Seata-AT模式

1.简介

概念：AT模式是一种无侵入的分布式事务解决方案，在 AT 模式下用户只需关注自己的“业务 SQL”，用户的 “业务 SQL” 作为一阶段，Seata 框架会自动生成事务的二阶段提交和回滚操作。

整体机制:

两阶段提交协议的演变：

一阶段：业务数据和回滚日志记录在同一个本地事务中提交，释放本地锁和连接资源。

二阶段：

提交异步化，非常快速地完成。

回滚通过一阶段的回滚日志进行反向补偿。

一阶段：

在一阶段中，Seata会拦截“业务SQL“，首先解析SQL语义，找到要更新的业务数据，在数据被更新前，保存下来"undo"，然后执行”业务SQL“更新数据，更新之后再次保存数据”redo“，最后生成行锁，这些操作都在本地数据库事务内完成，这样保证了一阶段的原子性。

二阶段：

相对一阶段，二阶段比较简单，负责整体的回滚和提交，如果之前的一阶段中有本地事务没有通过，那么就执行全局回滚，否在执行全局提交，回滚用到的就是一阶段记录的"undo Log"，通过回滚记录生成反向更新SQL并执行，以完成分支的回滚。当然事务完成后会释放所有资源和删除所有日志。

2.案例

设计2个服务，分别是seata-stock和seata-order

seata-order远程调用seata-stock

seata-stock服务：

数据库：

CREATE DATABASE `seata-stock` 
CREATE TABLE `stock` (
`product_id` int(2) NOT NULL AUTO_INCREMENT,
`count` int(2) DEFAULT NULL,
`money` int(2) DEFAULT NULL,
PRIMARY KEY (`product_id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

// seata用于回滚的日志表
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,
PRIMARY KEY (`id`),
UNIQUE KEY `ux_undo_log` (`xid`,`branch_id`)
) ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <parent>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-parent</artifactId>
     <version>2.6.4</version>
     <relativePath/> <!-- lookup parent from repository -->
 </parent>

 <groupId>com.zt.studydemo</groupId>
 <artifactId>seata-stock</artifactId>
 <version>0.0.1-SNAPSHOT</version>
 <name>seata-stock</name>
 <description>Demo project for Spring Boot</description>

 <properties>
     <java.version>1.8</java.version>
 </properties>

 <dependencies>
     <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
     </dependency>

     <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
     </dependency>

     <dependency>
         <groupId>org.mybatis.spring.boot</groupId>
         <artifactId>mybatis-spring-boot-starter</artifactId>
         <version>2.2.0</version>
     </dependency>

     <dependency>
         <groupId>com.alibaba</groupId>
         <artifactId>druid</artifactId>
         <version>1.2.9</version>
     </dependency>

     <dependency>
         <groupId>mysql</groupId>
         <artifactId>mysql-connector-java</artifactId>
         <version>8.0.26</version>
     </dependency>

     <dependency>
         <groupId>com.alibaba.cloud</groupId>
         <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
     </dependency>

     <dependency>
         <groupId>com.alibaba.cloud</groupId>
         <artifactId>spring-cloud-starter-alibaba-seata</artifactId>
     </dependency>
 </dependencies>

 <dependencyManagement>
     <dependencies>
         <dependency>
             <groupId>org.springframework.cloud</groupId>
             <artifactId>spring-cloud-dependencies</artifactId>
             <version>2021.0.1</version>
             <type>pom</type>
             <scope>import</scope>
         </dependency>

         <dependency>
             <groupId>com.alibaba.cloud</groupId>
             <artifactId>spring-cloud-alibaba-dependencies</artifactId>
             <version>2.2.7.RELEASE</version>
             <type>pom</type>
             <scope>import</scope>
         </dependency>
     </dependencies>
 </dependencyManagement>

 <build>
     <plugins>
         <plugin>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-maven-plugin</artifactId>
         </plugin>
     </plugins>
 </build>

