Microservices Seata distributed transactions

1. Distributed transaction problems

recommend : Distributed transactions （ The illustration + Seconds understand + In the history of the most complete ）
In the case of single machine and single library , There are local transactions to ensure data consistency ; But in a distributed architecture , The original single application is split into multiple microservice applications with independent data sources , The completion of a business scenario may require different micro service modules and different libraries . here The data consistency within each microservice module is guaranteed by local transactions , But there is no way to coordinate and guarantee the overall data consistency .
such as : The business logic for users to purchase goods , Need by 3 Micro services provide support .

• Warehousing services : Deduct the storage quantity from the given goods .
• Order service : Create an order based on purchase requirements .
• Account service : Deduct the balance from the user's account .

Architecture diagram :

In a word : A business operation needs to be called remotely across multiple data sources or systems , There will be distributed transaction problems .

2. Seata brief introduction

2.1 What is it?

Seata Is an open source distributed transaction solution , We are committed to providing high-performance and easy-to-use distributed transaction services under the microservice architecture .
→Seata Official website

2.2 Can do

A typical distributed transaction process : Global transaction ID + Three component model

• Transaction ID, Abbreviation XID. It is the globally unique transaction in the distribution ID.
• Transaction Coordinator , Abbreviation TC. Transaction coordinator , Maintain the running state of the global transaction , Responsible for coordinating and driving global transaction commit or rollback .
• Transaction Manager, Abbreviation TM. Transaction manager , Control the boundaries of global transactions , Responsible for opening a global transaction , And finally initiate the resolution of global commit or rollback .
• Resource Manager, Abbreviation RM. Explorer , Control branch transactions , Responsible for branch registration , Status report , And receive instructions from the transaction coordinator , Drive branch ( Local ) Transaction commit and rollback .

Model diagram :

Treatment process :

• TM towards TC Request to open a global transaction , The global transaction is created successfully and generates a globally unique XID;
• XID Propagate in the context of the microservice call link ;
• RM towards TC Register branch transactions , Be included in the XID Jurisdiction corresponding to global transaction ;
• TM towards TC Launch against XID The global commit or rollback resolution for ;
• TC Dispatch XID All branch transactions under the jurisdiction complete the commit or rollback request .

2.3 download

→Seata Download from the official website
→Seata stay GitHub Release notes for
→GitHub download Seata

2.4 How to use it?

We used to use Spring Notes provided @Transactionnal Turn on .
Seata It also provides us with the annotation to start the global transaction @GlobalTransactional.

We only need to use one on the business method @GlobalTransactional annotation .

3. Seata-Server install

The version I downloaded is seata-server-0.9.0 , You can choose an updated version .
take seata-server-0.9.0.zip Unzip to the specified directory and modify conf In the catalog file.conf The configuration file .( Backup first file.conf Modify the file later )

Modify the content : Custom transaction group name + The transaction log storage mode is db + Database connection information .
stay service Modify in the module Custom transaction group name

service {
  #vgroup->rgroup
  #  Custom transaction group name  fsp_tx_group,  Default default
  vgroup_mapping.my_test_tx_group = "fsp_tx_group"
  #only support single node
  default.grouplist = "127.0.0.1:8091"
  #degrade current not support
  enableDegrade = false
  #disable
  disable = false
  #unit ms,s,m,h,d represents milliseconds, seconds, minutes, hours, days, default permanent
  max.commit.retry.timeout = "-1"
  max.rollback.retry.timeout = "-1"
}

store Module modification The transaction log storage mode is db, And modify the database connection information .

store {
  ## store mode: file、db
  #  Transaction log storage mode 
  mode = "db"

  ## file store
  file {
    dir = "sessionStore"

    # branch session size , if exceeded first try compress lockkey, still exceeded throws exceptions
    max-branch-session-size = 16384
    # globe session size , if exceeded throws exceptions
    max-global-session-size = 512
    # file buffer size , if exceeded allocate new buffer
    file-write-buffer-cache-size = 16384
    # when recover batch read size
    session.reload.read_size = 100
    # async, sync
    flush-disk-mode = async
  }

