RedisTemplate使用事务处理

首先从使用springboot+redis碰到的一个问题说起。在前几篇文章中介绍了用SpringBoot+redis构建了一个个人博客。在刚开始远行的时候发现发了几个请求操作了几次redis之后，后面的就被阻塞了，请求一直在等待返回，我们重现一下问题。
[注意] 该问题只会出现在springboot 2.0之前的版本;2.0之后springboot连接Redis改成了lettuce，并重新实现，问题已经不存在

打开Template的事务支持

POM 配置：

<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.github.springboot</groupId> <artifactId>redis-tx-demo</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>SpringBoot redis TX demo</name> <description>Demo project for Spring Boot with Redis transaction</description> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.5.2.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-rest</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project> 

Redis configuration (EnbaleTransactionSupport设为true):

@Configuration public class RedisConfiguration { @Bean public StringRedisTemplate redisTemplate(RedisConnectionFactory redisConnectionFactory) { StringRedisTemplate template = new StringRedisTemplate(); template.setConnectionFactory(redisConnectionFactory); template.setEnableTransactionSupport(true); //打开事务支持 return template; } } 

Controller就是简单的set一个key到redis:

@RestController public class DemoController { private StringRedisTemplate template; public DemoController(StringRedisTemplate template) { this.template = template; } @GetMapping("/put") public String redisSet() { int i = (int)(Math.random() * 100); template.opsForValue().set("key"+i, "value"+i, 300, TimeUnit.SECONDS); return "success "+"key"+i; } } 

启动后，我们使用RestClient发送请求http://localhost:8080/put，发送8次之后就会发现没有返回了。这个时候我们查看redis的链接数，发现已经超过8个，springboot对于jedis连接池默认的最大活跃连接数是8，所以看出来是连接池被耗光了。

127.0.0.1:6379> info clients # Clients connected_clients:9 client_longest_output_list:0 client_biggest_input_buf:0 blocked_clients:0 127.0.0.1:6379> 

还有查看程序的日志可以发现，RedisConnectionUtils只有Opening RedisConnection而没有close。

2018-08-11 11:00:48.889 [DEBUG][http-nio-8080-exec-8]:o.s.data.redis.core.RedisConnectionUtils [doGetConnection:126] Opening RedisConnection 2018-08-11 11:00:50.169 [DEBUG][http-nio-8080-exec-8]:o.s.w.s.m.m.a.RequestResponseBodyMethodProcessor [writeWithMessageConverters:249] Written [success key39] as "text/plain" using [org.springframework.http.converter.StringHttpMessageConverter@766a49c7] 2018-08-11 11:00:50.170 [DEBUG][http-nio-8080-exec-8]:org.springframework.web.servlet.DispatcherServlet [processDispatchResult:1044] Null ModelAndView returned to DispatcherServlet with name 'dispatcherServlet': assuming HandlerAdapter completed request handling 2018-08-11 11:00:50.170 [DEBUG][http-nio-8080-exec-8]:org.springframework.web.servlet.DispatcherServlet [processRequest:1000] Successfully completed request 2018-08-11 11:00:50.170 [DEBUG][http-nio-8080-exec-8]:o.s.boot.web.filter.OrderedRequestContextFilter [doFilterInternal:104] Cleared thread-bound request context: org.apache.catalina.connector.RequestFacade@c03b2d8 2018-08-11 11:00:53.854 [DEBUG][http-nio-8080-exec-9]:o.s.boot.web.filter.OrderedRequestContextFilter [initContextHolders:114] Bound request context to thread: org.apache.catalina.connector.RequestFacade@c03b2d8 2018-08-11 11:00:53.856 [DEBUG][http-nio-8080-exec-9]:org.springframework.web.servlet.DispatcherServlet [doService:865] DispatcherServlet with name 'dispatcherServlet' processing GET request for [/put] 2018-08-11 11:00:53.857 [DEBUG][http-nio-8080-exec-9]:o.s.w.s.m.m.a.RequestMappingHandlerMapping [getHandlerInternal:310] Looking up handler method for path /put 2018-08-11 11:00:53.857 [DEBUG][http-nio-8080-exec-9]:o.s.w.s.m.m.a.RequestMappingHandlerMapping [getHandlerInternal:317] Returning handler method [public java.lang.String com.github.springboot.demo.DemoController.redisSet()] 2018-08-11 11:00:53.858 [DEBUG][http-nio-8080-exec-9]:o.s.b.factory.support.DefaultListableBeanFactory [doGetBean:251] Returning cached instance of singleton bean 'demoController' 2018-08-11 11:00:53.858 [DEBUG][http-nio-8080-exec-9]:org.springframework.web.servlet.DispatcherServlet [doDispatch:951] Last-Modified value for [/put] is: -1 2018-08-11 11:00:53.861 [DEBUG][http-nio-8080-exec-9]:o.s.data.redis.core.RedisConnectionUtils [doGetConnection:126] Opening RedisConnection 

