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Seata Transaction

Background

Apache ShardingSphere provides BASE transactions that integrate the Seata implementation. All references to Seata integration in this article refer to Seata AT mode.

Prerequisites

Introduce Maven dependencies and exclude the outdated Maven dependencies of org.antlr:antlr4-runtime:4.8 in io.seata:seata-all.

<project>
    <dependencies>
      <dependency>
         <groupId>org.apache.shardingsphere</groupId>
         <artifactId>shardingsphere-jdbc</artifactId>
         <version>${shardingsphere.version}</version>
      </dependency>
      <dependency>
         <groupId>org.apache.shardingsphere</groupId>
         <artifactId>shardingsphere-transaction-base-seata-at</artifactId>
         <version>${shardingsphere.version}</version>
      </dependency>
      <dependency>
         <groupId>io.seata</groupId>
         <artifactId>seata-all</artifactId>
         <version>2.0.0</version>
         <exclusions>
            <exclusion>
               <groupId>org.antlr</groupId>
               <artifactId>antlr4-runtime</artifactId>
            </exclusion>
         </exclusions>
      </dependency>
    </dependencies>
</project>

Procedure

  1. Start Seata Server
  2. Create the log table
  3. Add the Seata configuration

Sample

Start Seata Server

Follow the steps in seata-fescar-workshop or https://hub.docker.com/r/seataio/seata-server , download and start the Seata server.

Create undo_log table

Create the undo_log table in each shard database instance (take MySQL as an example). The content of SQL is subject to the corresponding database in https://github.com/apache/incubator-seata/tree/v2.0.0/script/client/at/db .

CREATE TABLE IF NOT EXISTS `undo_log`
(
   `branch_id`     BIGINT       NOT NULL COMMENT 'branch transaction id',
   `xid`           VARCHAR(128) NOT NULL COMMENT 'global transaction id',
   `context`       VARCHAR(128) NOT NULL COMMENT 'undo_log context,such as serialization',
   `rollback_info` LONGBLOB     NOT NULL COMMENT 'rollback info',
   `log_status`    INT(11)      NOT NULL COMMENT '0:normal status,1:defense status',
   `log_created`   DATETIME(6)  NOT NULL COMMENT 'create datetime',
   `log_modified`  DATETIME(6)  NOT NULL COMMENT 'modify datetime',
   UNIQUE KEY `ux_undo_log` (`xid`, `branch_id`)
   ) ENGINE = InnoDB AUTO_INCREMENT = 1 DEFAULT CHARSET = utf8mb4 COMMENT ='AT transaction mode undo table';

ALTER TABLE `undo_log` ADD INDEX `ix_log_created` (`log_created`);

Modify configuration

Add the seata.conf file to the root directory of the classpath. The configuration file format refers to the JavaDoc of io.seata.config.FileConfiguration.

There are four properties in seata.conf,

  1. shardingsphere.transaction.seata.at.enable, when this value is true, ShardingSphere’s Seata AT integration is enabled, there is a default value of true
  2. shardingsphere.transaction.seata.tx.timeout, global transaction timeout in SECONDS, there is a default value of 60
  3. client.application.id, apply the only primary key
  4. client.transaction.service.group, the transaction group it belongs to, there is a default value of default

A fully configured seata.conf is as follows,

shardingsphere.transaction.seata.at.enable = true
shardingsphere.transaction.seata.tx.timeout = 60

client {
    application.id = example
    transaction.service.group = default_tx_group
}

Modify the registry.conf file of Seata as required.

Usage restrictions

ShardingSphere’s Seata integration does not support isolation levels.

ShardingSphere’s Seata integration places the obtained Seata global transaction into the thread’s local variables. And org.apache.seata.spring.annotation.GlobalTransactionScanner uses Dynamic Proxy to enhance the method. This means that users should never use the io.seata:seata-all Java annotation for ShardingSphere’s DataSource. That is, when using ShardingSphere’s Seata integration, users should avoid using the Java API of io.seata:seata-all.

For ShardingSphere data source, discuss 6 situations,

  1. Manually obtain the java.sql.Connection instance created from the ShardingSphere data source, and manually calling the setAutoCommit(), commit() and rollback() methods is allowed.

  2. Using the Jakarta EE 8 javax.transaction.Transactional annotation on the function is allowed.

  3. Using Jakarta EE 9/10’s jakarta.transaction.Transactional annotation on functions is allowed.

  4. Using Spring Framework’s org.springframework.transaction.annotation.Transactional annotation on functions is allowed.

  5. Using the io.seata.spring.annotation.GlobalTransactional annotation on the function is not allowed.

  6. Manually create io.seata.tm.api.GlobalTransaction instance from io.seata.tm.api.GlobalTransactionContext, calling the begin(), commit() and rollback() methods of an io.seata.tm.api.GlobalTransaction instance is not allowed.

For Seata Server 2.0.0, Seata Server does not pass the return value of io.seata.core.context.RootContext.getXID() to all connected Seata Client instances of the same transaction group, Reference https://seata.apache.org/docs/user/api/ . This requires discussing two situations,

  1. In the scenario of using ShardingSphere JDBC, transaction scenarios across multiple microservices need to consider using io.seata.core.context.RootContext.getXID() in the context of the starting microservice to obtain the Seata XID and then pass it to the ending microservice through RPC, and call io.seata.core.context.RootContext.bind(rpcXid) in the business function of the endpoint microservice.

  2. In the scenario of using ShardingSphere Proxy, Multiple microservices operate local transactions against the logical dataSource of ShardingSphere Proxy, this will be converted into distributed transaction operations on the server side of ShardingSphere Proxy, there are no additional Seata XIDs to consider.

In the actual scenario of using Spring Boot OSS, com.alibaba.cloud:spring-cloud-starter-alibaba-seata and io.seata:seata-spring-boot-starter are often introduced transitively by other Maven dependencies. In order to avoid transaction conflicts, users need to manually turn off Seata’s auto-config class. And set the seata.enable-auto-data-source-proxy property to false in the Spring Boot OSS configuration file. A possible dependency is as follows.

<project>
     <dependencies>
       <dependency>
          <groupId>org.apache.shardingsphere</groupId>
          <artifactId>shardingsphere-jdbc</artifactId>
          <version>${shardingsphere.version}</version>
       </dependency>
       <dependency>
          <groupId>org.apache.shardingsphere</groupId>
          <artifactId>shardingsphere-transaction-base-seata-at</artifactId>
          <version>${shardingsphere.version}</version>
       </dependency>
       <dependency>
          <groupId>io.seata</groupId>
          <artifactId>seata-spring-boot-starter</artifactId>
          <version>2.0.0</version>
          <exclusions>
             <exclusion>
                <groupId>org.antlr</groupId>
                <artifactId>antlr4-runtime</artifactId>
             </exclusion>
          </exclusions>
       </dependency>
     </dependencies>
</project>

The corresponding Spring Boot OSS bootstrap class may be as follows.

import io.seata.spring.boot.autoconfigure.SeataAutoConfiguration;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication(exclude = SeataAutoConfiguration.class)
public class ExampleApplication {

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

}

The corresponding application.yml under the classpath needs to contain the following configuration. In this case, the equivalent configuration of Seata’s registry.conf defined in application.yaml of Spring Boot OSS may not be valid. This depends on the Seata Client. When a downstream project uses the Maven module org.apache.shardingsphere:shardingsphere-transaction-base-seata-at, users are always encouraged to configure Seata Client using registry.conf.

seata:
   enable-auto-data-source-proxy: false