Ack does not work

Hey there,

We are currently working on a streaming python client that reads from NATS streaming, does some processing and then publishes the result into another subject in NATS streaming. See the code below:

    # ---8< code was cut here >8---

    async def cb(msg):
        nonlocal sc
        
        # when I ack the message directly the code works fine
        # await sc.ack(msg)

        # doing some processing here to create pubmsg
        pubmsg = ...

        await sc.publish('processed', pubmsg)
        # this ack does not keep NATS streaming from resending the message after 30s
        await sc.ack(msg)

    await sc.subscribe('notprocessed', start_at='first', cb=cb, manual_acks=True, ack_wait=30)

    # ---8< code was cut here >8---

The processing takes way shorter than the 30 seconds timeout for re-sends. Pulling the ack up in the code makes this sample work like expected.

Any ideas of what we do wrong?

[juandiegopalomino]

@wallyqs awesome, it looks like we where right-- we dropped the max inflight from the default down to 10 and we haven’t gotten the issue since. Funnily enough we also did an update yesterday to log msg.sub._msgs_queue.qsize() directly (but using a property is more correct). Thank you for all your help!

[wallyqs]

@juandiegopalomino yes I think that is what might be happening, the client could be buffering several redeliveries. First will add the following to be able to confirm the status of the client buffer: https://github.com/nats-io/asyncio-nats-streaming/compare/pending-queue-size Also need to consider whether need to add some logic to the client to ignore buffered messages that have already been acked…