Pub/Sub ordering key

[Shayke4747]

Hi
There is a specific point regarding ordering key that I don't understand.
After a message is being published - Will subscriber with ordering key receive and process the message only after previous message with the same ordering key is acknowledged/nacked/delay is over? Or it is not waiting?

Let's assume we have 1 subscription.
Message A is being published. Subscription "gets the message", and it's started to be processed.
2 seconds later, while message A is still being processed - Message B is published to the topic (with the same ordering key).
Should I expect message B will start to be processed immedately? Or it will start to be processed only after message A is "done"?

[marckevin]

Hi @Shayke4747,

Welcome to Google Cloud Community!

As quoted from the Pub/Sub documentation:Within-key ordering:

Messages published with the same ordering key are expected to be received in order. Assume that for ordering key A, you publish messages 1, 2, and 3. With ordering enabled, 1 is expected to be delivered before 2 and 2 is expected to be delivered before 3.

Ideally for the same ordering key, Message B should not be processed immediately if Message A is still outstanding to the subscriber. Messages will be delivered in the order they were published.

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[Shayke4747]

Hi @marckevin 
WDYM by "ideally"?
Just to verify - You say that it is not guaranteed that message B will be processed only after message A is acked? I understand that "Messages will be delivered in the order they were published", but this doesn't allow me to verify the processing is done in the correct order