Pub/Sub Guide

SUBSCRIBE & PUBLISH

A subscribed client can only run SUBSCRIBE, PSUBSCRIBE, UNSUBSCRIBE, PUNSUBSCRIBE, PING, and RESET.

# Terminal 1: subscriber
SUBSCRIBE news:sports news:tech

# Terminal 2: publisher
PUBLISH news:sports "Team wins championship!"
PUBLISH news:tech   "New framework released"

# Subscriber receives messages in format:
# 1) "message"
# 2) "news:sports"
# 3) "Team wins championship!"

# Subscribe to multiple channels
SUBSCRIBE ch1 ch2 ch3

# Unsubscribe
UNSUBSCRIBE news:sports      # leave one channel
UNSUBSCRIBE                  # leave all channels

Pattern Subscribe (PSUBSCRIBE)

# Subscribe with glob pattern
PSUBSCRIBE news:*            # all news channels
PSUBSCRIBE user:[0-9]*       # channels matching user:NNN
PSUBSCRIBE h?llo             # hello, hallo, hxllo ...

# Received message format (pmessage):
# 1) "pmessage"
# 2) "news:*"          <- matched pattern
# 3) "news:sports"     <- actual channel
# 4) "Team wins!"      <- payload

PUNSUBSCRIBE news:*          # remove pattern subscription

# List active subscriptions
PUBSUB CHANNELS              # all active channels
PUBSUB CHANNELS news:*       # filtered
PUBSUB NUMSUB news:sports news:tech  # subscriber counts
PUBSUB NUMPAT                # number of pattern subscriptions

Keyspace Notifications

Subscribe to events triggered by Redis commands on keys (e.g., SET, EXPIRE, DEL).

# Enable keyspace notifications in redis.conf or at runtime
# K = Keyspace events  E = Keyevent events
# g = generic  $ = strings  l = lists  z = sorted sets
# x = expired  d = stream
CONFIG SET notify-keyspace-events "KEA"   # enable all

# Subscribe to keyspace channel for key "mykey"
SUBSCRIBE __keyspace@0__:mykey

# Subscribe to all expired key events
SUBSCRIBE __keyevent@0__:expired

# Subscribe to all SET operations
SUBSCRIBE __keyevent@0__:set

# Example: track session expiry
SUBSCRIBE __keyevent@0__:expired
# Receives channel: __keyevent@0__:expired
#          message: session:abc123

Node.js Pub/Sub Example

// Using ioredis (separate connections required for sub/pub)
const Redis = require("ioredis");
const pub = new Redis();
const sub = new Redis();

// Subscribe
sub.subscribe("chat:room1", (err, count) => {
  console.log(`Subscribed to ${count} channels`);
});

sub.on("message", (channel, message) => {
  console.log(`[${channel}] ${message}`);
});

// Publish
await pub.publish("chat:room1", JSON.stringify({
  user: "alice",
  text: "Hello!"
}));

// Pattern subscribe
sub.psubscribe("chat:*", (err, count) => {});
sub.on("pmessage", (pattern, channel, message) => {
  console.log(`Pattern: ${pattern}, Channel: ${channel}`);
});

Pub/Sub vs. Streams