architecture How ‘Seen’ Receipts Actually Work: Avoiding the Write Amplification Trap josedacruz, August 9, 2026August 9, 2026 TL;DR: A “seen” checkmark looks like the simplest feature in a chat app, but the naive way to build it — storing a read flag for every message and every recipient — creates a database write explosion that gets worse as your group chats grow. The fix most real apps… Continue Reading