Scaling Reads vs. Writes: Where Systems Tell the Truth
Most OLTP databases are predominantly read workloads. SELECT statements outnumber INSERT, UPDATE, and DELETE by a wide margin — sometimes by an order of magnitude. Users browse and display far more often than they create or modify. Read scaling gets attention first because read pressure arrives first, and the solutions are well-understood: replicas, caches, connection pooling. It works. Writes arrive later and are more disruptive when they do. In the previous post on schema as interface , the argument was that your schema has clients who depend on certain access patterns being cheap. Writes are a new kind of client the original design often didn't account for. Indexes that accelerate reads add overhead to every write. Constraints that protect integrity can increase contention. The schema doesn't change. The workload does. And suddenly the interface is expensive in new ways. Writes expose the actual shape of your system. Not the architecture diagram shape — the real shape. Wher...