  ## database store  Database connection information 
  db {
    ## the implement of javax.sql.DataSource, such as DruidDataSource(druid)/BasicDataSource(dbcp) etc.
    datasource = "dbcp"
    ## mysql/oracle/h2/oceanbase etc.
    db-type = "mysql"
    driver-class-name = "com.mysql.jdbc.Driver"
    url = "jdbc:mysql://127.0.0.1:3306/seata"
    user = "root"
    password = "root"
    min-conn = 1
    max-conn = 3
    global.table = "global_table"
    branch.table = "branch_table"
    lock-table = "lock_table"
    query-limit = 100
  }
}

stay mysql Created in seata library , Then create global transaction tables respectively global_table, Branch transaction table branch_table And transaction lock table lock_table. These three tables don't need to be designed by yourself , In download seata In bag conf There is a db_store.sql file , To mysql Just execute in the client .

-- the table to store GlobalSession data
drop table if exists `global_table`;
create table `global_table` (
  `xid` varchar(128)  not null,
  `transaction_id` bigint,
  `status` tinyint not null,
  `application_id` varchar(32),
  `transaction_service_group` varchar(32),
  `transaction_name` varchar(128),
  `timeout` int,
  `begin_time` bigint,
  `application_data` varchar(2000),
  `gmt_create` datetime,
  `gmt_modified` datetime,
  primary key (`xid`),
  key `idx_gmt_modified_status` (`gmt_modified`, `status`),
  key `idx_transaction_id` (`transaction_id`)
);

-- the table to store BranchSession data
drop table if exists `branch_table`;
create table `branch_table` (
  `branch_id` bigint not null,
  `xid` varchar(128) not null,
  `transaction_id` bigint ,
  `resource_group_id` varchar(32),
  `resource_id` varchar(256) ,
  `lock_key` varchar(128) ,
  `branch_type` varchar(8) ,
  `status` tinyint,
  `client_id` varchar(64),
  `application_data` varchar(2000),
  `gmt_create` datetime,
  `gmt_modified` datetime,
  primary key (`branch_id`),
  key `idx_xid` (`xid`)
);

-- the table to store lock data
drop table if exists `lock_table`;
create table `lock_table` (
  `row_key` varchar(128) not null,
  `xid` varchar(96),
  `transaction_id` long ,
  `branch_id` long,
  `resource_id` varchar(256) ,
  `table_name` varchar(32) ,
  `pk` varchar(36) ,
  `gmt_create` datetime ,
  `gmt_modified` datetime,
  primary key(`row_key`)
);

modify conf In the catalog registry.conf The configuration file ( Backup first ), Modify the registry configuration . Registry support nacos 、eureka、redis、zk、consuld etc. .

registry {
  # file 、nacos 、eureka、redis、zk、consul、etcd3、sofa
  #   The registry is amended to read nacos
  type = "nacos"

  nacos {
    serverAddr = "localhost:8848"
    namespace = ""
    cluster = "default"
  }
  ............  The complete configuration is omitted here 
}

Start... First nacos, Restart seata-server, Otherwise the newspaper no available server to connect.

/nacos/bin/startup.cmd
/seata-0.9.0/bin/seata-server.bat

4. Order / stock / Account business database preparation

Distributed transaction description , We need to create three services , Order service , Inventory service , Account service .
When a user places an order , The order service will create an order , Then the inventory service is called remotely to deduct the inventory of the ordered goods , Then deduct the account balance by calling the account service remotely , Finally, modify the order status to completed in the order service . This operation spans three databases , There are two remote calls , There's obviously a problem with distributed transactions .

scene : Place the order -> Deducting the inventory -> Deduct account balance
Three databases : Order database (seata_order), Inventory database (seata_storage), Account database (seata_account).

