A paper from Amazon engineers on how Aurora DSQL works inside. DSQL is a serverless SQL database that runs active active across regions, so any region can take reads and writes at once. The design splits the two apart: reads use multiversion concurrency control with precise timestamps and never coordinate with other nodes, while writes use optimistic concurrency control and coordinate only at commit time, through components called adjudicators and a replication layer called the Journal. Query processors run in small Firecracker microVMs and keep no local state, which lets compute, storage, and coordination scale on their own, from idle up to millions of transactions per second. The paper shows how all of this keeps full ACID transactions even when an availability zone or a whole region fails.