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Lambda在线 > 百川分享会 > 分布式事务seata的AT模式介绍

分布式事务seata的AT模式介绍

百川分享会 2020-06-30

seata是阿里开源的一款分布式事务解决方案,致力于提供高性能和简单易用的分布式事务服务。Seata 将为用户提供了 AT、TCC、SAGA 和 XA 事务模式,本文主要介绍AT模式的使用。

seata安装

sh ./bin/seata-server.sh

支持的启动参数

参数 全写 作用 备注
-h --host 指定在注册中心注册的 IP 不指定时获取当前的 IP,外部访问部署在云环境和容器中的 server 建议指定
-p --port 指定 server 启动的端口 默认为 8091
-m --storeMode 事务日志存储方式 支持file和db,默认为 file
-n --serverNode 用于指定seata-server节点ID ,如 1,2,3..., 默认为 1
-e --seataEnv 指定 seata-server 运行环境 如 dev, test 等, 服务启动时会使用 registry-dev.conf 这样的配置

如:

sh ./bin/seata-server.sh -p 8091 -h 127.0.0.1 -m file

seata的AT模式介绍

AT模式实质是两阶段提交协议的演变,具体如下:

  • 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。

业务背景:
用户调用系统A的store服务,store服务调用系统B的company服务,company服务会新增一条数据,然后把companyId返回系统A,然后系统A通过companyId再新增一条store数据。

一般如果store服务执行失败了,直接抛异常了,所以company服务也不会执行,
但如果store服务执行成功了,已经写了一条数据到数据库,执行company服务时失败了,就会产生数据不一致的问题。

使用seata的AT模式,主要分为下面几个步骤:

  • 配置seata服务及创建事务表

  • 调用方配置(对应上面的store服务)

  • 服务提供方配置(对应上面的company服务)

配置seata服务及创建事务表

配置conf/file.conf文件

## transaction log store, only used in server side
store {
## store mode: file、db
mode = "db" //修改为db模式,标识事务信息用db存储
## file store property
file {
## store location dir
dir = "sessionStore"
# branch session size , if exceeded first try compress lockkey, still exceeded throws exceptions
maxBranchSessionSize = 16384
# globe session size , if exceeded throws exceptions
maxGlobalSessionSize = 512
# file buffer size , if exceeded allocate new buffer
fileWriteBufferCacheSize = 16384
# when recover batch read size
sessionReloadReadSize = 100
# async, sync
flushDiskMode = async
}

## database store property
db {
## the implement of javax.sql.DataSource, such as DruidDataSource(druid)/BasicDataSource(dbcp) etc.
datasource = "druid"
## mysql/oracle/postgresql/h2/oceanbase etc.
dbType = "mysql"
driverClassName = "com.mysql.cj.jdbc.Driver"
url = "jdbc:mysql://192.168.234.1:3306/seata?useUnicode=true&characterEncoding=utf8&useSSL=false&&serverTimezone=UTC" //修改数据库连接
user = "seata" //修改数据库账号
password = "123456" //修改数据库密码
minConn = 5
maxConn = 30
globalTable = "global_table"
branchTable = "branch_table"
lockTable = "lock_table"
queryLimit = 100
}
}
## server configuration, only used in server side
service {
#vgroup->rgroup
vgroup_mapping.chuanzh_tx_group = "default" //chuanzh_tx_group为自定义的事务组名称,要和客户端配置保持一致
#only support single node
default.grouplist = "192.168.234.128:8091"
#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"
}

上面配置共修改了3个地方:

  1. 存储模式改为db模式,需要创建3张事务表,如下:

    -- the table to store GlobalSession data
    CREATE TABLE IF NOT EXISTS `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`)
    ) ENGINE = InnoDB
    DEFAULT CHARSET = utf8;