</project>

yml：

server:
port: 8788

spring:
main:
 allow-circular-references: true
application:
 name: seata-stock
cloud:
 nacos:
   discovery:
     server-addr: 127.0.0.1:8848
 alibaba:
   seata:
     #事务分组，和seata-server中事务分组保持一致
     tx-service-group: mygroup
datasource:
 type: com.alibaba.druid.pool.DruidDataSource
 url: jdbc:mysql://127.0.0.1:3306/seata-stock?useUnicode=true&characterEncoding=UTF-8&useSSL=false&serverTimezone=Asia/Shanghai
 username: root
 password: root
 driver-class-name: com.mysql.cj.jdbc.Driver

seata:
#事务分组，和seata-server中事务分组保持一致，如果配置了这个上面的spring.cloud.alibaba.seata.tx-service-group就可以不用配置
#如果没有配置这个，应用程序会使用上面配置的事务分组来匹配
tx-service-group: mygroup
service:
 vgroup-mapping:
   #key是事务组名称 value要和服务端的机房名称保持一致
   mygroup: default

mybatis:
mapper-locations: classpath:mybatis/*.xml
type-aliases-package: com.zt.studydemo.seatastock.entity

StockMapper：

public interface StockMapper {

	/**
	 * 初始化库存
	 */
	void initStock();

	/**
     * 减库存操作
	 */
	void decrement();

}

StockMapper.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.zt.studydemo.seatastock.mapper.StockMapper" >

	<!-- 查询全部数据 -->
	<insert id="initStock">
		INSERT INTO stock (`count`, `money`) VALUES ('100','10');
	</insert>

    <!-- 查询全部数据 -->
	<update id="decrement">
		update stock set count = count-1
	</update>

</mapper>

StockService：

import com.zt.studydemo.seatastock.mapper.StockMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class StockService {

    @Autowired
    private StockMapper stockMapper;

    /**
     * 初始化库存
     */
    public void initStock(){
        stockMapper.initStock();
    }

    /**
     * 减库存操作
     */
    public void decrement(){
        stockMapper.decrement();
    }

}

StockController：

import com.zt.studydemo.seatastock.service.StockService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class StockController {

    @Autowired
    StockService stockService;

    @RequestMapping(value="/stock/initStock")
    public String initStock() {
        stockService.initStock();
        return "初始化库存";
    }

    @RequestMapping(value="/stock/decrement")
    public String decrement() {
        stockService.decrement();
        return "减库存";
    }
}

SeataStockApplication：

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

@SpringBootApplication
@EnableDiscoveryClient
@MapperScan("com.zt.studydemo.seatastock.mapper")
public class SeataStockApplication {

    public static void main(String[] args) {
        SpringApplication.run(SeataStockApplication.class, args);
    }

}

seata-order服务：

数据库：

CREATE DATABASE `seata-order`CREATE TABLE `order` (`product_id` int(11) NOT NULL AUTO_INCREMENT,`count` int(2) DEFAULT NULL,PRIMARY KEY (`product_id`)) ENGINE=InnoDB AUTO_INCREMENT=21 DEFAULT CHARSET=utf8;// seata用于回滚的日志表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,PRIMARY KEY (`id`),UNIQUE KEY `ux_undo_log` (`xid`,`branch_id`)) ENGINE=INNODB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

pom.xml：

<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"      xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent>     <groupId>org.springframework.boot</groupId>     <artifactId>spring-boot-starter-parent</artifactId>     <version>2.6.4</version>     <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.zt.studydemo</groupId> <artifactId>seata-order</artifactId> <version>0.0.1-SNAPSHOT</version> <name>seata-order</name> <description>Demo project for Spring Boot</description> <properties>     <java.version>1.8</java.version> </properties> <dependencies>     <dependency>         <groupId>org.springframework.boot</groupId>         <artifactId>spring-boot-starter-web</artifactId>     </dependency>     <dependency>         <groupId>org.springframework.boot</groupId>         <artifactId>spring-boot-starter-test</artifactId>         <scope>test</scope>     </dependency>     <dependency>         <groupId>org.mybatis.spring.boot</groupId>         <artifactId>mybatis-spring-boot-starter</artifactId>         <version>2.2.0</version>     </dependency>     <dependency>         <groupId>com.alibaba</groupId>         <artifactId>druid</artifactId>         <version>1.2.9</version>     </dependency>     <dependency>         <groupId>mysql</groupId>         <artifactId>mysql-connector-java</artifactId>         <version>8.0.26</version>     </dependency>     <dependency>         <groupId>com.alibaba.cloud</groupId>         <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>     </dependency>     <dependency>         <groupId>com.alibaba.cloud</groupId>         <artifactId>spring-cloud-starter-alibaba-seata</artifactId>     </dependency>     <dependency>         <groupId>org.springframework.cloud</groupId>         <artifactId>spring-cloud-starter-openfeign</artifactId>         <exclusions>             <exclusion>                 <groupId>org.springframework.cloud</groupId>                 <artifactId>spring-cloud-openfeign-core</artifactId>             </exclusion>         </exclusions>     </dependency>     <dependency>         <groupId>org.springframework.cloud</groupId>         <artifactId>spring-cloud-openfeign-core</artifactId>         <version>2.2.6.RELEASE</version>     </dependency> </dependencies> <dependencyManagement>     <dependencies>         <dependency>             <groupId>org.springframework.cloud</groupId>             <artifactId>spring-cloud-dependencies</artifactId>             <version>2021.0.1</version>             <type>pom</type>             <scope>import</scope>         </dependency>         <dependency>             <groupId>com.alibaba.cloud</groupId>             <artifactId>spring-cloud-alibaba-dependencies</artifactId>             <version>2.2.7.RELEASE</version>             <type>pom</type>             <scope>import</scope>         </dependency>     </dependencies> </dependencyManagement> <build>     <plugins>         <plugin>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-maven-plugin</artifactId>         </plugin>     </plugins> </build></project>