Business database SQL

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

stay seata_order Create an order table in the Library t_order.

 CREATE TABLE t_order (
  `id` BIGINT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,
  `user_id` BIGINT(11) DEFAULT NULL COMMENT ' user id',
  `product_id` BIGINT(11) DEFAULT NULL COMMENT ' product id',
  `count` INT(11) DEFAULT NULL COMMENT ' Number ',
  `money` DECIMAL(11,0) DEFAULT NULL COMMENT ' amount of money ',
  `status` INT(1) DEFAULT NULL COMMENT ' The order status ：0： In the create ;1： It's over ' 
) ENGINE=INNODB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;

stay seata_storage Create an inventory table in the Library t_storage

CREATE TABLE t_storage (
 `id` BIGINT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,
 `product_id` BIGINT(11) DEFAULT NULL COMMENT ' product id',
 `total` INT(11) DEFAULT NULL COMMENT ' Total inventory ',
 `used` INT(11) DEFAULT NULL COMMENT ' Used stock ',
 `residue` INT(11) DEFAULT NULL COMMENT ' Surplus stock '
) ENGINE=INNODB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
 
--  Initial stock  
INSERT INTO seata_storage.t_storage(`id`, `product_id`, `total`, `used`, `residue`)
VALUES ('1', '1', '100', '0', '100');

stay seata_account Create an account table in the Library t_account

CREATE TABLE t_account (
  `id` BIGINT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY COMMENT 'id',
  `user_id` BIGINT(11) DEFAULT NULL COMMENT ' user id',
  `total` DECIMAL(10,0) DEFAULT NULL COMMENT ' Total amount ',
  `used` DECIMAL(10,0) DEFAULT NULL COMMENT ' Used balance ',
  `residue` DECIMAL(10,0) DEFAULT '0' COMMENT ' The remaining amount available '
) ENGINE=INNODB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

--  Initialize account information  
INSERT INTO seata_account.t_account(`id`, `user_id`, `total`, `used`, `residue`)  VALUES ('1', '1', '1000', '0', '1000');

In the above three business databases seata_order, seata_storage, seata_account Create their own transaction rollback log tables . perform seata In bag conf In the catalog db_undo_log.sql file .

-- 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.
--  This script must be initialized in your current business database , be used for AT  Pattern XID Record . And server End independent （ notes ： Business database ）
--  Notice here 0.3.0+  Add unique index  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;

After the database table of each module is prepared , Take a look at the structure .

5. Order / stock / Account / Business microservice preparation

Business needs , Place the order -> Reduce inventory -> Deduct the balance -> Change order status

5.1 New order module

Create order module seata-order-service-2001, pom Dependency file .

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>atguigu-cloud-2020</artifactId>
        <groupId>com.atguigu.springcloud</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>seata-order-service-2001</artifactId>

    <dependencies>
    	<!-- Custom public dependencies -->
        <dependency>
            <groupId>com.atguigu.springcloud</groupId>
            <artifactId>cloud-api-commons</artifactId>
            <version>${project.version}</version>
        </dependency>
        <!--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>
                <exclusion>
                    <artifactId>seata-all</artifactId>
                    <groupId>io.seata</groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>io.seata</groupId>
            <artifactId>seata-all</artifactId>
            <version>0.9.0</version>
        </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>5.1.37</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.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>
</project>

yml To configure

server:
  port: 2001

spring:
  application:
    name: seata-order-service
  cloud:
    alibaba:
      seata:
        # The custom transaction group name needs to match seata-server Corresponding to in 
        tx-service-group: fsp_tx_group
    nacos:
      discovery:
        server-addr: localhost:8848
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/seata_order?serverTimezone=Asia/Shanghai
    username: root
    password: root
feign:
  hystrix:
    enabled: false
logging:
  level:
    io:
      seata: info
#  Custom properties  
mybatis:
  mapperLocations: classpath:mapper/*.xml

take file.conf and registry.conf Copy to the project classpath .

