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Database / REDIS

What is the purpose of Redis Pub/Sub?

Pub/Sub lets clients broadcast messages on named channels to any number of subscribers listening at that moment, without Redis storing the message anywhere — it's a pure, ephemeral fire-and-forget messaging mechanism, not a durable queue.

# subscriber
SUBSCRIBE notifications

# publisher, from a different client
PUBLISH notifications "New order received"

If no client is subscribed to a channel when a message is published, that message is simply lost — there's no backlog a late-joining subscriber can catch up on, which is the key difference from a Redis Stream. This makes Pub/Sub well suited to real-time notifications where only currently-connected clients need to know (like pushing a live update to open browser tabs), and poorly suited to anything where a message must be reliably delivered even to a consumer that wasn't listening at the exact moment it was sent.

What happens to a Pub/Sub message if no client is subscribed when it's published?
What kind of use case is Pub/Sub well suited to?

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