16.Spring Cloud Alibaba学习笔记--Seata案例--原理
TC/TM/RM三个组件的近似理解
- TC（Transaction Coordinator） —— Seata 服务器
- TM（Transaction Manager）—— 带有
@GlobalTransactional的方法，事务的发起方 - RM（Resource Manager）—— 订单 / 库存 / 账户这三个数据库，事务的参与方
分布式事务的执行流程
- TM 开启分布式事务（TM 向 TC 注册全局事务记录）；
- 按业务场景，编排数据库、服务等事务内资源（RM 向 TC 汇报资源准备状态）；
- TM 结束分布式事务，事务一阶段结束（TM 通知 TC 提交 / 回滚分布式事务）；
- TC 汇报事务信息，决定分布式事务是提交还是回滚；
- TC 通知所有 RM 提交 / 回滚资源，事务二阶段结束。
AT模式如何做到对业务的无侵入
AT模式简介
前提
- 基于支持本地 ACID 事务的关系型数据库。
- Java 应用，通过 JDBC 访问数据库。
整体机制
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。
参考：
http://seata.io/zh-cn/docs/overview/what-is-seata.html
AT 模式对应于阿里云的全局事务服务（Global Transaction Service，简称 GTS）。
一阶段加载
在一阶段，Seata 拦截“业务 SQL”：
- 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”（前置镜像）；
- 执行“业务 SQL”更新业务数据；
- 在业务数据更新之后，其保存成"after image” （后置镜像），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。
官方的过程可参考：
http://seata.io/zh-cn/docs/dev/mode/at-mode.html
二阶段提交
二阶段如果顺利提交的话，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。回滚方式便是用“before image”还原业务数据；但在还原前要首先要校验脏写 ，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 。
通过 DEBUG 了解 Seata 原理
打断点
1、以 DEBUG 模式启动
seata-order-service2001，seata-storage-service2002，seata-account-service2003
2、打断点
在 seata-account-service2003 的 AccountServiceImpl 中打断点
3、刷新网址
http://localhost:2001/order/create?userId=1&productId=1&count=10&money=100
4、查看数据库
seata -> branch_table
| branch_id | xid | transaction_id | resource_group_id | resource_id | lock_key | branch_type | status | client_id | application_data | gmt_create | gmt_modified |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2051276927 | 192.168.25.141:8091:2051276925 | 2051276925 | jdbc:mysql://192.168.25.158:3306/seata_order | t_order:17 | AT | 2 | seata-order-service:192.168.25.141:61317 | 2020-8-16 12:14:23 | 2020-8-16 12:14:23 | ||
| 2051276931 | 192.168.25.141:8091:2051276925 | 2051276925 | jdbc:mysql://192.168.25.158:3306/seata_storage | t_storage:1 | AT | 2 | seata-storage-service:192.168.25.141:61184 | 2020-8-16 12:14:23 | 2020-8-16 12:14:23 | ||
| 2051276934 | 192.168.25.141:8091:2051276925 | 2051276925 | jdbc:mysql://192.168.25.158:3306/seata_account | t_account:1 | AT | 2 | seata-account-service:192.168.25.141:61232 | 2020-8-16 12:14:23 | 2020-8-16 12:14:23 |
seata -> global_table
| xid | transaction_id | status | application_id | transaction_service_group | transaction_name | timeout | begin_time | application_data | gmt_create | gmt_modified |
|---|---|---|---|---|---|---|---|---|---|---|
| 192.168.25.141:8091:2051276925 | 2051276925 | 5 | seata-order-service | fsp_tx_group | fsp-create-order | 60000 | 1597551263304 | 2020-8-16 12:14:23 | 2020-8-16 12:14:54 |
seata -> lock_table
| row_key | xid | transaction_id | branch_id | resource_id | table_name | pk | gmt_create | gmt_modified |
|---|---|---|---|---|---|---|---|---|
| jdbc:mysql://192.168.25.158:3306/seata_account^^t_account^^1 | 192.168.25.141:8091:2051276925 | 2051276925 | 2051276934 | jdbc:mysql://192.168.25.158:3306/seata_account | t_account | 1 | 2020-8-16 12:14:23 | 2020-8-16 12:14:23 |
| jdbc:mysql://192.168.25.158:3306/seata_order^^t_order^^17 | 192.168.25.141:8091:2051276925 | 2051276925 | 2051276927 | jdbc:mysql://192.168.25.158:3306/seata_order | t_order | 17 | 2020-8-16 12:14:23 | 2020-8-16 12:14:23 |
| jdbc:mysql://192.168.25.158:3306/seata_storage^^t_storage^^1 | 192.168.25.141:8091:2051276925 | 2051276925 | 2051276931 | jdbc:mysql://192.168.25.158:3306/seata_storage | t_storage | 1 | 2020-8-16 12:14:23 | 2020-8-16 12:14:23 |
seata_order -> undo_log
| id | branch_id | xid | context | rollback_info | log_status | log_created | log_modified | ext |
|---|---|---|---|---|---|---|---|---|
| 11 | 2051276927 | 192.168.25.141:8091:2051276925 | serializer=jackson | 见下方 | 0 | 2020-8-16 12:14:23 | 2020-8-16 12:14:23 |
seata_order -> undo_log -> rollback_info
{
"@class": "io.seata.rm.datasource.undo.BranchUndoLog",
"xid": "192.168.25.141:8091:2051276925",
"branchId": 2051276927,
"sqlUndoLogs": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.undo.SQLUndoLog",
"sqlType": "INSERT",
"tableName": "t_order",
"beforeImage": {
"@class": "io.seata.rm.datasource.sql.struct.TableRecords$EmptyTableRecords",
"tableName": "t_order",
"rows": [
"java.util.ArrayList",
[]
]
},
"afterImage": {
"@class": "io.seata.rm.datasource.sql.struct.TableRecords",
"tableName": "t_order",
"rows": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Row",
"fields": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "id",
