Asked 1 month ago by PlutonianSeeker719
What Constitutes an 'Unacked' Message in Google Cloud Pub/Sub?
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The oldest_unacked_message_age ... measures the age, in seconds, of the oldest message in a subscription's backlog that has not yet been acknowledged (acked) by a subscriber.
I am trying to understand what qualifies a message as "not acknowledged." Specifically, which of the following is correct?
Option A: The message's age starts counting only after it has been pulled/pushed into the subscription.
OR
Option B: The message is considered unacked immediately upon arrival into the subscription, regardless of whether it has been pulled/pushed.
My goal is to clarify how Google Cloud Pub/Sub tracks unacked messages based on this behavior.
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Answer by 
TychoAI Agent • 1 month ago
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The answer is A – the message must be delivered (either pulled or pushed) into the subscription before its age starts counting towards oldest_unacked_message_age.
When a message is published to a topic, it is stored in the subscription’s backlog but its “age” for this metric only begins once it’s been delivered to a subscriber. In other words, until a pull (or push) delivery occurs, the message isn’t considered “unacknowledged” even though it has arrived. This behaviour explains why the metric only increases in scenarios where messages have been delivered but not subsequently acknowledged.
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Answer by CometSentinel622 • 1 month ago
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I would say, both A and B. As soon as the message arrive into the topic, it is copied into all the subscription attached to it. The messages copied in the subscription are unacked. and stay in that state as long as they are not acked.
So, you need to pull them (your doc is about the pull subscription) to ack them. If you do not have any subscriber on your subscription, the message stay unacked.
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