Transaction Management

This example demonstrates how to implement transaction management of distributed Dubbo services through Seata to ensure data consistency.

What is Seata

Seata is an open source distributed transaction solution dedicated to providing high-performance and easy-to-use distributed transaction services. Seata will provide users with AT, TCC, SAGA and XA transaction modes to create a one-stop distributed solution for users.

1. Example architecture description

The user purchases commodity business, and the whole business includes 3 microservices:

  • Inventory service: deduction of the inventory quantity of a given item.
  • Order service: Generate orders based on purchase requests.
  • Account Services: deduction of the user account amount.

image.png

StorageService

public interface StorageService {

     /**
      * Deducted storage quantity
      */
     void deduct(String commodityCode, int count);
}

OrderService

public interface OrderService {

     /**
      * Create Order
      */
     Order create(String userId, String commodityCode, int orderCount);
}

AccountService

public interface AccountService {

     /**
      * Borrow from user account
      */
     void debit(String userId, int money);
}

Two, the main business logic

BusinessService

public class BusinessServiceImpl implements BusinessService {

     private StorageService storageService;

     private OrderService orderService;

     /**
      * Purchasing
      */
     public void purchase(String userId, String commodityCode, int orderCount) {
         // Deduct storage amount
         storageService.deduct(commodityCode, orderCount);
         // Create Order
         orderService.create(userId, commodityCode, orderCount);
     }
}

StorageService

public class StorageServiceImpl implements StorageService {

     private JdbcTemplate jdbcTemplate;
  
     @Override
     public void deduct(String commodityCode, int count) {
         // Modify the database: deduct the amount of storage
         jdbcTemplate.update("update storage_tbl set count = count - ? where commodity_code = ?",
                 new Object[]{count, commodityCode});
     }
}

OrderService

public class OrderServiceImpl implements OrderService {

     private AccountService accountService;
    
     private JdbcTemplate jdbcTemplate;

     public Order create(String userId, String commodityCode, int orderCount) {
         // calculate the amount
         int orderMoney = calculate(commodityCode, orderCount);

         // The amount deducted from the user account
         accountService.debit(userId, orderMoney);

         // Modify the database: create a new order
         final Order order = new Order();
         order.userId = userId;
         order.commodityCode = commodityCode;
         order.count = orderCount;
         order.money = orderMoney;
         KeyHolder keyHolder = new GeneratedKeyHolder();
         jdbcTemplate. update(con -> {
             PreparedStatement pst = con. prepareStatement(
                     "insert into order_tbl (user_id, commodity_code, count, money) values (?, ?, ?, ?)",
                     PreparedStatement. RETURN_GENERATED_KEYS);
             pst.setObject(1, order.userId);
             pst.setObject(2, order.commodityCode);
             pst.setObject(3, order.count);
             pst.setObject(4, order.money);
             return pst;
         }, keyHolder);
         order.id = keyHolder.getKey().longValue();
         return order;
     }
}

AccountService

public class AccountServiceImpl implements AccountService {
        
     private JdbcTemplate jdbcTemplate;
    
     @Override
     public void debit(String userId, int money) {
         // Modify the database: deduct the amount from the user account
         jdbcTemplate.update("update account_tbl set money = money - ? where user_id = ?", new Object[]{money, userId});
     }
}

3. Quick start example

Step 1: Download the source code

git clone -b master https://github.com/apache/dubbo-samples.git
cd ./dubbo-samples-transaction/

Step 2: Start Seata-Server and MySQL through docker-compose

In this example, we use docker-compose to quickly pull up services like seata-server and mysql.

cd src/main/resources/docker
docker-compose up

Step 3: Build use cases

Execute the maven command to package the demo project

mvn clean package

Step 4: Start AccountService

java -classpath ./target/dubbo-samples-transaction-1.0-SNAPSHOT.jar org.apache.dubbo.samples.starter.DubboAccountServiceStarter

Step 5: Start OrderService

java -classpath ./target/dubbo-samples-transaction-1.0-SNAPSHOT.jar org.apache.dubbo.samples.starter.DubboOrderServiceStarter

Step 6: Start StorageService

java -classpath ./target/dubbo-samples-transaction-1.0-SNAPSHOT.jar org.apache.dubbo.samples.starter.DubboStorageServiceStarter

Step 7: Start BusinessService

java -classpath ./target/dubbo-samples-transaction-1.0-SNAPSHOT.jar org.apache.dubbo.samples.starter.DubboBusinessTester

4. Example core process

image.png

Step 1: Modify the business code

Here only one line of annotation @GlobalTransactional is required to be written on the method of the business initiator:

     @GlobalTransactional
     public void purchase(String userId, String commodityCode, int orderCount) {
          …
     }

Step 2: Install the database

  • Requirements: MySQL (InnoDB storage engine).

Tips: In fact, the 3 microservices in the example require 3 independent databases, but for convenience we use the same physical database and configure 3 logical connection strings.

Change the database url, username and password in the following xml files

dubbo-account-service.xml dubbo-order-service.xml dubbo-storage-service.xml

     <property name="url" value="jdbc:mysql://x.x.x.x:3306/xxx" />
     <property name="username" value="xxx" />
     <property name="password" value="xxx" />

Step 3: Create undo_log table for Seata

UNDO_LOG This table is used in Seata’s AT mode.

-- Note that when the Seata version is upgraded to 0.3.0+, the normal index will be changed to a unique index.
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;


DROP TABLE IF EXISTS `storage_tbl`;
CREATE TABLE `storage_tbl` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `commodity_code` varchar(255) DEFAULT NULL,
   `count` int(11) DEFAULT 0,
   PRIMARY KEY (`id`),
   UNIQUE KEY (`commodity_code`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


DROP TABLE IF EXISTS `order_tbl`;
CREATE TABLE `order_tbl` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `user_id` varchar(255) DEFAULT NULL,
   `commodity_code` varchar(255) DEFAULT NULL,
   `count` int(11) DEFAULT 0,
   `money` int(11) DEFAULT 0,
   PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


DROP TABLE IF EXISTS `account_tbl`;
CREATE TABLE `account_tbl` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `user_id` varchar(255) DEFAULT NULL,
   `money` int(11) DEFAULT 0,
   PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Step 5: Start the Seata-Server service

Usage: sh seata-server.sh(for linux and mac) or cmd seata-server.bat(for windows) [options]
   Options:
     --host, -h
       The host to bind.
       Default: 0.0.0.0
     --port, -p
       The port to listen.
       Default: 8091
     --storeMode, -m
       log store mode: file, db
       Default: file
     --help

e.g.

sh seata-server.sh -p 8091 -h 127.0.0.1 -m file
Last modified January 2, 2023: Enhance en docs (#1798) (95a9f4f6c1c)