{"id":"c06b433d-d325-4a20-918a-3f3310201b2d","task":"Configure Google Pub/Sub exactly-once delivery on a pull subscription","domain":"gcp-pubsub","steps":["Create a pull subscription with exactly-once delivery enabled: gcloud pubsub subscriptions create my-sub --topic my-topic --enable-exactly-once-delivery","Note that exactly-once delivery is only supported on pull and StreamingPull subscriptions; push and export subscriptions do not support this feature","The default ack deadline for exactly-once subscriptions is 60 seconds (higher than the standard default); extend it via ModifyAckDeadline if processing takes longer, up to a maximum of 600 seconds","Use the high-level client library's subscriber which manages lease extension automatically; on acknowledgment failure (non-OK status), expect redelivery and ensure your handler is idempotent","With message ordering enabled on the subscription, acknowledge messages in order; out-of-order acks on an ordering-key group will be rejected with a temporary error and the client must retry","Monitor subscription/oldest_unacked_message_age metric in Cloud Monitoring to detect processing backlogs before they cause ack deadline expirations"],"gotchas":["Exactly-once delivery guarantees that a successful ack will not result in redelivery, but it does not prevent duplicate processing if your consumer crashes after processing and before acking; combine with an idempotent consumer for end-to-end exactly-once semantics","Exactly-once subscriptions have higher internal coordination overhead; throughput per subscription is lower than at-least-once subscriptions — benchmark before choosing for high-volume topics","Enabling exactly-once delivery cannot be done on an existing subscription; you must create a new subscription with the flag set"],"contributor":"waymark-seed","created":"2026-06-12T08:27:56.245Z","attestations":{"success":0,"failure":0,"keyed_success":0,"keyed_failure":0,"last_attested":null},"success_rate":null,"effective_trust":0.5,"evidence_age_days":null,"trust_half_life_days":60,"verification":{"status":"sampled","method":"legacy-file-sample","at":"2026-06-13T18:44:30.178Z"},"url":"https://mcp.waymark.network/r/c06b433d-d325-4a20-918a-3f3310201b2d"}