Then make a change file.conf Transaction group name and seata-server The configuration in is consistent .

service {
  #vgroup->rgroup
  # Modify custom transaction group name ,  It's hard for me to change , Use the default default.  Mapping to seata-server Of fsp_tx_group
  vgroup_mapping.fsp_tx_group = "default"   
  #only support single node
  default.grouplist = "127.0.0.1:8091"
  #degrade current not support
  enableDegrade = false
  #disable
  disable = false
  #unit ms,s,m,h,d represents milliseconds, seconds, minutes, hours, days, default permanent
  max.commit.retry.timeout = "-1"
  max.rollback.retry.timeout = "-1"
}

To write Order Order entity class

/** *  Class description ： Order  */
@NoArgsConstructor
@AllArgsConstructor
@Data
@Builder
public class Order {
    

    private Long id;

    private Long userId;

    private Long productId;

    private Integer count;

    private BigDecimal money;
    /** *  The order status ：0： In the create ;1： It's over  */
    private Integer status;
}

establish OrderDao Interface , Use @Mapper annotations .

@Mapper
public interface OrderDao {
    
    /** *  Create order  */
    void create(Order order);
    /** *  Modify order status  */
    void update(@Param("userId") Long userId, @Param("status") Integer status);
}

establish OrderDao Interface mapping file , 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.atguigu.springcloud.dao.OrderDao">

    <resultMap id="BaseResultMap" type="com.atguigu.springcloud.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" parameterType="com.atguigu.springcloud.domain.Order">
        INSERT INTO `t_order` (`id`, `user_id`, `product_id`, `count`, `money`, `status`)
        VALUES (NULL, #{userId}, #{productId}, #{count}, #{money}, 0);
    </insert>

    <update id="update">
        UPDATE `t_order`
        SET status = 1
        WHERE user_id = #{userId} AND status = #{status};
    </update>
</mapper>

establish Service And Realization

public interface OrderService {
    
    /** *  Create order  */
    void create(Order order);
}

/** *  Class description ： Remotely call inventory service to deduct inventory  */
@FeignClient(value = "seata-storage-service")
public interface StorageService {
    
    @PostMapping(value = "/storage/decrease")
    CommonResult decrease(@RequestParam("productId") Long productId, @RequestParam("count") Integer count);
}

/** *  Class description ： Remote call account service deduction balance  */
@FeignClient(value = "seata-account-service")
public interface AccountService {
    
    @PostMapping(value = "/account/decrease")
    CommonResult decrease(@RequestParam("userId") Long userId, @RequestParam("money") BigDecimal money);
}

/** *  Class description ： Order service business logic class  */
@Service
@Slf4j
public class OrderServiceImpl implements OrderService {
    

    @Resource
    private OrderDao orderDao;

    @Resource
    private StorageService storageService;

    @Resource
    private AccountService accountService;

    /** *  Create order -> Call inventory service to deduct inventory -> Call the account service to deduct the account balance -> Modify order status  *  In short ： *  Place the order -> Reduce inventory -> Less balance -> Change state  */
    @Override
   // @GlobalTransactional(name = "fsp-create-order", rollbackFor = Exception.class)
    public void create(Order order) {
    
    
        log.info("-------> Order start ");
        // This application creates orders 
        orderDao.create(order);
        // Call inventory service remotely to deduct inventory 
        log.info("------->order-service The deduction of inventory starts ");
        storageService.decrease(order.getProductId(), order.getCount());
        log.info("------->order-service After deducting the inventory from the inventory, the end ");

        // Remote call account service deduction balance 
        log.info("------->order-service The deduction balance starts ");
        accountService.decrease(order.getUserId(), order.getMoney());
        log.info("------->order-service End of deduction balance in ");

        // Change order status to completed 
        log.info("------->order-service Start by modifying the order status in ");
        orderDao.update(order.getProductId(), 0);
        log.info("------->order-service End of modifying order status in ");
        log.info("-------> End of order ");
    }
}

To write controller

@RestController
public class OrderController {
    
    @Autowired
    private OrderService orderService;

    /** *  Create order  */
    @GetMapping("/order/create")
    public CommonResult create(Order order) {
    
        orderService.create(order);
        return new CommonResult(200, " Order created successfully !");
    }
}

MybatisConfig Configure scan mapper Interface package .

