1、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。
2、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
3、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
4、 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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