Day 4

import { createClient } from 'redis';

// Subscriber needs its own connection
const subscriber = createClient();
const publisher = createClient();
await subscriber.connect();
await publisher.connect();

// Subscribe to a channel
await subscriber.subscribe('notifications', (message) => {
  console.log('Received:', JSON.parse(message));
});

// Publish from elsewhere
await publisher.publish('notifications', JSON.stringify({
  type: 'user_signup',
  userId: 123,
  email: '[email protected]'
}));

// Pattern subscribe (wildcard)
await subscriber.pSubscribe('events:*', (message, channel) => {
  console.log(`Channel ${channel}:`, message);
});

# Streams have a persistent log — messages are stored
# Consumers can read from a specific position
# Consumer groups enable parallel processing

# Add to stream
XADD events * type order_placed userId 123 amount 49.99

# Read from stream
XRANGE events - +               # all messages
XREAD COUNT 10 STREAMS events 0 # from beginning

# Consumer group (parallel workers)
XGROUP CREATE events processors $ MKSTREAM
XREADGROUP GROUP processors worker1 COUNT 1 STREAMS events >
XACK events processors   # acknowledge processed