你知道 Redis 可以实现延迟队列吗？

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"最近，又重新学习了下Redis，深深被Redis的魅力所折服，Redis不仅能快还能慢（我想也这么优秀o(╥﹏╥)o），简直利器呀","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"咳咳咳，大家不要误会，本文很正经的啦！伙伴们跟我一起冲呀，我们一起去爬爬这座延时队列的山峰，探一探它究竟到底有高。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5c/5c882a393a530f984df1215ad1709de9.png","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果觉得本文有收获的话，二哈恳求各位伙伴们点个小心心，♥(ˆ◡ˆԅ)（（づ￣3￣）づ╭❤～哟）。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那接下来开始我们的旅行啦~，我们都知道Redis是一种基于内存的单进程单线程数据库（Redis6.0开始之后支持多线程啦！），处理速度都非常快。那么为何Redis又能慢呢？原来，这里说的慢是指Redis可以设置一些参数达到慢处理的结果。（这就是为什么Redis既能快又能慢啦！）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那接下来开始讲讲我们的Redis在队列中如何实现延时的情况：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在我们日常生活中，我们可以发现：","attrs":{}}]},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在淘宝、京东等购物平台上下单，超过一定时间未付款，订单会自动取消。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"打车的时候，在规定时间没有车主接单，平台会取消你的单并提醒你暂时没有车主接单。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"点外卖的时候，如果商家在10分钟还没接单，就会自动取消订单。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"收快递的时候，如果我们没有点确认收货，在一段时间后程序会自动完成订单。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在平台完成订单后，如果我们没有在规定时间评论商品，会自动默认买家不评论。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":".......","attrs":{}}]}]}],"attrs":{}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这时，我们可以想想为什么要这样做？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"因为这样可以保证商品的库存可以释放给其他人购买，你可以不用一直等待打车却得不到回复，你可以及时换一家店点到外卖。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那么这些情况都是如何实现的呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这时我们可以看看这个图，来看看消息延迟是如何处理的：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c4/c49d3273c9d0ad1b23ac2c231e82f3f7.png","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"当用户发送一个消息请求给服务器后台的时候，服务器会检测这条消息是否需要进行延时处理，如果需要就放入到延时队列中，由延时任务检测器进行检测和处理，对于不需要进行延时处理的任务，服务器会立马对消息进行处理，并把处理后的结果返会给用户。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/af/afc69cbcf6d0ffcc3d5d3b6e52731bbb.png","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"nu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zset 这个命令，具有去重有序（分数排序）的功能。没错，你想对了呀！","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们可以使用 zset（sortedset）这个命令，用设置好的时间戳作为score进行排序，使用 zadd score1 value1 ....命令就可以一直往内存中生产消息。再利用 zrangebysocre 查询符合条件的所有待处理的任务，通过循环执行队列任务即可。也可以通过 zrangebyscore key min max withscores limit 0 1 查询最早的一条任务，来进行消费。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"总的来说，你可以通过以下两种方式来实现（(","attrs":{}},{"type":"text","marks":[{"type":"italic","attrs":{}}],"text":"^▽^","attrs":{}},{"type":"text","text":")如果你想到其他方法，也可以告诉我下呀~）：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（1）使用zrangebyscore来查询当前延时队列中所有任务，找出所有需要进行处理的延时任务，在依次进行操作。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（2）查找当前最早的一条任务，通过score值来判断任务执行的时候是否大于了当前系统的时候，比如说：最早的任务执行时间在3点，系统时间在2点58分），表示这个应该需要立马被执行啦，时间快到了（冲冲冲，他来了他来了，他带着死神的步伐来了）。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们可以想一想Redis来实现延时队列有何优势呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其实，Redis用来进行实现延时队列是具有这些优势的：","attrs":{}}]},{"type":"numberedlist","attrs":{"start":null,"normalizeStart":1},"content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"Redis zset支持高性能的 score 排序。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"Redis是在内存上进行操作的，速度非常快。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"Redis可以搭建集群，当消息很多时候，我们可以用集群来提高消息处理的速度，提高可用性。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"Redis具有持久化机制，当出现故障的时候，可以通过AOF和RDB方式来对数据进行恢复，保证了数据的可靠性","attrs":{}}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这时候，会有小伙伴问了还有没有其他实现延时队列的方式呀！emmm....当然有的，只有想不到的没有做不到。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"一、用消息中间件实现延时队列","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（1）通过 RabbitMQ 来实现延时队列","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"方法一：在MQ中我们可以对Queue设置 x-expires 过期时间或者对 Message设置超时时间x-message-ttl。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（这里要注意下：延时相同的消息我们要扔到同一个队列中，对于每一个延时要建立一个与之对应的队列—这是由于MQ的过期检测是惰性检测的。）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"方法二：我们可以用RabbitMQ的插件rabbitmq-delayed-message-exchange插件来实现延时队列。达到可投递时间时并将其通过 x-delayed-type 类型标记的交换机类型投递至目标队列。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/87/87bbf1a60e7a61f9dba3226ab4bd0954.png","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（2）RocketMQ实现延时队列","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"rocketmq在发送延时消息时，是先把消息按照延迟时间段发送到指定的队列中（把延时时间段相同的消息放到同一个队列中，保证了消息处理的顺序性，可以让同一个队列中消息延时时间是相同的，整个RocketMQ中延时消息时按照递增顺序排序，保证信息处理的先后顺序性。）。之后，通过一个定时器来轮询处理这些队列里的信息，判断是否到期。对于到期的消息会发送到相应的处理队列中，进行处理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"注意 ：目前RocketMQ只支持特定的延时时间段，1s,5s,10s,...2h，不能支持任意时间段的延时设置。有兴趣的小伙伴可以去了解下它是相关知识呀~","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"二、Kafka实现延时队","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Kafka基于时间轮自定义了一个用于实现延迟功能的定时器（SystemTimer），Kafka中的时间轮（TimingWheel）是一个存储定时任务的环形队列，可以进行相关的延时队列设置。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/91/91b919f612610224575d7f0dec69378b.png","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"三、Netty实现延时队列","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Netty也有基于时间轮算法来实现延时队列。Netty在构建延时队列主要用HashedWheelTimer，HashedWheelTimer底层数据结构是使用DelayedQueue，采用时间轮的算法来实现。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/8e/8e71db0dcece31d4bb162865c6710e08.webp","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"四、DelayQueue来实现延时队列","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Java中有自带的DelayQueue数据类型，我们可以用这个来实现延时队列。DelayQueue是封装了一个PriorityQueue（优先队列），在向DelayQueue队列中添加元素时，会给元素一个Delay（延迟时间）作为排序条件，队列中最小的元素会优先放在队首，对于队列中的元素只有到了Delay时间才允许从队列中取出。这种实现方式是数据保存在内存中，可能面临数据丢失的情况，同时它是无法支持分布式系统的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/35/35def91c112038e60ed456c9ea8704fc.webp","alt":"图片","title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"相关代码我之后会上传到我的GitHub上呀~（冲冲冲，小伙伴们！）又是美好的一天。","attrs":{}}]}]}