DDIA Learn — Designing Data-Intensive Applications

Serializable isolation is the gold standard: the result is identical to some serial execution order. Achieving it without sacrificing all concurrency is one of database engineering's hardest problems.

In practice

PostgreSQL offers SERIALIZABLE via Serializable Snapshot Isolation (SSI) — good for low-contention workloads. Google Spanner and CockroachDB use TrueTime and distributed consensus for serializable transactions across regions — at the cost of higher write latency. Redis single-threaded execution is effectively serial for one key — which is why simple counters work reliably.

Google at scale

Spanner offers externally serializable transactions globally by combining TrueTime timestamps with Paxos replication. Ad auction bidding and financial ledger rows cannot tolerate write skew across regions.

typescript — Serializable Snapshot Isolation

// Google Spanner / PostgreSQL SSI — detect conflicts at commit time
await db.query("BEGIN ISOLATION LEVEL SERIALIZABLE");
const seats = await db.query(
  "SELECT COUNT(*) FROM bookings WHERE flight_id = $1 AND seat_taken = true", [flightId]
);
if (seats.count >= maxSeats) throw new Error("flight full");
await db.query("INSERT INTO bookings (flight_id, user_id) VALUES ($1, $2)", [flightId, userId]);
await db.query("COMMIT"); // aborts if concurrent txn created a serializability conflict

Serializability