SL#155 - Architecture at Scale (3) - Discord: Put a Coalescing Layer in Front of the Database Before You Swap It

Discord went from 177 Cassandra nodes to 72 ScyllaDB nodes for trillions of messages, but the change that made the migration safe was a thin Rust layer that merges identical reads and routes every channel to one instance. Here is how the three pieces fit, what each one costs, and how to apply the idea at your size.