关闭template的事务支持

接下来我们修改一下RedisConfiguration的配置，不启用事务管理，

@Bean public StringRedisTemplate redisTemplate(RedisConnectionFactory redisConnectionFactory) { StringRedisTemplate template = new StringRedisTemplate(); template.setConnectionFactory(redisConnectionFactory); // template.setEnableTransactionSupport(true); //禁用事务支持 return template; } 

重新测试一下，发现是正常的，redis的client链接数一直保持在2。程序日志里的也可以看到Redis Connection关闭的日志。

2018-08-11 15:55:19.975 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [doGetConnection:126] Opening RedisConnection 2018-08-11 15:55:20.029 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [releaseConnection:210] Closing Redis Connection 2018-08-11 15:55:20.056 [DEBUG][http-nio-8080-exec-1]:o.s.w.s.m.m.a.RequestResponseBodyMethodProcessor [writeWithMessageConverters:249] Written [success key72] as "text/plain" using [org.springframework.http.converter.StringHttpMessageConverter@51ab1ee3] 

也就是说，如果我们把事务的支持打开，spring在每次操作之后是不会主动关闭连接的。我们去RedisTemplate的源码中找下原因。

public ValueOperations<K, V> opsForValue() { if (valueOps == null) { valueOps = new DefaultValueOperations<K, V>(this); } return valueOps; } 

可以发现template.opsForValue().set()操作最终是调用的DefaultValueOperations中的set()方法，继续跟进去最终调用的RedisTemplate中的execute(RedisCallback<T> action, boolean exposeConnection, boolean pipeline)方法。

public <T> T execute(RedisCallback<T> action, boolean exposeConnection, boolean pipeline) { Assert.isTrue(initialized, "template not initialized; call afterPropertiesSet() before using it"); Assert.notNull(action, "Callback object must not be null"); RedisConnectionFactory factory = getConnectionFactory(); RedisConnection conn = null; try { if (enableTransactionSupport) { // only bind resources in case of potential transaction synchronization conn = RedisConnectionUtils.bindConnection(factory, enableTransactionSupport); } else { conn = RedisConnectionUtils.getConnection(factory); } boolean existingConnection = TransactionSynchronizationManager.hasResource(factory); RedisConnection connToUse = preProcessConnection(conn, existingConnection); boolean pipelineStatus = connToUse.isPipelined(); if (pipeline && !pipelineStatus) { connToUse.openPipeline(); } RedisConnection connToExpose = (exposeConnection ? connToUse : createRedisConnectionProxy(connToUse)); T result = action.doInRedis(connToExpose); // close pipeline if (pipeline && !pipelineStatus) { connToUse.closePipeline(); } // TODO: any other connection processing? return postProcessResult(result, connToUse, existingConnection); } finally { RedisConnectionUtils.releaseConnection(conn, factory); } } 