@Configuration
@MapperScan(value = "com.atguigu.springcloud.dao")
public class MyBatisConfig {
    
}

Configure proxy data sources

/** *  Class description ：  Use Seata Proxy data sources  * io.seata.rm.datasource.DataSourceProxy */
@Configuration
public class DataSourceProxyConfig {
    
    @Value("${mybatis.mapper-locations}")
    private String mapperLocations;

    @Bean
    @ConfigurationProperties(prefix = "spring.datasource")
    public DataSource druidDataSource() {
    
        return new DruidDataSource();
    }

    @Bean
    public DataSourceProxy dataSourceProxy(DataSource dataSource) {
    
        return new DataSourceProxy(dataSource);
    }

    @Bean
    public 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();
    }
}

Create the main startup class

//  Exclude automatic configuration of data sources , Use a custom data source 
@SpringBootApplication(exclude = DataSourceAutoConfiguration.class) 
@EnableDiscoveryClient
@EnableFeignClients
public class SeataOrderMainApp2001 {
    
    public static void main(String[] args) {
    
        SpringApplication.run(SeataOrderMainApp2001.class);
    }
}

5.2 Create a new inventory module

Follow the same steps above to create the inventory micro service module seata-storage-service-2002
Take out the different ones separately .
Inventory entity class Storage

@AllArgsConstructor
@NoArgsConstructor
@Data
@Builder
public class Storage {
    

    private Long id;

    /** *  product id */
    private Long productId;

    /** *  Total inventory  */
    private Integer total;

    /** *  Used stock  */
    private Integer used;

    /** *  Surplus stock  */
    private Integer residue;
}

Deduction inventory logic . StorageController

@RestController
public class StorageController {
    
    @Autowired
    private StorageService storageService;
    /** *  Deducting the inventory  */
    @RequestMapping("/storage/decrease")
    public CommonResult decrease(Long productId, Integer count) {
    

        storageService.decrease(productId, count);
        return new CommonResult(200, " Inventory reduction succeeded ！");
    }
}

StorageServiceImpl

@Service
@Slf4j
public class StorageServiceImpl implements StorageService {
    
    @Resource
    private StorageDao storageDao;
    /** *  Deducting the inventory  */
    @Override
    public void decrease(Long productId, Integer count) {
    
        log.info("------->storage-service The deduction of inventory starts ");
        storageDao.decrease(productId, count);
        log.info("------->storage-service After deducting the inventory from the inventory, the end ");
    }
}

StorageDao

@Mapper
public interface StorageDao {
    
    /** *  Deducting the inventory  */
    void decrease(@Param("productId") Long productId, @Param("count") Integer count);
}

StorageMapper.xml The mapping file

<?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.atguigu.springcloud.dao.StorageDao">
    <resultMap id="BaseResultMap" type="com.atguigu.springcloud.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_storage
        SET used    = used + #{count},
            residue = residue - #{count}
        WHERE product_id = #{productId}
    </update>
</mapper>

5.3 Create a new account module

Create the account micro service module in the same steps seata-account-service-2003
The logic of deducting the account balance is taken out separately . AccountController

@RestController
public class AccountController {
    
    @Resource
    private AccountService accountService;
    /** *  Deduct account balance  */
    @RequestMapping("/account/decrease")
    public CommonResult decrease(@RequestParam("userId") Long userId, @RequestParam("money") BigDecimal money) {
    
        accountService.decrease(userId, money);
        return new CommonResult(200, " Deduct account balance successfully ！");
    }
}

