分布式事务解决方案--Seata--实操

• Seata
• 背景介绍
• Seata版本选择
• Seata实操
• 1.问题描述
• 2.问题定位
• 3.解决方案

Seata

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下提供高性能和简单易用的分布式事务服务。
本文旨在使用Seata进行开发过程中踩过的坑进行记录与总结，不对Seata原理介绍，有兴趣可参考官方文档。

背景介绍

在应用分布式架构的时候，不可不免的会遇到分布式事务的问题，市面上有很多成熟的解决方案，本次选用阿里巴巴开源的Seata作为分布式事务的解决方案，主要是因为阿里现在致力于打造分布式的阿里生态环境，而SpringCloud中很多组件都已经停更，而阿里开源的一系列组件都更稳定且持续更新，所以选择阿里系。

Seata版本选择

Seata目前最新版本是1.20（2020-04-20），本次开发使用的Seata版本为1.10（2020-02-19），这里也是怕最新版本不稳定。
附Seata下载地址：
链接: http://seata.io/zh-cn/blog/download.html.

Seata实操

在使用Seata进行开发的时候遇到了一些问题，做一些记录与总结

1.问题描述

按照官方文档进行安装与配置，将三个微服务注册在同一全局事务组下，名为fsp_tx_group，Seata服务端与微服务都正常启动，但是却出现了全局事务回滚失败的问题，具体问题如下：
逻辑业务为：微服务A写入数据库A，然后调用微服务B写入数据库B，最后调用微服务C写入数据库C，这三个微服务的调用组成一次全局事务，若中间任何一个环节出错，那么数据库A、B、C都要回滚，但是按照文档配置都正确后，发现数据库C始终回滚失败，即数据库A与B都回滚了，但是数据库C的更改依然保留，并未回滚。

2.问题定位

经排查，代码和配置文件并未出错，但是在Seata服务端的启动日志里发现一些端倪，如下图：

大图如下：

RM（Resource Manager）注册的地址出现问题，下面两个微服务可以注册到Mysql的数据库，但是最上面的RM未注册到Mysql数据库中，RM为Seata三大组件中的一个，组件及原理参见官方文档。
但为什么注册不到数据库，就没办法回滚了呢？因为数据库中有一张名为undo_log的表，这张表记录着数据更改之前的快照，全局事务ID等信息，所以当RM连接不到数据库时，无法将这些信息记录到undo_log这张表里，即导致回滚失败。
undo_log这张表是官方文档中给出的，在建立开发环境时配好。

3.解决方案

至于为什么RM连接数据库的时候会出错，经过分析后，发现application.yml文件中的数据库映射并没有配置错误，数据库也正常，但就是注册不成功，
所以尝试以下三种解决方案：
1.删除数据库，重新建库建表，经验证，未解决问题。
2.重新写Seata客户端的file.conf配置文件，经验证，未解决问题。
3.删除IDE整个module，重新建立module，拷贝同样的代码与配置文件，经验证，问题解决。
下面附上Seata配置文件与application.yml

file.conf:

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
  vgroupMapping.fsp_tx_group = "default"
  #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 log store
store {
  ## 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 = "phoenix1991mh"
    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 settings
metrics {
  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
  }
}

registry.conf:

registry {
  # file 、nacos 、eureka、redis、zk
  type = "nacos"

  nacos {
    serverAddr = "localhost:8848"
    namespace = ""
    cluster = "default"
  }
  eureka {
    serviceUrl = "http://localhost:8761/eureka"
    application = "default"
    weight = "1"
  }
  redis {
    serverAddr = "localhost:6381"
    db = "0"
  }
  zk {
    cluster = "default"
    serverAddr = "127.0.0.1:2181"
    session.timeout = 6000
    connect.timeout = 2000
  }
  file {
    name = "file.conf"
  }
}

config {
  # file、nacos 、apollo、zk
  type = "file"

  nacos {
    serverAddr = "localhost"
    namespace = ""
    cluster = "default"
  }
  apollo {
    app.id = "fescar-server"
    apollo.meta = "http://192.168.1.204:8801"
  }
  zk {
    serverAddr = "127.0.0.1:2181"
    session.timeout = 6000
    connect.timeout = 2000
  }
  file {
    name = "file.conf"
  }
}

application.yml

server:
  port: 2004

spring:
  application:
    name: seata-account-service
  cloud:
    alibaba:
      seata:
        tx-service-group: fsp_tx_group
    nacos:
      discovery:
        server-addr: localhost:8848
  datasource:
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/seata_account
    username: root
    password: phoenix1991mh

logging:
  level:
    io:
      seata: info

mybatis:
  mapperLocations: classpath:mapper/*.xml