可以看到获取连接的操作也针对打开事务支持的template有特殊的处理逻辑。这里我们先跳过，先看看最终肯定会走到的RedisConnectionUtils.releaseConnection(conn, factory)这一步。

/** * Closes the given connection, created via the given factory if not managed externally (i.e. not bound to the * thread). * * @param conn the Redis connection to close * @param factory the Redis factory that the connection was created with */ public static void releaseConnection(RedisConnection conn, RedisConnectionFactory factory) { if (conn == null) { return; } RedisConnectionHolder connHolder = (RedisConnectionHolder) TransactionSynchronizationManager.getResource(factory); if (connHolder != null && connHolder.isTransactionSyncronisationActive()) { if (log.isDebugEnabled()) { log.debug("Redis Connection will be closed when transaction finished."); } return; } // release transactional/read-only and non-transactional/non-bound connections. // transactional connections for read-only transactions get no synchronizer registered if (isConnectionTransactional(conn, factory) && TransactionSynchronizationManager.isCurrentTransactionReadOnly()) { unbindConnection(factory); } else if (!isConnectionTransactional(conn, factory)) { if (log.isDebugEnabled()) { log.debug("Closing Redis Connection"); } conn.close(); } } 

可以看到针对打开事务支持的template,只是解绑了连接，根本没有做close的操作。关于什么是解绑，其实这个方法的注释中已经说的比较清楚了，对于开启了事务的Template，由于已经绑定了线程中连接，所以这里是不会关闭的，只是做了解绑的操作。
到这里原因就很清楚了，就是只要template开启了事务支持，spring就认为只要使用这个template就会包含在事务当中，因为一个事务中的操作必须在同一个连接中完成，所以在每次get/set之后，template是不会关闭链接的，因为它不知道事务有没有结束。

使用@Transanctional注解支持Redis事务

既然RedisTemlate在setEnableTransactionSupport会造成连接不关闭，那怎么样才能正常关闭呢？我们将事务支持开关和@Transanctional结合起来用看看会怎么样。
spring中要使用@Transanctional首先要配transactionManager，但是spring没有专门针对Redis的事务管理器实现，而是所有调用RedisTemplate的方法最终都会调用到RedisConnctionUtils这个类的方法上面，在这个类里面会判断是不是进入到事务里面，也就是说Redis的事务管理的功能是由RedisConnctionUtils内部实现的。
根据官方文档，我只想用Redis事务，也必须把JDBC捎上。当然反过来讲，不依赖数据的项目确实不多，貌似这么实现影响也不大。下面我们先根据官方文档配置一下看看效果。
首先修改POM配置，添加两个依赖。如果项目里本来已经使用了数据库，那这一步就不需要了。

<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-jdbc</artifactId> </dependency> <dependency> <groupId>com.h2database</groupId> <artifactId>h2</artifactId> <scope>runtime</scope> </dependency> 

然后修改RedisConfiguration

@Bean public StringRedisTemplate redisTemplate(RedisConnectionFactory redisConnectionFactory) { StringRedisTemplate template = new StringRedisTemplate(); template.setConnectionFactory(redisConnectionFactory); template.setEnableTransactionSupport(true);//打开事务支持 return template; } //配置事务管理器 @Bean public PlatformTransactionManager transactionManager(DataSource dataSource) throws SQLException { return new DataSourceTransactionManager(dataSource); } 

我们新建一个RedisService，将原来的数据操作移到service里面。同时将Service方法加上@Transactional注解。

@Service public class RedisService { private StringRedisTemplate template; public RedisService(StringRedisTemplate template) { this.template = template; } @Transactional public String put() { int i = (int)(Math.random() * 100); template.opsForValue().set("key"+i, "value"+i, 300, TimeUnit.SECONDS); return "success "+"key"+i; } } //----------------------------------------------------------- //controller里面加一个新的方法，调用Service @GetMapping("/puttx") public String redisTxSet() { return redisService.put(); } 