AccountServiceImpl

@Service
@Slf4j
public class AccountServiceImpl implements AccountService {
    
    @Resource
    private AccountDao accountDao;
    /** *  Deduct account balance  */
    @Override
    public void decrease(Long userId, BigDecimal money) {
    
        log.info("------->account-service Start by deducting the account balance ");
        accountDao.decrease(userId, money);
        log.info("------->account-service The account balance is deducted from the account to end ");
    }
}

AccountDao

@Mapper
public interface AccountDao {
    
    /** *  Deduct account balance  */
    void decrease(@Param("userId") Long userId, @Param("money") BigDecimal money);
}

AccountMapper.xml The mapping file

<?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.atguigu.springcloud.dao.AccountDao">
    <resultMap id="BaseResultMap" type="com.atguigu.springcloud.domain.Account">
        <id column="id" property="id" jdbcType="BIGINT"/>
        <result column="user_id" property="userId" jdbcType="BIGINT"/>
        <result column="total" property="total" jdbcType="DECIMAL"/>
        <result column="used" property="used" jdbcType="DECIMAL"/>
        <result column="residue" property="residue" jdbcType="DECIMAL"/>
    </resultMap>

    <update id="decrease">
        UPDATE t_account
        SET
          residue = residue - #{money},used = used + #{money}
        WHERE
          user_id = #{userId};
    </update>
</mapper>

6. Distributed transaction testing

6.1 Data initialization

First, query the initial data state of the database .
SELECT * FROM seata_order.t_order; There was no initial order

SELECT * FROM seata_storage.t_storage; stock 100, Use 0, The remaining 100.

SELECT * FROM seata_account.t_account; balance 1000, Use 0, The remaining 1000.

6.2 Forward test

First , start-up Nacos, start-up Seata-server, Start the service module .
Test a normal order . visit http://localhost:2001/order/create?userId=1&productId=1&count=10&money=10. Order purchase 10 A product , common 10 element .

Without exception , The data results of each module are normal . An order data has been added to the order library and the order status has been completed , There is still left 90 Inventory , The balance of the account remains 990 element .

6.3 No distributed transaction reverse test

Order service#create Method without adding @GlobalTransactional, There is no global transaction , Then deduct the balance in the account module service#decrease Method to add timeout simulation .

@Override
public void decrease(Long userId, BigDecimal money) {
    
	log.info("------->account-service Start by deducting the account balance ");
	accountDao.decrease(userId, money);
	//  Simulation timeout , 30s Far exceeds the default timeout for remote calls .
	try {
    
		TimeUnit.SECONDS.sleep(30);
	} catch (InterruptedException e) {
    
		e.printStackTrace();
	}
	log.info("------->account-service The account balance is deducted from the account to end ");
}

Revisit http://localhost:2001/order/create?userId=1&productId=1&count=10&money=10
Because the deduction of account balance is timeout , Cause the deal to fail .

Let's look at db What are the data results of each module in . We can see from the following data , A new order has been added to the order Library , But the status is incomplete ( Because the deduction of balance failed ). But inventory and accounts have been successfully deducted , There is a problem of inconsistent data . It is necessary to coordinate the transaction atomicity of each branch module through distributed transactions .

6.3 Start distributed transaction reverse test

At the end of the order service#create Add a comment to the method @GlobalTransactional , To start the global transaction .

@Override
@GlobalTransactional(name = "fsp-create-order", rollbackFor = Exception.class)
public void create(Order order) {
    

	log.info("-------> Order start ");
	// This application creates orders 
	orderDao.create(order);
	// Call inventory service remotely to deduct inventory 
	log.info("------->order-service The deduction of inventory starts ");
	storageService.decrease(order.getProductId(), order.getCount());
	log.info("------->order-service After deducting the inventory from the inventory, the end ");

	// Remote call account service deduction balance 
	log.info("------->order-service The deduction balance starts ");
	accountService.decrease(order.getUserId(), order.getMoney());
	log.info("------->order-service End of deduction balance in ");

	// Change order status to completed 
	log.info("------->order-service Start by modifying the order status in ");
	orderDao.update(order.getProductId(), 0);
	log.info("------->order-service End of modifying order status in ");

	log.info("-------> End of order ");
}

After restart, the order micro service application , Revisit http://localhost:2001//order/create?userId=1&productId=1&count=10&money=10 , The transaction fails because of timeout .

