Unlock Real-Time Messaging: How Redis Pub/Sub Works and When to Use It

Publish‑subscribe (pub/sub) is a messaging pattern that decouples message publishers from subscribers.

Characteristics of pub/sub

Time decoupling : Publishers and subscribers do not need to be online simultaneously.

Space decoupling : Publishers and subscribers do not need to know each other's locations.

Synchronization decoupling : Interaction is asynchronous; publishers can continuously produce messages while subscribers receive them asynchronously.

Typical use cases

Real‑time messaging systems such as instant chat or group chat.

Reducing high‑concurrency I/O write pressure, e.g., logging: producers publish log messages to a channel, and a separate logger process subscribes and writes them to files or databases asynchronously.

Redis implementation of pub/sub

(1) Channels

Subscribe to one or more channels with the SUBSCRIBE command.

Example: redis> SUBSCRIBE news.it news.sport When any subscribed channel receives a new message, the client receives it.

Redis stores channel subscription relationships in the pubsub_channels dictionary, where each key is a channel name and the value is a linked list of client connections.

When a message is published to a channel, Redis looks up the corresponding list and notifies each client.

(2) Patterns

Subscribe to channels matching a pattern with the PSUBSCRIBE command.

Example: subscribe to all channels whose names start with “news.” redis> PSUBSCRIBE news.* Pattern subscription relationships are stored in the pubsub_patterns attribute, which is a linked list where each node contains a pattern and the clients subscribed to it.

When a message is published, Redis scans this list, matches the channel name against patterns, and notifies matching subscribers.