What is Redis pubsub and how do I use it?

Question

Somebody asked me what PubSub was and how to create a channel (in comment from my answer) and I pointed him to the article on redis.io => http://redis.io/topics/pubsub. I think it is pretty clear, but I am wondering if somebody has a better explanation. Ideally, describe it clearly using redis-cli.

Answer 1

Publish/subscribe is a pretty simple paradigm. Think of it like you're running a talk show on a radio station. That's PUBLISH. You're hoping at least one or more people will pick up your channel to listen to your messages on the radio show (SUBSCRIBE) and maybe even do some stuff, but you're not talking to folks directly.

Let's have some fun with redis-cli!

redis 127.0.0.1:6379> PUBLISH myradioshow "Good morning everyone!" (integer) 0 redis 127.0.0.1:6379> PUBLISH myradioshow "How ya'll doin tonight?" (integer) 0 redis 127.0.0.1:6379> PUBLISH myradioshow "Hello? Is anyone listening? I'm not wearing pants." (integer) 0 

Notice there are no clients receiving the messages on your "myradioshow" channel (that's the 0 in the response). Nobody is listening. Now, open another redis-cli (or for more fun times have a friend open up their redis-cli and connect to your server) and SUBSCRIBE to the channel:

redis 127.0.0.1:6379> SUBSCRIBE myradioshow Reading messages... (press Ctrl-C to quit) 1) "subscribe" 2) "myradioshow" 3) (integer) 1 

Go back to your original redis-cli and continue your show:

redis 127.0.0.1:6379> PUBLISH myradioshow "Next caller gets a free loaf of bread!" (integer) 1 

Notice that "1" at the end? You have a listener! Like magic, in your SUBSCRIBE-d terminal:

1) "message" 2) "myradioshow" 3) "Next caller gets a free loaf of bread!" 

Of course, in reality, you're probably going to want to do stuff that's more useful than telling your clients about your pants-less lifestyle, such as firing events on your server or running some kind of tasks/jobs. Maybe not though! :)