    -- the table to store BranchSession data
    CREATE TABLE IF NOT EXISTS `branch_table`
    (
    `branch_id` BIGINT NOT NULL,
    `xid` VARCHAR(128) NOT NULL,
    `transaction_id` BIGINT,
    `resource_group_id` VARCHAR(32),
    `resource_id` VARCHAR(256),
    `branch_type` VARCHAR(8),
    `status` TINYINT,
    `client_id` VARCHAR(64),
    `application_data` VARCHAR(2000),
    `gmt_create` DATETIME(6),
    `gmt_modified` DATETIME(6),
    PRIMARY KEY (`branch_id`),
    KEY `idx_xid` (`xid`)
    ) ENGINE = InnoDB
    DEFAULT CHARSET = utf8;

    -- the table to store lock data
    CREATE TABLE IF NOT EXISTS `lock_table`
    (
    `row_key` VARCHAR(128) NOT NULL,
    `xid` VARCHAR(96),
    `transaction_id` BIGINT,
    `branch_id` BIGINT NOT NULL,
    `resource_id` VARCHAR(256),
    `table_name` VARCHAR(32),
    `pk` VARCHAR(36),
    `gmt_create` DATETIME,
    `gmt_modified` DATETIME,
    PRIMARY KEY (`row_key`),
    KEY `idx_branch_id` (`branch_id`)
    ) ENGINE = InnoDB
    DEFAULT CHARSET = utf8;

  2. 修改数据库连接,注意如果你安装的是MySQL8,则需要修改MySQL8的驱动:driverClassName = "com.mysql.cj.jdbc.Driver",不然会出现启动报错的问题,详细请参考:seata启动MySQL报错 #359(https://github.com/seata/seata-samples/issues/359)。

  3. 修改事务的组名,你也可以不修改,我这里使用的是:chuanzh_tx_group

  4. 创建业务事务表,记录业务需要回滚的数据,在分布式事务中,每个参与的业务数据库都需要添加对应的表

    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,
    `ext` varchar(100) DEFAULT NULL,
    PRIMARY KEY (`id`),
    UNIQUE KEY `ux_undo_log` (`xid`,`branch_id`)
    ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

配置conf/registry.conf文件

registry {
# file 、nacos 、eureka、redis、zk、consul、etcd3、sofa
type = "eureka" 修改注册方式,微服务调用使用的是Eureka

nacos {
serverAddr = "localhost"
namespace = ""
cluster = "default"
}
eureka {
serviceUrl = "http://192.168.234.1:8081/eureka" //修改Eureka地址
application = "default"
weight = "1"
}
redis {
serverAddr = "localhost:6379"
db = "0"
}
zk {
cluster = "default"
serverAddr = "127.0.0.1:2181"
session.timeout = 6000
connect.timeout = 2000
}
consul {
cluster = "default"
serverAddr = "127.0.0.1:8500"
}
etcd3 {
cluster = "default"
serverAddr = "http://localhost:2379"
}
sofa {
serverAddr = "127.0.0.1:9603"
application = "default"
region = "DEFAULT_ZONE"
datacenter = "DefaultDataCenter"
cluster = "default"
group = "SEATA_GROUP"
addressWaitTime = "3000"
}
file {
name = "file.conf"
}
}

调用方配置(store-server)

maven配置,使用seata-spring-boot-starter,自动配置的方式,不需要再添加file.conf和register.conf文件

    <!--druid-->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid-spring-boot-starter</artifactId>
<version>${druid-spring-boot-starter.version}</version>
</dependency>

<!--seata-->
<dependency>
<groupId>io.seata</groupId>
<artifactId>seata-spring-boot-starter</artifactId>
<version>1.2.0</version>
</dependency>

application.properties配置:

server.port=9090
spring.application.name=store-server

mybatis.type-aliases-package=com.chuanzh.model
mybatis.mapper-locations=classpath:mapper/*.xml

spring.datasource.url=jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8
spring.datasource.username=root
spring.datasource.password=123456
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

#注意这里的事务组配置要和服务端一致
seata.tx-service-group=chuanzh_tx_group
seata.service.vgroup-mapping.chuanzh_tx_group=default
seata.service.grouplist.default=192.168.234.128:8091

logging.level.io.seata=DEBUG
## eureka
eureka.client.serviceUrl.defaultZone= http://localhost:8081/eureka/

