4 超时异常，添加@GlobalTransactional

AccountServiceImpl添加超时

OrderServiceImpl添加@GlobalTransactional

结果:下单后数据库数据并没有任何改变,记录都添加不进来

16.7 补充

16.7.1 Seata

• 2019年1月份蚂蚁金服和阿里巴巴共同开源的分布式事务解决方案
• Simple Extensible Autonomous Transaction Architecture，简单可扩展自治事务框架
• 2020起始，参加工作后用1.0以后的版本

16.7.2 再看TC/TM/RM三大组件

省略…

16.7.3 AT模式如何做到对业务的无侵入

• 是什么

• 一阶段加载

在一阶段，Seata 会拦截“业务 SQL”，
1 解析 SQL 语义，找到“业务 SQL”要更新的业务数据，在业务数据被更新前，将其保存成“before image”，
2 执行“业务 SQL”更新业务数据，在业务数据更新之后，
3 其保存成“after image”，最后生成行锁。
以上操作全部在一个数据库事务内完成，这样保证了一阶段操作的原子性。

• 二阶段提交

二阶段是顺利提交的情况
因为“业务 SQL”在一阶段已经提交至数据库，所以Seata框架只需将一阶段保存的快照数据和行锁删掉，完成数据清理即可。

• 二阶段回滚
  二阶段如果是回滚的话，Seata 就需要回滚一阶段已经执行的“业务 SQL”，还原业务数据。
  回滚方式便是用“before image”还原业务数据；但在还原前要首先要校验脏写，对比“数据库当前业务数据”和 “after image”，如果两份数据完全一致就说明没有脏写，可以还原业务数据，如果不一致就说明有脏写，出现脏写就需要转人工处理。

16.7.4 Debug过程分析