msg.ack_sync(timeout=15.0) but acknowledgment floor stays at 8

[Dylan]

Observed behavior

0. Subscribe with push to a stream category using a durable & deliver group with an ack_wait of 20.0

self.config = ConsumerConfig(
                    name=self.session
                    , deliver_group=self.session
                    , durable_name=self.session
                    , ack_wait=20
                )
await self.js.add_consumer(
                        stream=self.stream
                        , config=self.config
                        , deliver_subject=self.session
                )
self.sub = await self.js.subscribe(
                        self.category
                        , queue=self.session
                        , config=self.config
                    )

1. consume from stream & log msg output after .ack_sync()

await msg.in_progress()
# ...processing code
sync = await msg.ack_sync(timeout=15)
print(sync)

2. observe output says False for _ackd in the ack response from server

Msg(_client=<nats client v2.6.0>, subject='_INBOX.hEKvcQkCkUi1xXv9cU8mjF.hEKvcQkCkUi1xXv9cU8ugn1fed', reply='', data=b'', headers=None, _metadata=None, _ackd=False, _sid=1)

State:

  Last Delivered Message: Consumer sequence: 65,190 Stream sequence: 1,445 Last delivery: 9ms ago
    Acknowledgment Floor: Consumer sequence: 8 Stream sequence: 8 Last Ack: 2.52s ago
        Outstanding Acks: 1,000 out of maximum 1,000
    Redelivered Messages: 991
    Unprocessed Messages: 287,100
         Active Interest: Active using Queue Group bge_large_en_v15_workers

Meanwhile my middle function is humming along and running the ack_sync code for each message I convert into a payload and process, I am storing them locally on a different machine successfully.

I can only get 8 in acknowledgement floor.

Expected behavior

Acknowledgement floor goes up

Server and client version

nats-server 2.10.7
nats-py 2.6.0

Host environment

macOS Sonoma, Kubernetes chart with a 3-node cluster on Ubuntu 22

Steps to reproduce

0. Subscribe with push to a stream category using a durable & deliver group with an ack_wait of 20.0
1. consume from stream & log msg output after msg.ack_sync()
2. observe output says False for _ackd in the ack response from server, observe acknowledgement floor sticking

[Guillaume Charbonnier]

I'm not a contributor to this project, but you're printing the reply (sync) and not the original message (msg) thus it is normal that _ackd is False. If you take a look at msg._ackd you should expect True indeed.

Also, not sure why you are calling msg.in_progress() but you already have an ack_wait set to 20 so it should not be necessary to call in_progress() unless you're taking more than 20 seconds to process the message and you want to avoid a second delivery (maybe that's the case, I just wanted to warn you)

[Dylan]

unless you're taking more than 20 seconds to process the message and you want to avoid a second delivery (maybe that's the case, I just wanted to warn you)

this is indeed the case

also, I addressed the unwanted behavior by setting max unacknowledged to n where n=number of consumers in the group.