完成这些工作之后，再往http://localhost:8080/puttx发送请求，无论点多少次，Redis的连接数始终维持在1个不变。在看程序的输出日志里面我们也发现了，事务结束后连接被正常释放。因为使用了JDBC的事务管理器，所以还顺便做了一次数据库事务的开启和提交。还有一点值得注意的是，跟数据库一样，使用注解来做事务管理，spring也会主动管理redis事务的提交和回滚，也就是在之前发送一条MULTI命令，成功后发送EXEC，失败后发送DISCARD。

2018-08-11 20:57:04.990 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [doGetConnection:126] Opening RedisConnection 2018-08-11 20:57:04.990 [DEBUG][http-nio-8080-exec-1]:o.springframework.aop.framework.JdkDynamicAopProxy [getProxy:118] Creating JDK dynamic proxy: target source is SingletonTargetSource for target object [org.springframework.data.redis.connection.jedis.JedisConnection@20f2be3c] 2018-08-11 20:57:04.990 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'multi' on bound conneciton 2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'isPipelined' on bound conneciton 2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'setEx' on bound conneciton 2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [releaseConnection:198] Redis Connection will be closed when transaction finished. 2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.jdbc.datasource.DataSourceTransactionManager [processCommit:759] Initiating transaction commit 2018-08-11 20:57:04.991 [DEBUG][http-nio-8080-exec-1]:o.s.jdbc.datasource.DataSourceTransactionManager [doCommit:310] Committing JDBC transaction on Connection [ProxyConnection[PooledConnection[conn9: url=jdbc:h2:mem:testdb user=SA]]] 2018-08-11 20:57:04.992 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'exec' on bound conneciton 2018-08-11 20:57:04.992 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [afterCompletion:306] Closing bound connection after transaction completed with 0 2018-08-11 20:57:04.992 [DEBUG][http-nio-8080-exec-1]:o.s.data.redis.core.RedisConnectionUtils [intercept:337] Invoke 'close' on bound conneciton 2018-08-11 20:57:04.993 [DEBUG][http-nio-8080-exec-1]:o.s.jdbc.datasource.DataSourceTransactionManager [doCleanupAfterCompletion:368] Releasing JDBC Connection [ProxyConnection[PooledConnection[conn9: url=jdbc:h2:mem:testdb user=SA]]] after transaction 2018-08-11 20:57:04.993 [DEBUG][http-nio-8080-exec-1]:o.springframework.jdbc.datasource.DataSourceUtils [doReleaseConnection:327] Returning JDBC Connection to DataSource 

总结

在spring中要使用Redis注解式事务，首先要设置RedisTemplate的enableTransactionSupport属性为true，然后配置一个jdbc的事务管理器。
这里有一点非常重要，一旦这样配置，所有使用这个template的redis操作都必须走注解式事务，要不然会导致连接一直占用，不关闭。

建议

• 升级到springboot 2.0以上版本，如果因为项目原因无法升级看下面的建议
• 如果使用Redis事务的场景不多，完全可以自己管理，不需要使用spring的注解式事务。如下面这样使用：

List<Object> txResults = redisTemplate.execute(new SessionCallback<List<Object>>() { public List<Object> execute(RedisOperations operations) throws DataAccessException { operations.multi(); operations.opsForSet().add("key", "value1"); // This will contain the results of all ops in the transaction return operations.exec(); } }); 

• 如果一定要使用spring提供的注解式事务，建议初始化两个RedisTemplate Bean，分别设置enableTransactionSupport属性为true和false。针对需要事务和不需要事务的操作使用不同的template。
• 从个人角度，我不建议使用redis事务，因为redis对于事务的支持并不是关系型数据库那样满足ACID。Redis事务只能保证ACID中的隔离性和一致性，无法保证原子性和持久性。而我们使用事务最重要的一个理由就是原子性，这一点无法保证，事务的意义就去掉一大半了。所以事务的场景可以尝试通过业务代码来实现。

本篇博客使用的代码：https://github.com/chilexun/springboot-demo.git