But check the database table data , It's the result of last time , No new orders have been generated , There is no deduction for inventory and account balance . Because of the coordination of global transactions , When an exception occurs , The originator of the business TM( Order module ) To the transaction coordinator TC Send the message of transaction rollback , A business coordinator TC Then send rollback notification to each branch transaction , TM Roll back local transactions .

below , We go through debug Breakpoint debugging to follow up the transaction rollback process .
Breakpoint location :

Now? , Let's trigger a transaction , Jump to the breakpoint .

then , Let's check the data of the library table and their respective States . According to the position of the breakpoint , At this point, a new order should be created ( Status not complete 0), stock (70) And account balance (970) Have been deducted 10. But at this time, the global transaction has not been committed .

Because the global transaction has not been committed , Let's see seata-server Transaction related table data .
SELECT * FROM seata.global_table; In the global transaction table , A global transaction is generated XID, The originator of the business seata-order-service, Transaction groups are custom configured fsp_tx_group

SELECT * FROM seata.branch_table; In the branch transaction table , Global transaction XID Here are three branch transactions , Transactions involve resources of three modules . branch_type=AT Express seata The transaction mode of , The back can speak .

SELECT * FROM seata.lock_table; Transaction lock , You can see three business tables (t_order, t_storage, t_account) It's all locked up .

Let's take a look at the business database undo_log Table data that controls transactions .
SELECT * FROM seata_order.undo_log;

SELECT * FROM seata_storage.undo_log; overall situation XID 192.168.65.1:8091:2095810330 the .

SELECT * FROM seata_account.undo_log;

Of the above three business databases undo_log It's all recorded rollback_info data , It says db Update the previous snapshot and the updated data , It is convenient to initiate commit or rollback of global transactions . Once the global transaction initiates a commit or rollback notification , Each branch transaction will be based on rollback_info Commit or rollback local transactions with snapshot information of . After the global transaction is completed , Delete undo_log Log data .

//  Snapshot information of account table 
{
    
  "@class": "io.seata.rm.datasource.undo.BranchUndoLog",
  "xid": "192.168.65.1:8091:2095813945", //  Global transaction XID
  "branchId": 2095813953,  //  Branch business ID
  "sqlUndoLogs": [
    "java.util.ArrayList",
    [
      {
    
        "@class": "io.seata.rm.datasource.undo.SQLUndoLog",
        "sqlType": "UPDATE",
        "tableName": "t_account",
        "beforeImage": {
     //  Pre snapshot  beforeImage
          "@class": "io.seata.rm.datasource.sql.struct.TableRecords",
          "tableName": "t_account", //  Account form 
          "rows": [
            "java.util.ArrayList",
            [
              {
    
                "@class": "io.seata.rm.datasource.sql.struct.Row",
                "fields": [
                  "java.util.ArrayList",
                  [
                    {
    
                      "@class": "io.seata.rm.datasource.sql.struct.Field",
                      "name": "id",
                      "keyType": "PrimaryKey",
                      "type": -5,
                      "value": [
                        "java.lang.Long",
                        1
                      ]
                    },
                    {
    
                      "@class": "io.seata.rm.datasource.sql.struct.Field",
                      "name": "residue",  //  Balance field 
                      "keyType": "NULL",
                      "type": 3,
                      "value": [
                        "java.math.BigDecimal",
                        980  // before value 980
                      ]
                    },
                    {
    
