SpringCloudAlibaba-分布式事务-Seata

一、概述

Seata(Simple Extensible Autonomous Transaction Architecture 简单的可扩展自治事务架构) 是阿里巴巴开源的分布式事务中间件，致力于提供高性能，零入侵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，为用户打造一站式的分布式解决方案。

Seata 的设计思路是将一个分布式事务可以理解成一个全局事务，下面挂了若干个分支事务，而一个分支事务是一个满足 ACID 的本地事务，因此我们可以操作分布式事务像操作本地事务一样。

二、Seata相关术语一.TC (Transaction Coordinator) - 事务协调者

维护全局和分支事务的状态，驱动全局事务提交或回滚。

二.TM (Transaction Manager) - 事务管理器

定义全局事务的范围：开始全局事务、提交或回滚全局事务。

三.RM (Resource Manager) - 资源管理器

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。

四.Transcation ID（XID）

由事务协调者创建的全局唯一的事务ID

三、Seata 工作流程一.AT 模式工作机制(默认模式，二阶段提交,DB中实现)

两阶段提交协议的演变：

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。

1、一阶段（拦截SQL，解析数据，保存原数据快照与更新后快照）

拦截业务SQL，根据业务SQL解析出需要修改或者提交的表的原数据，统一放入before image的快照当中。然后更新业务数据，将更新后的数据放入after image当中。此事会进行行锁，避免其他数据进行脏读。

2、二阶段 1.事务成功

因为业务SQL已经更新过了，只需要将第一阶段保存的快照数据删掉，解锁行锁即可。

2.事务回滚

事务回滚操作就比较复杂了，分为三步。

(1).校验脏读

比较after image中的数据和数据库数据，如果两份数据完全一致，则说明没有进行脏写。

(2).还原数据

将before image 中的数据你想SQL进行数据还原

(3).删除中间数据

删除before image和after image中的数据，并且解锁。

二.TCC 模式（二阶段提交，需要用户自己去实现）

TCC模式需要用户根据自己的业务实现Try，/confirm/i，Cancel三个操作。TCC模式侵入式比较强，AT模式无侵入，但是AT模式会有行锁，效率较差。
TCC 模型的隔离性思想就是通过业务的改造，在第一阶段结束之后，从底层数据库资源层面的加锁过渡为上层业务层面的加锁，从而释放底层数据库锁资源，放宽分布式事务锁协议，将锁的粒度降到最低，以最大限度提高业务并发性能。

1、try

预留资源

2、confirm

完成业务

3、concel

发生回滚，释放Try阶段预留的资源

三.Saga 模式

之后再补充

四、Seata配置文件一.file.conf（持久化配置文件）

## transaction log store, only used in seata-server 事务日志存储，仅用于 seata-server
store {
  ## store mode: file、db、redis
  mode = "db" #事务日志存储模式文件、数据库、redis
  ## rsa decryption public key
  publicKey = ""
  ## 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)/HikariDataSource(hikari) etc.
    datasource = "druid" #数据库连接池选择
    ## mysql/oracle/postgresql/h2/oceanbase etc.
    dbType = "mysql" #数据库选择
    ##driverClassName = "com.mysql.jdbc.Driver" #5.0版本SQL驱动
	driverClassName = "com.mysql.cj.jdbc.Driver" ##8.0版本SQL驱动
    ## if using mysql to store the data, recommend add rewriteBatchedStatements=true in jdbc connection param
    ## url = "jdbc:mysql://139.155.49.250:3306/seata?rewriteBatchedStatements=true" ##5.0版本url
	url = "jdbc:mysql://127.0.0.1:3306/seata?useSSL=false&&serverTimezone=GMT%2B8&useInformationSchema=true" ##5.0版本url
    user = "root"
    password = "xxxxxxx"
    minConn = 5
    maxConn = 100
    globalTable = "global_table" ##三张表名
    branchTable = "branch_table"
    lockTable = "lock_table"
    queryLimit = 100
    maxWait = 5000
  }

