一、简介

官网地址: http://seata.io/zh-cn/

1，概念

Seata是一款开源的分布式事务解决方案，致力于在微服务架构在提供高性能和简单一样的分布式事务服务。

2，处理过程

Transaction ID XID:全局唯一的事务ID

Transaction Coordinator(TC) :维护全局和分支事务的状态，驱动全局事务提交或回滚。

Transaction Manager™ :定义全局事务的范围：开始全局事务、提交或回滚全局事务。

Resource Manager(RM) :管理分支事务处理的资源，与TC交谈以注册分支事务和报告分支事务的状态，并驱动分支事务提交或回滚。

• TM向TC申请开启一个全局事务，全局事务创建成功并生成一个全局唯一的XID
• XID在微服务调用链路的上下文中传播
• RM向TC注册分支事务，将其纳入XID对应全局事务的管辖
• TM向TC发起针对XID的全局提交或回滚决议
• TC调度XID下管辖的全部分支事务完成提交或回滚请求

二、Seata-Server的安装

1，下载

http://seata.io/zh-cn/blog/download.html 选择指定版本下载(我这里用的是0.9.0)

2，修改配置文件

修改seata/conf/file.conf

#将service中修改groupvgroup_mapping.my_test_tx_group = "my_group"#将store模块修改为db并修改数据连接，将conf目录下的db_store.sql文件导入到数据库中mode = "db"db { datasource = "dbcp" db-type = "mysql" driver-class-name = "com.mysql.jdbc.Driver" url = "jdbc:mysql://127.0.0.1:3306/seata" user = "root" password = "123456"}

修改seata/conf/registry.conf

registry { type = "nacos" nacos { serverAddr = "localhost:8848" namespace = "" cluster = "default" }

三、Seata的应用

1，订单服务

源码: seata-order-service2001

a，配置pom

<!--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>

b，配置yaml

server: port: 2001spring: application: name: seata-order-service cloud: alibaba: seata: #自定义事务组名称需要与seata-server中的对应 tx-service-group: my_group nacos: discovery: server-addr: localhost:8848 datasource: driver-class-name: com.mysql.jdbc.Driver url: jdbc:mysql://localhost:3306/seata_order username: root password: 123456feign: hystrix: enabled: falselogging: level: io: seata: infomybatis: mapperLocations: classpath:mapper/*.xml

c，添加file.conf(与seata-server配置相同)

transport { # tcp udt unix-domain-socket type = "TCP" #NIO NATIVE server = "NIO" #enable heartbeat heartbeat = true #thread factory for netty thread-factory { boss-thread-prefix = "NettyBoss" worker-thread-prefix = "NettyServerNIOWorker" server-executor-thread-prefix = "NettyServerBizHandler" share-boss-worker = false client-selector-thread-prefix = "NettyClientSelector" client-selector-thread-size = 1 client-worker-thread-prefix = "NettyClientWorkerThread" # netty boss thread size,will not be used for UDT boss-thread-size = 1 #auto default pin or 8 worker-thread-size = 8 } shutdown { # when destroy server, wait seconds wait = 3 } serialization = "seata" compressor = "none"}service { vgroup_mapping.my_group = "default" default.grouplist = "127.0.0.1:8091" enableDegrade = false disable = false max.commit.retry.timeout = "-1" max.rollback.retry.timeout = "-1" disableGlobalTransaction = false}client { async.commit.buffer.limit = 10000 lock { retry.internal = 10 retry.times = 30 } report.retry.count = 5 tm.commit.retry.count = 1 tm.rollback.retry.count = 1}## transaction log storestore { ## store mode: file、db 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 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 = "123456" min-conn = 1 max-conn = 3 global.table = "global_table" branch.table = "branch_table" lock-table = "lock_table" query-limit = 100 }}lock { ## the lock store mode: local、remote mode = "remote" local { ## store locks in user's database } remote { ## store locks in the seata's server }}recovery { #schedule committing retry period in milliseconds committing-retry-period = 1000 #schedule asyn committing retry period in milliseconds asyn-committing-retry-period = 1000 #schedule rollbacking retry period in milliseconds rollbacking-retry-period = 1000 #schedule timeout retry period in milliseconds timeout-retry-period = 1000}transaction { undo.data.validation = true undo.log.serialization = "jackson" undo.log.save.days = 7 #schedule delete expired undo_log in milliseconds undo.log.delete.period = 86400000 undo.log.table = "undo_log"}## metrics settingsmetrics { enabled = false registry-type = "compact" # multi exporters use comma divided exporter-list = "prometheus" exporter-prometheus-port = 9898}support { ## spring spring { # auto proxy the DataSource bean datasource.autoproxy = false }}

