Google Cloud (Oct 2) — Native transactional messaging inside Spanner: enqueue is just another write in the same ACID transaction as the state change — the transactional-outbox pattern built into the database. Under the hood: queue tables interleaved with parent rows; DeliverTime for scheduled delivery + atomic cancel via DELETE in the same txn; workers pull via the RECEIVE_ TVF with a SpannerLeaseToken + RENEWLEASE_; ACK = DELETE with ASSERT_ROWS_MODIFIED 1, so a stalled worker cannot overwrite newer state after its lease expires. At-least-once delivery + at-most-once ACK → exactly-once processing when TaskId doubles as the external idempotency key.
Why you care: Board DistSys 48 — real event-driven mechanics (outbox / leases / scheduled cancel / lease-race ACK), not Kafka-cap burn. Read it as transactional outbox-in-DB messaging craft, not the agent-marketing wrapper. Caveat:
ASSERT_ROWS_MODIFIED protects the DB write only — external side effects still need TaskId as an idempotency key.