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    How to use Seata to ensure consistency between Dubbo Microservices

    This article will introduce you how to use Seata to ensure consistency between Dubbo Microservices.

    Use case

    A business logic for user purchasing commodities. The whole business logic is powered by 3 microservices:

    • Storage service: deduct storage count on given commodity.
    • Order service: create order according to purchase request.
    • Account service: debit the balance of user’s account.

    Architecture

    Architecture

    StorageService

    public interface StorageService {

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

    OrderService

    public interface OrderService {

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

    AccountService

    public interface AccountService {

    /**
     * debit balance of user's account
     */
    void debit(String userId, int money);
}

    Main business logic

    public class BusinessServiceImpl implements BusinessService {

    private StorageService storageService;

    private OrderService orderService;

    /**
     * purchase
     */
    public void purchase(String userId, String commodityCode, int orderCount) {

        storageService.deduct(commodityCode, orderCount);

        orderService.create(userId, commodityCode, orderCount);
    }
}

    public class StorageServiceImpl implements StorageService {

  private StorageDAO storageDAO;
  
    @Override
    public void deduct(String commodityCode, int count) {
        Storage storage = new Storage();
        storage.setCount(count);
        storage.setCommodityCode(commodityCode);
        storageDAO.update(storage);
    }
}

    public class OrderServiceImpl implements OrderService {

    private OrderDAO orderDAO;

    private AccountService accountService;

    public Order create(String userId, String commodityCode, int orderCount) {

        int orderMoney = calculate(commodityCode, orderCount);

        accountService.debit(userId, orderMoney);

        Order order = new Order();
        order.userId = userId;
        order.commodityCode = commodityCode;
        order.count = orderCount;
        order.money = orderMoney;

        return orderDAO.insert(order);
    }
}

    Distributed Transaction Solution with Seata

    undefined

    We just need an annotation @GlobalTransactional on business method:

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

    Example powered by Dubbo + Seata

    Step 1: Setup database

    • Requirement: MySQL with InnoDB engine.

    Note: In fact, there should be 3 database for the 3 services in the example use case. However, we can just create one database and configure 3 data sources for simple.

    Modify Spring XML with the database URL/username/password you just created.

    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 2: Create undo_log table for Seata

    UNDO_LOG table is required by Seata AT mode.

    -- Note that when Seata version is upgraded to 0.3.0+, it is changed from the previous normal index to the 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;

    Step 3: Create tables for example business

    
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 4: Start Seata-Server

    • Download server package, unzip it.
    • Start Seata-Server
    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

    Step 5: Run example