背景

前段时间在看项目代码的时候，发现有些接口的流程比较长，在各个服务里面都有通过数据库事务保证数据的一致性，但是在上游的controller层并没有对一致性做保证。

网上查了下，还没找到基于Go开源的比较成熟的分布式事务框架。

于是，准备看看之前隔壁部门大佬写的tcc-transaction，这是一个基于tcc思想实现的分布式事务框架。

tcc分别代码Try，Confirm和Cancel。

Try: 尝试执行业务

完成所有业务检查（一致性）

预留必须业务资源（准隔离性）

Confirm: 确认执行业务

真正执行业务

不作任何业务检查

只使用Try阶段预留的业务资源

Confirm操作满足幂等性

Cancel: 取消执行业务

释放Try阶段预留的业务资源

Cancel操作满足幂等性

要了解其实现原理，第一步就是跑通项目自带的示例，即tcc-transaction-tutorial-sample部分的代码。

今天主要介绍在跑通tcc-transaction-tutorial-sample过程中遇到的各种坑。

依赖环境

Java
Maven
Git
MySQL
Redis
Zookeeper
Intellij IDEA

源码地址：https://github.com/changmingxie/tcc-transaction

我自己Fork了一份（配置改动已提交）：https://github.com/DMinerJackie/tcc-transaction

踩坑历程

踩坑准备

第一步：克隆代码

使用"git clone https://github.com/DMinerJackie/tcc-transaction"命令下载代码

第二步：导入代码并执行数据库脚本

代码导入Intellij IDEA。

执行tcc-transaction-http-sample/src/main/dbscripts 下的数据库脚本。

第三步：修改配置文件

主要修改的是数据库配置参数。拿tcc-transaction-dubbo-sample举例，需要修改的文件有

tcc-transaction/tcc-transaction-tutorial-sample/tcc-transaction-dubbo-sample/tcc-transaction-dubbo-capital/src/main/resources/tccjdbc.properties

tcc-transaction/tcc-transaction-tutorial-sample/tcc-transaction-dubbo-sample/tcc-transaction-dubbo-redpacket/src/main/resources/tccjdbc.properties

tcc-transaction/tcc-transaction-tutorial-sample/tcc-transaction-dubbo-sample/tcc-transaction-dubbo-order/src/main/resources/tccjdbc.properties

三个文件修改后对应配置如下

# 根据具体的MySQL版本使用驱动名称
jdbc.driverClassName=com.mysql.cj.jdbc.Driver
# 换成你连接数据库的地址
tcc.jdbc.url=jdbc:mysql://127.0.0.1:3306/TCC?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&useSSL=false
# 换成你需要配置数据库的用户名
jdbc.username=root
# 换成你需要配置数据库的密码
jdbc.password=rootroot

c3p0.initialPoolSize=10
c3p0.minPoolSize=10
c3p0.maxPoolSize=30
c3p0.acquireIncrement=3
c3p0.maxIdleTime=1800
c3p0.checkoutTimeout=30000

同时修改tcc-transaction-sample-capital、tcc-transaction-sample-redpacket和tcc-transaction-sample-order三个项目中jdbc.proerties文件的数据库连接，修改后配置如下

jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/TCC_CAP?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&useSSL=false
tcc.jdbc.url=jdbc:mysql://127.0.0.1:3306/TCC?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&useSSL=false
jdbc.username=root
jdbc.password=rootroot

c3p0.initialPoolSize=10
c3p0.minPoolSize=10
c3p0.maxPoolSize=30
c3p0.acquireIncrement=3
c3p0.maxIdleTime=1800
c3p0.checkoutTimeout=30000

第四步：启动项目

结合项目的README.md文件以及网上的文章了解到如果要跑通示例项目，需要分别启动三个项目。

tcc-transaction提供了两个版本：

基于dubbo通讯的示例版本
基于http通讯的示例版本

这两个版本对于的三个项目分别是

tcc-transaction-dubbo-capital（账户资产服务）、 tcc-transaction-dubbo-redpacket（红包服务）、 tcc-transaction-dubbo-order（交易订单服务）
tcc-transaction-http-capital（账户资产服务）、 tcc-transaction-http-redpacket（红包服务）、 tcc-transaction-http-order（交易订单服务）

其实这两个版本我都跑过，最终成功跑通的只有基于dubbo通讯的示例版本（http版本在最后confirm的时候最是失败，导致最终订单状态为unkown）。

以基于dubbo通讯的示例为例

tcc-transaction-dubbo-capital的启动配置如下

tcc-transaction-dubbo-redpacket的启动配置如下

tcc-transaction-dubbo-order的启动配置如下

坑1：连接不上zk

启动tcc-transaction-dubbo-capital项目，报错信息如下

[sample-dubbo-capital]2019-08-31 17:48:05,312 INFO  [org.apache.zookeeper.ZooKeeper] Initiating client connection, connectString=127.0.0.1:2181 sessionTimeout=30000 watcher=org.I0Itec.zkclient.ZkClient@32c7bb63
[sample-dubbo-capital]2019-08-31 17:48:05,334 INFO  [org.apache.zookeeper.ClientCnxn] Opening socket connection to server 127.0.0.1/127.0.0.1:2181. Will not attempt to authenticate using SASL (unknown error)
[sample-dubbo-capital]2019-08-31 17:48:05,344 WARN  [org.apache.zookeeper.ClientCnxn] Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect
java.net.ConnectException: Connection refused
	at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
	at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
	at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:361)
	at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1081)
[sample-dubbo-capital]2019-08-31 17:48:06,456 INFO  [org.apache.zookeeper.ClientCnxn] Opening socket connection to server 127.0.0.1/127.0.0.1:2181. Will not attempt to authenticate using SASL (unknown error)
[sample-dubbo-capital]2019-08-31 17:48:06,459 WARN  [org.apache.zookeeper.ClientCnxn] Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect
java.net.ConnectException: Connection refused
	at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
	at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
	at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:361)
	at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1081)
[sample-dubbo-capital]2019-08-31 17:48:07,566 INFO  [org.apache.zookeeper.ClientCnxn] Opening socket connection to server 127.0.0.1/127.0.0.1:2181. Will not attempt to authenticate using SASL (unknown error)
[sample-dubbo-capital]2019-08-31 17:48:07,567 WARN  [org.apache.zookeeper.ClientCnxn] Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect
java.net.ConnectException: Connection refused