d，添加registry.conf(与seata-server的配置相同)

registry { # file 、nacos 、eureka、redis、zk、consul、etcd3、sofa type = "nacos" nacos { serverAddr = "localhost:8848" namespace = "" cluster = "default" } eureka { serviceUrl = "http://localhost:8761/eureka" 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" }}config { # file、nacos 、apollo、zk、consul、etcd3 type = "file" nacos { serverAddr = "localhost" namespace = "" } consul { serverAddr = "127.0.0.1:8500" } apollo { app.id = "seata-server" apollo.meta = "http://192.168.1.204:8801" } zk { serverAddr = "127.0.0.1:2181" session.timeout = 6000 connect.timeout = 2000 } etcd3 { serverAddr = "http://localhost:2379" } file { name = "file.conf" }}

e，fegin调用(这里以其中一个account为例)

@FeignClient(value = "seata-account-service")public interface AccountService { @RequestMapping("/account/decrease") public CommonResult decrease(@RequestParam("userId") Long userId, @RequestParam("money") BigDecimal money);}

f，事务service

@Slf4j@Servicepublic class OrderServiceImpl implements OrderService { @Autowired OrderDao orderDao; @Autowired AccountService accountService; @Autowired StorageService storageService; @Override @GlobalTransactional(name = "my-order-test",rollbackFor = Exception.class) //加注解使用全局的事务，name 为事务名称不重复就行 public Long create(Order order) { log.info("=========================下订单，开始"); orderDao.create(order); log.info("=========================下订单，完成"); log.info("=========================减库存，开始"); storageService.decrease(order.getProductId(), order.getCount()); log.info("=========================减库存，完成"); log.info("=========================减积分，开始"); accountService.decrease(order.getUserId(), order.getMoney()); log.info("=========================减积分，完成"); log.info("=========================订单状态修改，开始"); orderDao.update(order.getId(),1); log.info("=========================订单状态修改，完成"); return order.getId(); }}

g，启动类

2，库存服务

源码： seata-storage-service2002

与订单服务中的a，b，c，d，g配置步骤相同

3，账户服务

源码: seata-account-service2003

与库存服务的配置步骤相同

四、Seata的原理解析

参考文档： http://seata.io/zh-cn/docs/overview/what-is-seata.html

1，AT模式一阶段

1，解析SQL语义，找到"业务SQL"要更新的业务数据，在业务数据被更新前，将其保存成"before image"
2，执行"业务SQL"更新业务数据，在业务数更新之后
3，将其保存成"after image"，最后生成行锁。
以上操作全部在一个数据库事务内完成，这样保证了一阶段操作的原子性。

二阶段提交

因为"业务SQL"在一阶段已经提交至数据库，所以seata框架只需将一阶段保存的快照数据和行锁删掉，完成数据清理即可。

二阶段回滚

二阶段如果是回滚的话，seata就需要回滚一阶段已经执行的"业务SQL"，还原业务数据。

回滚的方式便是用"before image"还原业务数据；但在还原前要首先校验脏写，对比"数据库当前业务数据"和"after image"

如果两份数据完全一致就说明没有脏写，可以还原业务数据，如果不一致就说明有脏写，出现脏写就需要转人工处理。

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