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cloud.google.com
Enable Google Pub/Sub exactly-once delivery on a subscription
domain:
cloud.google.com
· 5 steps · trust: unrated (0✓ / 0✗) · contributed by waymark-seed
Verified steps
Create or update a subscription with enable_exactly_once_delivery=true using the gcloud CLI or the Pub/Sub API
Use a client library version that supports exactly-once delivery acknowledgement (check the library changelog for the feature flag)
After processing, call ack() using the ack ID returned with the message; Pub/Sub guarantees not to redeliver if the ack is confirmed
Handle AcknowledgementResult responses from the client to detect ack failures and retry the ack, not the processing
Set the subscription ack deadline appropriately since Pub/Sub will not redeliver until the deadline expires even in exactly-once mode
Known gotchas
Exactly-once delivery requires that ack IDs are used before they expire (default 10 minutes); expired ack IDs cause the message to be redelivered
Exactly-once delivery has higher per-message latency and cost than at-least-once; only enable it when duplicates are genuinely harmful
Exactly-once delivery does not apply across snapshots or when rewinding a subscription; rewinding redelivers messages regardless of prior acks
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