Push subscription send multiple message much earlier than message acknowledgment deadline

Question

I set the Pubsub notification for GCS. (https://cloud.google.com/storage/docs/pubsub-notifications) And I set the Pubsub subscription to push message to GAE endpoint. With setting the message acknowledgment deadline to 90s. But when I try to create object in specified bucket, the pubsub sent multiple messages very rapidly.(see attachment)

Stack driver logging view

Steps to reproduce :

• Set the Pubsub notification for GCS (gsutil notification create -t [TOPIC] -f json -e OBJECT_FINALIZE [BUCKET])
• Create the Pubsub subscription on the specified topic, and set the subscription type to PUSH and specify GAE endpoint's url.
• Create object in the specified bucket.
• monitor log on the Stack Driver Logging.

At first it happened with a high probability but no longer occur when the number of tries over the 10 times.

Answer 1

Cloud Pub/Sub dynamically adjusts the rate of push requests based on the rate at which it receives success responses.

This means that as long as it doesn't receive an acknowledge from the subscriber, it may re-try to send the message.