yml：

server:port: 8787spring:main: allow-circular-references: trueapplication: name: seata-ordercloud: nacos:   discovery:     server-addr: 127.0.0.1:8848 alibaba:   seata:     #事务分组，和seata-server中事务分组保持一致     tx-service-group: mygroupdatasource: type: com.alibaba.druid.pool.DruidDataSource url: jdbc:mysql://127.0.0.1:3306/seata-stock?useUnicode=true&characterEncoding=UTF-8&useSSL=false&serverTimezone=Asia/Shanghai username: root password: root driver-class-name: com.mysql.cj.jdbc.Driverseata:#事务分组，和seata-server中事务分组保持一致，如果配置了这个上面的spring.cloud.alibaba.seata.tx-service-group就可以不用配置#如果没有配置这个，应用程序会使用上面配置的事务分组来匹配tx-service-group: mygroupservice: vgroup-mapping:   #key是事务组名称 value要和服务端的机房名称保持一致   mygroup: defaultmybatis:mapper-locations: classpath:mybatis/*.xmltype-aliases-package: com.zt.studydemo.seataorder.entity

OrderMapper：

public interface OrderMapper { /**     * 创建订单     */    void createOrder();}

OrderMapper.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.zt.studydemo.seataorder.mapper.OrderMapper" >	<!-- 创建订单 -->	<insert id="createOrder">		INSERT INTO `order` (`count`) VALUES ('1');	</insert></mapper>

OpenFeignStockService：

import org.springframework.cloud.openfeign.FeignClient;import org.springframework.stereotype.Service;import org.springframework.web.bind.annotation.GetMapping;@Service@FeignClient("seata-stock")public interface OpenFeignStockService {    /**     * 此方法表示远程调用info/{id}接口     */    @GetMapping("stock/decrement")    public String decrement();}

OrderService：

import com.zt.studydemo.seataorder.mapper.OrderMapper;import com.zt.studydemo.seataorder.openfeign.OpenFeignStockService;import io.seata.spring.annotation.GlobalTransactional;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;@Servicepublic class OrderService {    @Autowired    private OrderMapper orderMapper;    @Autowired    private OpenFeignStockService openFeignStockService;    /**     * 创建订单     */    @GlobalTransactional// 开启分布式事务    public void createOrder(){        // 调用远程服务减库存        openFeignStockService.decrement();        // 异常点        int i = 1/0;        // 创建订单        orderMapper.createOrder();    }}

OrderController：

import com.zt.studydemo.seataorder.service.OrderService;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;@RestControllerpublic class OrderController {    @Autowired    OrderService orderService;    @RequestMapping(value="/order/create")    public String orderCreate() {        orderService.createOrder();        return "生成订单";    }}

SeataOrderApplication：

import org.mybatis.spring.annotation.MapperScan;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;import org.springframework.cloud.openfeign.EnableFeignClients;@SpringBootApplication@EnableDiscoveryClient@EnableFeignClients@MapperScan("com.zt.studydemo.seataorder.mapper")public class SeataOrderApplication {    public static void main(String[] args) {        SpringApplication.run(SeataOrderApplication.class, args);    }}

测试：

启动nacos，seata-server，seata-stock，seata-order

在OrderService.createOrder异常出设置断点

访问：http://127.0.0.1:8787/order/create

执行前库存表：

执行后库存表:

执行后undo_log表：

此时程序往下执行抛出异常，会发现库存表数据回滚，undo_log表中数据被清除

posted @ 2022-05-21 10:40 ZT丶阅读(144) 评论(0) 编辑收藏举报

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Seata-AT模式

1.简介

2.案例

公告