Building D1: a Global Database

What this post added

Introduces asynchronous read replication for D1 to support globally-distributed applications. Details the concept of read replicas, replica lag, and consistency models (read committed, snapshot isolation, serializable). Explains how D1 currently provides snapshot isolation via Durable Objects and the challenges of routing to consistent replicas. Proposes a new D1 Sessions API that leverages Lamport timestamps and a delay mechanism on replicas to achieve sequential consistency, enabling read-heavy workloads to utilize read replicas for lower latency and increased throughput.