Acknowledge messages in NSQ

Question

I'm new to NSQ and was wondering whether it is possible to acknowledge that a message was consumed (just like in Google PubSub). I'm using Golang, and while going through the NSQ documentation (https://github.com/nsqio/nsq/blob/v1.2.1/nsqd/channel.go#L350) I've found the method FinishMessage which according to its comment, it's supposed to successfully discards an in-flight message. Would that be considered the same as acknowledged? If a message is not acknowledged in NSQ, how is it ensured it's gone once consumed so it won't be consumed over again?

Thanks

Answer 1

NSQ automatically removes a message from the queue after sending it to a consumer. And automatically re-queues the message if there is no response from the consumer after a set timeout.

And yes, depending on which programming language client you are using you have to send 'finish'. Here are the docs for Golang https://pkg.go.dev/github.com/nsqio/go-nsq#Finish

But because of the way NSQ is designed you have to re-queue a message from your app if the intended action was not successful.

Here is an excerpt from their website

NSQ guarantees that a message will be delivered at least once, though duplicate messages are possible. Consumers should expect this and de-dupe or perform idempotent operations.

This guarantee is enforced as part of the protocol and works as follows (assume the client has successfully connected and subscribed to a topic):

1. client indicates they are ready to receive messages
2. NSQ sends a message and temporarily stores the data locally (in the event of re-queue or timeout)
3. client replies FIN (finish) or REQ (re-queue) indicating success or failure respectively. If client does not reply NSQ will timeout after a configurable duration and automatically re-queue the message)

You can read more here: https://nsq.io/overview/design.html

Hope my answer helps you.