Typing indicators are ten times your messages

transcript

Online. Typing. Last seen. That chatter is ten times more traffic than your actual messages.

WhatsApp carries about 100 billion messages a day. Presence events? About a trillion a day. Every message drags along typing, stopped typing, and last seen updates. Push that down the message path? It swamps what people care about.

Messages are precious. Queued until acked, resent if lost. Presence isn't. It lives in memory only. No acks. No retries. Losing one is harmless. Last seen can lag a few seconds. Stale is fine.

Online is a memory entry with a 60-second time to live. Typing is throttled. One update a second, per chat. And it only goes to people with that chat open. Not every contact.

But here's the catch. Bob's phone dies. It never says offline. No problem. His heartbeats stop, and the entry just expires.

Keep it off the message path. Always. A presence storm must never delay a real message.

Full breakdown in the lecture.