AT模式是 Seata 主推的分布式事务解决方案,它使得应用代码可以像使用本地事物一样使用分布式事物，完全屏蔽了底层细节，主要有以下几点：
- AT模式依赖全局事物注解和代理数据源，其余代码不需要变更，对业务无侵入、接入成本低；
- AT模式的作用范围在于底层数据，通过保存操作行记录的前后快照和生成反向SQL语句进行补偿操作，对上层应用透明；
- AT模式需借助全局锁和GlobalLock注解来解决全局事务间的写冲突问题，如果一阶段分支事物成功则二阶段一开始全局锁即被释放，否则需要等到分支事务二阶段回滚完成才能释放全局锁；
概括来讲，AT 模式的工作流程分为两阶段。一阶段进行业务 SQL 执行，并通过 SQL 拦截、SQL 改写等过程生成修改数据前后的快照（Image），并作为 UndoLog 和业务修改在同一个本地事务中提交。
如果一阶段成功那么二阶段仅仅异步删除刚刚插入的 UndoLog；如果二阶段失败则通过 UndoLog 生成反向 SQL 语句回滚一阶段的数据修改。
<!--seata组件包-->
<dependency>
<groupId>io.seata</groupId>
<artifactId>seata-all</artifactId>
<version>${seata.version}</version>
</dependency>
<!--spring cloud 相关定制-->
<dependency>
<groupId>com.alibaba.cloud</groupId>
<artifactId>spring-cloud-alibaba-seata</artifactId>
<version>x.y.z</version>
</dependency>注意：seata兼容版本说明
registry.conf配置文件，euraka中的application是指seata的服务端的服务器，这边要注意seata server有事物分组的概念，用于不同业务方的集群分区。
registry {
# 注册中心支持file 、nacos 、eureka、redis、zk,推荐eureka做负载均衡
type = "eureka"
eureka {
serviceUrl = "http://192.168.202.137:8761/eureka"
# seata server注册中心的服务名
application = "seata-server-default-group"
weight = "1"
}
}
config {
# 配置中心支持file、nacos 、apollo、zk,推荐apollo
type = "file"
file {
name = "file.conf"
}
}
file.conf配置文件，这里需要注意service中的vgroup_mapping配置，其中vgroup_mapping.my_test_tx_group的my_test_tx_group是表示逻辑服务分组，值表示seata server的实际服务分组，一定要存在seata serve的分组名
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->rgroup
vgroup_mapping.my_test_tx_group = "seata-server-default-group"
#only support single node
default.grouplist = "127.0.0.1:8091"
#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"
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 {
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"
}
support {
## spring
spring {
# auto proxy the DataSource bean
datasource.autoproxy = false
}
}
application.yml配置文件
spring:
cloud:
alibaba:
seata:
## 该服务分组名一定要和file.conf配置文件中的service.vgroup_mapping一致，不然找不到对应的seata server集群名
tx-service-group: my_test_tx_group配置代理数据源(DataSourceProxy)即可.
@Configuration
@MapperScan("com.fly.seata.dao")
public class DatasourceAutoConfig {
@Bean
@ConfigurationProperties(prefix = "spring.datasource")
public DataSource druidDataSource(){
DruidDataSource druidDataSource = new DruidDataSource();
return druidDataSource;
}
@Bean("dataSourceProxy")
public DataSourceProxy dataSourceProxy(DataSource druidDataSource){
return new DataSourceProxy(druidDataSource);
}
@Bean
public SqlSessionFactory sqlSessionFactory(DataSourceProxy dataSourceProxy)throws Exception{
SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
sqlSessionFactoryBean.setDataSource(dataSourceProxy);
sqlSessionFactoryBean.setTransactionFactory(new SpringManagedTransactionFactory());
return sqlSessionFactoryBean.getObject();
}
}@RestController
public class TmController {
@Autowired
private OrderApi orderApi;
@Autowired
private StorageApi storageApi;
@GlobalLock
@GlobalTransactional
@GetMapping("/tm/purchase")
public String purchase(){
OrderDTO order = new OrderDTO();
order.setProductId(1l);
order.setCount(1);
order.setMoney(new BigDecimal(1));
order.setUserId(1l);
orderApi.createOrder(order);
storageApi.reduce(order.getProductId(),order.getCount());
return "ok";
}
}TM端启动日志发现注册成功的日志，即可说明配置成功！
2019-11-14 16:55:33.302 INFO 5420 --- [imeoutChecker_1] i.s.c.r.netty.NettyClientChannelManager : will connect to 192.168.202.149:8091
2019-11-14 16:55:33.304 INFO 5420 --- [imeoutChecker_1] i.s.core.rpc.netty.NettyPoolableFactory : NettyPool create channel to transactionRole:TMROLE,address:192.168.202.149:8091,msg:< RegisterTMRequest{applicationId='seata-at-rm-one', transactionServiceGroup='my_test_tx_group'} >
2019-11-14 16:55:33.320 INFO 5420 --- [imeoutChecker_1] i.s.core.rpc.netty.NettyPoolableFactory : register success, cost 11 ms, version:0.9.0,role:TMROLE,channel:[id: 0xd6e6cdde, L:/192.168.202.149:53471 - R:/192.168.202.149:8091]
测试Demo成功日志如下
TM端日志：
2019-11-14 17:18:34.841 INFO 5478 --- [nio-8080-exec-7] i.seata.tm.api.DefaultGlobalTransaction : Begin new global transaction [192.168.202.149:8091:2027442865]