"keyType": "PrimaryKey",
"type": -5,
"value": [
"java.lang.Long",
17
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "user_id",
"keyType": "NULL",
"type": -5,
"value": [
"java.lang.Long",
1
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "product_id",
"keyType": "NULL",
"type": -5,
"value": [
"java.lang.Long",
1
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "count",
"keyType": "NULL",
"type": 4,
"value": 10
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "money",
"keyType": "NULL",
"type": 3,
"value": [
"java.math.BigDecimal",
100
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "status",
"keyType": "NULL",
"type": 4,
"value": 0
}
]
]
}
]
]
}
}
]
]
}
seata_storage -> undo_log
| id | branch_id | xid | context | rollback_info | log_status | log_created | log_modified | ext |
|---|---|---|---|---|---|---|---|---|
| 11 | 2051276931 | 192.168.25.141:8091:2051276925 | serializer=jackson | 见下方 | 0 | 2020-8-16 12:14:23 | 2020-8-16 12:14:23 |
seata_storage -> undo_log -> rollback_info
{
"@class": "io.seata.rm.datasource.undo.BranchUndoLog",
"xid": "192.168.25.141:8091:2051276925",
"branchId": 2051276931,
"sqlUndoLogs": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.undo.SQLUndoLog",
"sqlType": "UPDATE",
"tableName": "t_storage",
"beforeImage": {
"@class": "io.seata.rm.datasource.sql.struct.TableRecords",
"tableName": "t_storage",
"rows": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Row",
"fields": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "id",
"keyType": "PrimaryKey",
"type": -5,
"value": [
"java.lang.Long",
1
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "used",
"keyType": "NULL",
"type": 4,
"value": 20
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "residue",
"keyType": "NULL",
"type": 4,
"value": 80
}
]
]
}
]
]
},
"afterImage": {
"@class": "io.seata.rm.datasource.sql.struct.TableRecords",
"tableName": "t_storage",
"rows": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Row",
"fields": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "id",
"keyType": "PrimaryKey",
"type": -5,
"value": [
"java.lang.Long",
1
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "used",
"keyType": "NULL",
"type": 4,
"value": 30
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "residue",
"keyType": "NULL",
"type": 4,
"value": 70
}
]
]
}
]
]
}
}
]
]
}
seata_account -> undo_log
| id | branch_id | xid | context | rollback_info | log_status | log_created | log_modified | ext |
|---|---|---|---|---|---|---|---|---|
| 2 | 2051276842 | 192.168.25.141:8091:2051276834 | serializer=jackson | {} | 1 | 2020-8-16 12:06:26 | 2020-8-16 12:06:26 | |
| 7 | 2051276934 | 192.168.25.141:8091:2051276925 | serializer=jackson | 见下方 | 0 | 2020-8-16 12:14:23 | 2020-8-16 12:14:23 |
seata_account -> undo_log -> rollback_info
{
"@class": "io.seata.rm.datasource.undo.BranchUndoLog",
"xid": "192.168.25.141:8091:2051276925",
"branchId": 2051276934,
"sqlUndoLogs": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.undo.SQLUndoLog",
"sqlType": "UPDATE",
"tableName": "t_account",
"beforeImage": {
"@class": "io.seata.rm.datasource.sql.struct.TableRecords",
"tableName": "t_account",
"rows": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Row",
"fields": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "id",
"keyType": "PrimaryKey",
"type": -5,
"value": [
"java.lang.Long",
1
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "residue",
"keyType": "NULL",
"type": 3,
"value": [
"java.math.BigDecimal",
800
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "used",
"keyType": "NULL",
"type": 3,
"value": [
"java.math.BigDecimal",
200
]
}
]
]
}
]
]
},
"afterImage": {
"@class": "io.seata.rm.datasource.sql.struct.TableRecords",
"tableName": "t_account",
"rows": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Row",
"fields": [
"java.util.ArrayList",
[
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "id",
"keyType": "PrimaryKey",
"type": -5,
"value": [
"java.lang.Long",
1
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "residue",
"keyType": "NULL",
"type": 3,
"value": [
"java.math.BigDecimal",
700
]
},
{
"@class": "io.seata.rm.datasource.sql.struct.Field",
"name": "used",
"keyType": "NULL",
"type": 3,
"value": [
"java.math.BigDecimal",
300
]
}
]
]
}
]
]
}
}
]
]
}
放行后继续执行
异步任务阶段的分支提交请求将异步和批量地删除相应 UNDO LOG 记录。
- seata -> branch_table
- seata -> global_table
- seata -> lock_table
- seata_order -> undo_log
- seata_storage -> undo_log
- seata_account -> undo_log
内容被全部删除。
总体执行流程
