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PUBSUB-REDIS.md

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Redis Pub/Sub implements the messaging system where the senders (publishers) sends the messages while the receivers (subscribers) receive them. The link between the publishers and subscribers is called channel.

  • Step 1: Open two terminals.

  • Open redis-cli in the first terminal and also in the second terminal. (steps are the given below)

    • docker ps (to get the container id)
    • if not running then run the container using docker start container_id or docker start redis-stack and then docker exec -it redis-stack redis-cli or docker exec -it container_id bash and then redis-cli to open redis-cli.

  • Now write the following command in the first terminal to subscribe to the channel.

SUBSCRIBE notifications
  • Now write the following command in the second terminal to publish a message to the channel.
PUBLISH notifications "Hello, World!"
  • You will see the following output in the first terminal.
Reading messages... (press Ctrl-C to quit)

1) "subscribe"
2) "notification"
3) (integer) 1
1) "message"
2) "notification"
3) "subham"

Reading messages... (press Ctrl-C to quit)

It is beneficial when you want to scale your socket.io application. You can use redis pub/sub to communicate between multiple socket.io servers.

Some Usecases of Redis Pub/Sub

  • Chat application
  • Real-time analytics
  • Real-time notifications
  • Distributed locks
  • Distributed cache invalidation
  • Distributed session management
  • Distributed job queue
  • Distributed event-driven programming
  • Distributed publish/subscribe system
  • Distributed system monitoring
  • Distributed system coordination
  • Distributed system configuration

Cli Commands

9.1.SUBSCRIBE

This command subscribes to the specified channels.

SUBSCRIBE notifications

Reading messages... (press Ctrl-C to quit)

1) "subscribe"

2) "notifications"

3) (integer) 1
9.2.UNSUBSCRIBE

This command unsubscribes from the specified channels.

SUBSCRIBE notifications

Reading messages... (press Ctrl-C to quit)

1) "subscribe"

2) "notifications"

3) (integer) 1

UNSUBSCRIBE notifications

Reading messages... (press Ctrl-C to quit)

1) "unsubscribe"

2) "notifications"

3) (integer) 0
9.3.PUBLISH

This command publishes the specified message to the specified channel.

SUBSCRIBE notifications

Reading messages... (press Ctrl-C to quit)

1) "subscribe"

2) "notifications"

3) (integer) 1

PUBLISH notifications "Hello, World!"

(integer) 1

1) "message"

2) "notifications"

3) "Hello, World!"
9.4.PUBSUB

This command returns information about the channels.

SUBSCRIBE notifications

Reading messages... (press Ctrl-C to quit)

1) "subscribe"

2) "notifications"

3) (integer) 1

PUBSUB CHANNELS

1) "notifications"

There are a lot of other commands in redis-cli. You can check them out by typing help in redis-cli.