如何通过节点接收Redis到期事件？

Question

我想听听Redis的过期事件.我在我redis.conf的配置上notify-keyspace-events "AKE",这是我在节点上的代码:

const redis = require('redis');
const client = redis.createClient();
const subscriber = redis.createClient();
const KEY_EXPIRING_TIME = 10; // seconds

client.setex('myKey', KEY_EXPIRING_TIME, 'myValue');

subscriber.on('message', function(channel, msg) {
  console.log( `On ${channel} received ${msg} event`);
});

subscriber.subscribe('myKey', function (err) {
  console.log('subscribed!');
});

我希望在10秒内看到事件被触发.setex命令工作正常,10秒内密钥不在数据库中,我在尝试捕获事件时遇到问题.

我究竟做错了什么？

Answer 1

事实上,可以使用订阅的客户端监听特定频道()并听取其消息事件的"过期"类型键事件通知.'__keyevent@db__:expired'

不需要setInterval/setTimeout或其他库

概念验证(工作:使用NodeJS v.9.4.0测试)

const redis = require('redis')
const CONF = {db:3}
var pub, sub
//.: Activate "notify-keyspace-events" for expired type events
pub = redis.createClient(CONF)
pub.send_command('config', ['set','notify-keyspace-events','Ex'], SubscribeExpired)
//.: Subscribe to the "notify-keyspace-events" channel used for expired type events
function SubscribeExpired(e,r){
 sub = redis.createClient(CONF)
 const expired_subKey = '__keyevent@'+CONF.db+'__:expired'
 sub.subscribe(expired_subKey,function(){
  console.log(' [i] Subscribed to "'+expired_subKey+'" event channel : '+r)
  sub.on('message',function (chan,msg){console.log('[expired]',msg)})
  TestKey()
 })
}
//.: For example (create a key & set to expire in 10 seconds)
function TestKey(){
 pub.set('testing','redis notify-keyspace-events : expired')
 pub.expire('testing',10)
}

Answer 2

不需要 setInterval / setTimeout 或其他库

您可以从代码下面获取每个过期的密钥。

import { createClient } from "redis";

const pub=createClient({ url: process.env.REDIS_URL });
pub.connect();
pub.configSet("notify-keyspace-events", "Ex");

const sub=pub.duplicate();
sub.connect();

sub.subscribe("__keyevent@0__:expired", (key) => {
    console.log("key=> ", key)
})

注意：此代码是使用redis@4.0.0测试的

Answer 3

方法1: -

所述的setInterval函数必须被用来检查该值是否被周期性地过期.我知道这不等于听事件.但是,它间接地起到了作用.

以下代码每5秒检查一次值.

const redis = require('redis');
const client = redis.createClient();
const subscriber = redis.createClient();
const KEY_EXPIRING_TIME = 10; // seconds

var args = ['myKey', KEY_EXPIRING_TIME,  'myValue'];


client.setex('myKey', KEY_EXPIRING_TIME, 'myValue');

subscriber.on('message', function(channel, msg) {
  console.log( `On ${channel} received ${msg} event`);
});

subscriber.subscribe('myKey', function (err) {
  console.log('subscribed!');
});

setInterval(function() {  
  client.get('myKey', function(err, value) {
    if (err) {
      throw err;
    }
    if (value) {
      console.log('value:', value);
    }
    else {
      console.log('value is gone');
      process.exit();
    }
  });
}, 5e3);

方法2: -

该redis-notifier可以用来听的事件.但是,它需要Python> = v2.5.0&<3.0.0 才能安装此软件包.

Redis的通知程序

var RedisNotifier = require('redis-notifier');

var eventNotifier = new RedisNotifier(redis, {
  redis : { host : '127.0.0.1', port : 6379 },
  expired : true,
  evicted : true,
  logLevel : 'DEBUG' //Defaults To INFO 
});

//Listen for event emission 
eventNotifier.on('message', function(pattern, channelPattern, emittedKey) {
  var channel = this.parseMessageChannel(channelPattern);
  switch(channel.key) {
    case 'expired':
        this._handleExpired(emittedKey);
      break;
    case "evicted":
      this._handleEvicted(emittedKey);
      break;
    default:
      logger.debug("Unrecognized Channel Type:" + channel.type);
  }
});