2019-11-14 17:18:35.234 INFO 5478 --- [nio-8080-exec-7] i.seata.tm.api.DefaultGlobalTransaction : [192.168.202.149:8091:2027442865] commit status:Committed
RM端日志：
2019-11-14 17:18:35.642 INFO 5472 --- [atch_RMROLE_3_8] i.s.core.rpc.netty.RmMessageListener : onMessage:xid=192.168.202.149:8091:2027442865,branchId=2027442870,branchType=AT,resourceId=jdbc:mysql://127.0.0.1:3306/seata-storage,applicationData=null
2019-11-14 17:18:35.642 INFO 5472 --- [atch_RMROLE_3_8] io.seata.rm.AbstractRMHandler : Branch committing: 192.168.202.149:8091:2027442865 2027442870 jdbc:mysql://127.0.0.1:3306/seata-storage null
2019-11-14 17:18:35.642 INFO 5472 --- [atch_RMROLE_3_8] io.seata.rm.AbstractRMHandler : Branch commit result: PhaseTwo_Committed
2019-11-14 17:18:42.510 INFO 5472 --- [trap-executor-0] c.n.d.s.r.aws.ConfigClusterResolver : Resolving eureka endpoints via configuration
2019-11-14 17:18:44.733 INFO 5472 --- [trap-executor-0] c.n.d.s.r.aws.ConfigClusterResolver : Resolving eureka endpoints via configuration
TC端日志：
2019-11-14 17:18:34.828 INFO [batchLoggerPrint_1]io.seata.core.rpc.DefaultServerMessageListenerImpl.run:198 -SeataMergeMessage timeout=60000,transactionName=purchase()
,clientIp:192.168.202.149,vgroup:my_test_tx_group
2019-11-14 17:18:34.838 INFO [ServerHandlerThread_66_500]io.seata.server.coordinator.DefaultCore.begin:145 -Successfully begin global transaction xid = 192.168.202.149:8091:2027442865
2019-11-14 17:18:34.868 INFO [batchLoggerPrint_1]io.seata.core.rpc.DefaultServerMessageListenerImpl.run:198 -SeataMergeMessage xid=192.168.202.149:8091:2027442865,branchType=AT,resourceId=jdbc:mysql://127.0.0.1:3306/seata-order,lockKey=`order`:59
,clientIp:192.168.202.149,vgroup:my_test_tx_group
2019-11-14 17:18:34.912 INFO [ServerHandlerThread_67_500]io.seata.server.coordinator.DefaultCore.lambda$branchRegister$0:94 -Successfully register branch xid = 192.168.202.149:8091:2027442865, branchId = 2027442867
2019-11-14 17:18:34.951 INFO [batchLoggerPrint_1]io.seata.core.rpc.DefaultServerMessageListenerImpl.run:198 -SeataMergeMessage xid=192.168.202.149:8091:2027442865,branchId=2027442867,resourceId=null,status=PhaseOne_Done,applicationData=null
,clientIp:192.168.202.149,vgroup:my_test_tx_group
2019-11-14 17:18:34.970 INFO [ServerHandlerThread_68_500]io.seata.server.coordinator.DefaultCore.branchReport:118 -Successfully branch report xid = 192.168.202.149:8091:2027442865, branchId = 2027442867
2019-11-14 17:18:35.011 INFO [batchLoggerPrint_1]io.seata.core.rpc.DefaultServerMessageListenerImpl.run:198 -SeataMergeMessage xid=192.168.202.149:8091:2027442865,branchType=AT,resourceId=jdbc:mysql://127.0.0.1:3306/seata-storage,lockKey=storage:1
,clientIp:192.168.202.149,vgroup:my_test_tx_group
2019-11-14 17:18:35.063 INFO [ServerHandlerThread_69_500]io.seata.server.coordinator.DefaultCore.lambda$branchRegister$0:94 -Successfully register branch xid = 192.168.202.149:8091:2027442865, branchId = 2027442870
2019-11-14 17:18:35.112 INFO [batchLoggerPrint_1]io.seata.core.rpc.DefaultServerMessageListenerImpl.run:198 -SeataMergeMessage xid=192.168.202.149:8091:2027442865,branchId=2027442870,resourceId=null,status=PhaseOne_Done,applicationData=null
,clientIp:192.168.202.149,vgroup:my_test_tx_group
2019-11-14 17:18:35.158 INFO [ServerHandlerThread_70_500]io.seata.server.coordinator.DefaultCore.branchReport:118 -Successfully branch report xid = 192.168.202.149:8091:2027442865, branchId = 2027442870
2019-11-14 17:18:35.170 INFO [batchLoggerPrint_1]io.seata.core.rpc.DefaultServerMessageListenerImpl.run:198 -SeataMergeMessage xid=192.168.202.149:8091:2027442865,extraData=null
,clientIp:192.168.202.149,vgroup:my_test_tx_group
2019-11-14 17:18:35.660 INFO [AsyncCommitting_1]io.seata.server.coordinator.DefaultCore.doGlobalCommit:303 -Global[192.168.202.149:8091:2027442865] committing is successfully done.