                      "@class": "io.seata.rm.datasource.sql.struct.Field",
                      "name": "used",
                      "keyType": "NULL",
                      "type": 3,
                      "value": [
                        "java.math.BigDecimal",
                        20
                      ]
                    }
                  ]
                ]
              }
            ]
          ]
        },
        "afterImage": {
      //  Post snapshot  afterImage
          "@class": "io.seata.rm.datasource.sql.struct.TableRecords",
          "tableName": "t_account", 
          "rows": [
            "java.util.ArrayList",
            [
              {
    
                "@class": "io.seata.rm.datasource.sql.struct.Row",
                "fields": [
                  "java.util.ArrayList",
                  [
                    {
    
                      "@class": "io.seata.rm.datasource.sql.struct.Field",
                      "name": "id",
                      "keyType": "PrimaryKey",
                      "type": -5,
                      "value": [
                        "java.lang.Long",
                        1
                      ]
                    },
                    {
    
                      "@class": "io.seata.rm.datasource.sql.struct.Field",
                      "name": "residue", //  Balance field 
                      "keyType": "NULL",
                      "type": 3,
                      "value": [
                        "java.math.BigDecimal",
                        970 // after value  970
                      ]
                    },
                    {
    
                      "@class": "io.seata.rm.datasource.sql.struct.Field",
                      "name": "used",
                      "keyType": "NULL",
                      "type": 3,
                      "value": [
                        "java.math.BigDecimal",
                        30
                      ]
                    }
                  ]
                ]
              }
            ]
          ]
        }
      }
    ]
  ]
}

Let's now let go of the breakpoint , Let the program go through the process . Found that the transaction failed , The data has been rolled back , seata-server Global transaction table (global_table), Branch transaction table (branch_table), Table of transaction lock (lock_table), And for each business database undo_log The log data is deleted .

7. Add

7.1 AT Distributed transaction execution process

Look again TC/TM/RM/ Three components :

• TM Open distributed transaction , TM towards TC Register global transaction records ;
• By business scenario , Arrange the database , Services and other internal resources , RM towards TC Report resource readiness ;
• TM End distributed transaction , The end of the first phase of the business , TM notice TC Submit / Roll back distributed transactions ;
• TC Summarize transaction information , Decide whether a distributed transaction is committed or rolled back ;
• TC Inform all RM Submit / Roll back resources , The second phase of business is over .
  

7.2 AT Model details

AT Mode is how to achieve non-invasive business , There are two premises :

• Based on support for local ACID Relational database of transactions ;
• Java application , adopt JDBC Access database .

The overall mechanism of two-stage submission :

• A stage : Business data and rollback logging are committed in the same local transaction , Release local locks and connection resources .
• Two stages : (1) Submit asynchronized , It's done very quickly ; (2) Roll back , Reverse compensation through a phase of rollback log .

One stage submission ,Seata Will intercept “ Business SQL”, See the flow chart ( One stage submission )

• analysis SQL semantics , find “ Business SQL” Business data to update , Before the business data is updated , Save it as “before image”,
• perform Business SQL Update business data , After the business data is updated , Save as “after image”, Finally, a row lock is generated (lock surface ).
  All the above operations are completed in a database transaction , This ensures the atomicity of a phase operation .
  
  Two stage submission , because “ Business SQL” In one stage it has been submitted to the database , therefore Seata The framework only needs to delete the snapshot data and row lock saved in one stage , Complete the data cleaning . See the picture below ( Two stage submission )
  
  Two phase rollback ,Seata It is necessary to roll back what has been executed in one stage “ Business SQL”, Restore business data . The rollback method is to use “before image” Restore business data ; But before restoring, first check the dirty write , contrast “ Database current business data ” and “after image”, If the two data are identical, there is no dirty writing , Business data can be restored , If not, it means dirty writing , In case of dirty writing, it needs to be transferred to manual processing . See the picture below ( Two phase rollback )
  
  The underlying the aop Realization :
  

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