从报错信息，一眼就看出是连不上zk即zookeeper。

这个很好理解，因为本地没有安装zk，于是安装并通过"./zkServer.sh start"启动zk

坑2：redis连不上

启动tcc-transaction-dubbo-order报错部分信息如下：

Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.mengyun.tcctransaction.sample.dubbo.order.service.PlaceOrderServiceImpl org.mengyun.tcctransaction.sample.dubbo.order.web.controller.OrderController.placeOrderService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'placeOrderServiceImpl': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.mengyun.tcctransaction.sample.dubbo.order.service.PaymentServiceImpl org.mengyun.tcctransaction.sample.dubbo.order.service.PlaceOrderServiceImpl.paymentService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'paymentServiceImpl': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.mengyun.tcctransaction.sample.dubbo.capital.api.CapitalTradeOrderService org.mengyun.tcctransaction.sample.dubbo.order.service.PaymentServiceImpl.capitalTradeOrderService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'captialTradeOrderService': Post-processing of FactoryBean's singleton object failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'compensableTransactionAspect' defined in class path resource [tcc-transaction.xml]: Cannot resolve reference to bean 'transactionConfigurator' while setting bean property 'transactionConfigurator'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'transactionConfigurator': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private org.mengyun.tcctransaction.TransactionRepository org.mengyun.tcctransaction.spring.support.SpringTransactionConfigurator.transactionRepository; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'transactionRepository' defined in file [/Users/jackie/workspace/tcc-transaction/tcc-transaction-tutorial-sample/tcc-transaction-dubbo-sample/tcc-transaction-dubbo-order/target/tcc-transaction-dubbo-order-1.2.6/WEB-INF/classes/config/spring/local/appcontext-service-tcc.xml]: Error setting property values; nested exception is org.springframework.beans.PropertyBatchUpdateException; nested PropertyAccessExceptions (1) are:
PropertyAccessException 1: org.springframework.beans.MethodInvocationException: Property 'jedisPool' threw exception; nested exception is redis.clients.jedis.exceptions.JedisConnectionException: Could not get a resource from the pool
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:526)
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:295)
	... 60 more

这个和上面的原因类似，本地没有安装redis，导致无法拿到redis连接。

于是安装redis，并使用"redis-server"启动redis。

坑3：Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection

三个项目都启动后，可以看到一个商品链接列表页，但是在点击链接后无法跳转，并且报错如下

Type Exception Report
Message Request processing failed; nested exception is org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.PersistenceException:
Description The server encountered an unexpected condition that prevented it from fulfilling the request.
Exception
org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
### The error may exist in URL [jar:file:/Users/jackie/workspace/tcc-transaction/tcc-transaction-tutorial-sample/tcc-transaction-http-sample/tcc-transaction-http-order/target/tcc-transaction-http-order-1.2.6/WEB-INF/lib/tcc-transaction-sample-order-1.2.6.jar!/config/sqlmap/main/sample-product.xml]
### The error may involve org.mengyun.tcctransaction.sample.order.infrastructure.dao.ProductDao.findByShopId
### The error occurred while executing a query
### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:965)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:844)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:829)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:106)

Root Cause
org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
### The error may exist in URL [jar:file:/Users/jackie/workspace/tcc-transaction/tcc-transaction-tutorial-sample/tcc-transaction-http-sample/tcc-transaction-http-order/target/tcc-transaction-http-order-1.2.6/WEB-INF/lib/tcc-transaction-sample-order-1.2.6.jar!/config/sqlmap/main/sample-product.xml]

根据错误信息，排查是MySQL版本和数据库驱动版本不匹配。

本地的MySQL版本是"8.0.11 MySQL Community Server - GPL"，但是tcc-transaction中对应的驱动版本是

<dependency>
		<groupId>mysql</groupId>
		<artifactId>mysql-connector-java</artifactId>
		<version>5.1.33</version>
</dependency>

改为

<dependency>
		<groupId>mysql</groupId>
		<artifactId>mysql-connector-java</artifactId>
		<version>8.0.11</version>
</dependency>

同时针对高版本，需要在连接的jdbc-url后面加上useSSL=false

坑4：Loading class `com.mysql.jdbc.Driver'. This is deprecated

启动tcc-transaction-dubbo-redpacket时，在日志中看到一个警告"Loading class `com.mysql.jdbc.Driver'. This is deprecated"。

通过搜索，发现是因为数据库驱动com.mysql.jdbc.Driver'已经被弃用了，需要使用com.mysql.cj.jdbc.Driver，于是修改jdbc.proerties的配置（具体配置见上面），启动正常。

踩完上面的坑后，启动三个项目，完整走完流程，实现了一个基于分布式事务的商品购买行为，具体过程如下图所示

总结

运行示例项目的过程不算太顺利，主要有一下几个原因吧

本地环境配置和项目提供的不一致，导致走了很多弯路，比如MySQL的版本。
缺少详细的跑示例项目的文档说明。
网上提供的资料比较粗略，也比较陈旧，文中能跑起来的步骤说明已经不适用现在的代码了。

所以，在踩完这么多坑总结下，避免后面的人走同样的弯路。

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