Listen for changes in redis list

Question

I want to write a function that constantly listens for changes in a redis list (usually when elements are pushed to the list) and pops its elements whenever the list is not empty. Then it will execute a function on the popped elements. How should I implement this?

Answer 1

You can use notify-keyspace-events for that

example with Node.js but the idea is similar for other languages.

const Redis = require('ioredis')
const redis = new Redis()

;(async function () {
    redis.on('ready', () => {
        console.log('ready');

        redis.config('set', 'notify-keyspace-events', 'KEl')
        // KEl => see https://redis.io/topics/notifications to understand the configuration
        // l is meant we are interested in list event

        redis.psubscribe(['__key*__:*'])

        redis.on('pmessage', function(pattern, channel, message) {
            console.log('got %s', message);
        });
    })
})()

The complete list for configuration of notify-keyspace-events is here

K     Keyspace events, published with __keyspace@<db>__ prefix.
E     Keyevent events, published with __keyevent@<db>__ prefix.
g     Generic commands (non-type specific) like DEL, EXPIRE, RENAME, ...
$     String commands
l     List commands
s     Set commands
h     Hash commands
z     Sorted set commands
t     Stream commands
d     Module key type events
x     Expired events (events generated every time a key expires)
e     Evicted events (events generated when a key is evicted for maxmemory)
m     Key miss events (events generated when a key that doesn't exist is accessed)
n     New key events (Note: not included in the 'A' class)
A     Alias for "g$lshztxed", so that the "AKE" string means all the events except "m" and "n".