  ## redis store property
  redis {
    ## redis mode: single、sentinel
    mode = "single"
    ## single mode property
    single {
      host = "127.0.0.1"
      port = "6379"
    }
    ## sentinel mode property
    sentinel {
      masterName = ""
      ## such as "10.28.235.65:26379,10.28.235.65:26380,10.28.235.65:26381"
      sentinelHosts = ""
    }
    password = ""
    database = "0"
    minConn = 1
    maxConn = 10
    maxTotal = 100
    queryLimit = 100
  }
}

二.registry.conf（注册中心配置文件）

registry {
  # file 、nacos 、eureka、redis、zk、consul、etcd3、sofa
  type = "nacos" ##注册中心支持的模式

  nacos {
    application = "seata-server" ##服务名称
    serverAddr = "119.91.99.85:8849"  ##注册中心IP
    group = "SEATA_GROUP" ##分组
    namespace = "public" ## 命名空间
    cluster = "default" ##是否集群
    username = "nacos" ##nacos账务密码
    password = "nacos"
  }
  eureka {
    serviceUrl = "http://localhost:8761/eureka"
    application = "default"
    weight = "1"
  }
  redis {
    serverAddr = "localhost:6379"
    db = 0
    password = ""
    cluster = "default"
    timeout = 0
  }
  zk {
    cluster = "default"
    serverAddr = "127.0.0.1:2181"
    sessionTimeout = 6000
    connectTimeout = 2000
    username = ""
    password = ""
  }
  consul {
    cluster = "default"
    serverAddr = "127.0.0.1:8500"
    aclToken = ""
  }
  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"
  }
}
## 配置中心
config {
  # file、nacos 、apollo、zk、consul、etcd3
  type = "nacos"

  nacos {
    serverAddr = "119.91.99.85:8849"
    namespace = "public"
    group = "SEATA_GROUP"
    username = "nacos"
    password = "nacos"
    dataId = "seataServer.properties"
  }
  consul {
    serverAddr = "127.0.0.1:8500"
    aclToken = ""
  }
  apollo {
    appId = "seata-server"
    ## apolloConfigService will cover apollometa
    apollometa = "http://192.168.1.204:8801"
    apolloConfigService = "http://192.168.1.204:8080"
    namespace = "application"
    apolloAccesskeySecret = ""
    cluster = "seata"
  }
  zk {
    serverAddr = "127.0.0.1:2181"
    sessionTimeout = 6000
    connectTimeout = 2000
    username = ""
    password = ""
    nodePath = "/seata/seata.properties"
  }
  etcd3 {
    serverAddr = "http://localhost:2379"
  }
  file {
    name = "file.conf"
  }
}

三.服务端SQL脚本（1.4.2版本）

源链接

https://github.com/seata/seata/tree/develop/script/server

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(128),
    `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;

CREATE TABLE IF NOT EXISTS `distributed_lock`
(
    `lock_key`       CHAR(20) NOT NULL,
    `lock_value`     VARCHAR(20) NOT NULL,
    `expire`         BIGINT,
    primary key (`lock_key`)
) ENGINE = InnoDB
  DEFAULT CHARSET = utf8mb4;

INSERT INTO `distributed_lock` (lock_key, lock_value, expire) VALUES ('AsyncCommitting', ' ', 0);
INSERT INTO `distributed_lock` (lock_key, lock_value, expire) VALUES ('RetryCommitting', ' ', 0);
INSERT INTO `distributed_lock` (lock_key, lock_value, expire) VALUES ('RetryRollbacking', ' ', 0);
INSERT INTO `distributed_lock` (lock_key, lock_value, expire) VALUES ('TxTimeoutCheck', ' ', 0);

四.客户端SQL脚本（1.4.2版本）

客户端SQL脚本根据不同的模式有不同的SQL脚本，这里的是AT模式的

https://github.com/seata/seata/tree/develop/script/client

-- for AT mode you must to init this sql for you business database. the seata server not need it.
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 = utf8 COMMENT ='AT transaction mode undo table';

五、案例（配置中心Nacos，注册中心Nacos）

SpringCloudAlibaba-分布式事务-Seata

Java相关栏目本月热门文章