数据源配置,因为seata是对数据库的datasource进行了接管和代理,所以在每个参与分布式事务的数据源都要进行如下配置:

@Configuration
public class DataSourceConfiguration {

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

@Primary
@Bean("dataSource")
public DataSourceProxy dataSource(DataSource druidDataSource){
return new DataSourceProxy(druidDataSource);
}

@Bean
public SqlSessionFactory sqlSessionFactory(DataSourceProxy dataSourceProxy)throws Exception{
SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
sqlSessionFactoryBean.setDataSource(dataSourceProxy);
sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver()
.getResources("classpath*:/mapper/*.xml"));
sqlSessionFactoryBean.setTransactionFactory(new SpringManagedTransactionFactory());
return sqlSessionFactoryBean.getObject();
}

}

注意配置了数据源后,启动会出现循环依赖的问题,如下,

还需要在启动类排除dataSource自动配置,其它的解决方法,可以参考:集成fescar数据源循环依赖错误解决方案(https://blog.csdn.net/kangsa998/article/details/90042406)

@SpringBootApplication(exclude = DataSourceAutoConfiguration.class)

配置请求拦截器,生成一个请求事务ID,用于在微服务中传递

@Configuration
public class SeataRequestInterceptor implements RequestInterceptor {
@Override
public void apply(RequestTemplate requestTemplate) {
String xid = RootContext.getXID();
if (StringUtils.isNotBlank(xid)) {
//构建请求头
requestTemplate.header("TX_XID", xid);
}
}
}

服务提供方配置(company-server)

maven、application.properties、数据源配置同调用方配置,区别主要是拦截器的配置,如下:

@Slf4j
@Component
public class SeataHandlerInterceptor implements HandlerInterceptor {

public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
String xid = RootContext.getXID();
String rpcXid = request.getHeader("TX_XID");
//获取全局事务编号
if(log.isDebugEnabled()) {
log.debug("xid in RootContext {} xid in RpcContext {}", xid, rpcXid);
}
if(xid == null && rpcXid != null) {
//设置全局事务编号
RootContext.bind(rpcXid);
if(log.isDebugEnabled()) {
log.debug("bind {} to RootContext", rpcXid);
}
}
return true;
}
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception e) {
String rpcXid = request.getHeader("TX_XID");
if(!StringUtils.isEmpty(rpcXid)) {
String unbindXid = RootContext.unbind();
if(log.isDebugEnabled()) {
log.debug("unbind {} from RootContext", unbindXid);
}

if(!rpcXid.equalsIgnoreCase(unbindXid)) {
log.warn("xid in change during RPC from {} to {}", rpcXid, unbindXid);
if(unbindXid != null) {
RootContext.bind(unbindXid);
log.warn("bind {} back to RootContext", unbindXid);
}
}

}
}

}
@Configuration
public class WebMvcConfiguration implements WebMvcConfigurer {

@Autowired
private SeataHandlerInterceptor seataHandlerInterceptor;

public void addInterceptors(InterceptorRegistry registry) {
//注册HandlerInterceptor,拦截所有请求
registry.addInterceptor(seataHandlerInterceptor).addPathPatterns(new String[]{"/**"});
}

}

添加全局事务注解

在服务调用方的方法上添加@GlobalTransactional注解,下面模拟了一种场景,如果companyId为偶数,则会抛异常。

    @GlobalTransactional(rollbackFor = Exception.class)
public void create(StoreEntity storeEntity) throws Exception {
CompanyEntity companyEntity = new CompanyEntity();
companyEntity.setName(storeEntity.getName());
companyEntity = companyFeign.createCompany(companyEntity);

/**
* 模拟异常
*/
if (companyEntity.getId() % 2 == 0) {
throw new Exception();
}

/** 写入store数据 */
storeEntity.setCompanyId(companyEntity.getId());
storeMapper.insert(storeEntity);
}

经过测试,companyFeign.createCompany服务调用后会先向数据库写一条数据,当create方法执行抛异常,就会事务回滚,删除掉原先的company数据


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