How can I do multi-ack? about rascal

[cressie176]

I've updated v16.2.0 so you can do

ackOrNack(null, { all: true })

or

ackOrNack(err, { strategy: 'nack', all: true })

I looked at acknowledging all messages up to the current one, but because rascal keeps track of how many outstanding messages there are so that it can gracefully shutdown, this would have been a more significant change so I decided to leave it.

[cressie176]

Hi @mortiy,

It's not currently possible with Rascal. I'm not against adding it. Currently ackOrNack takes no arguments when you want to acknowledge, or an error object plus optional recovery config if you want to handle a problem, e.g. ackOrNack(err, { strategy: 'requeue' }). Changing the API to accept a boolean in place of the error object to signify multiple acknowledgments, i.e. ackOrNack(true) would be a potential, but dangerous solution as current versions of Rascal only check with the error parameter is truthy, and I suspect will nack the message if passed true. This would mean that any existing client code which passed a truthy, non-error value, would start acknowledging messages instead of nacking them.

A safer alternative would be to pass null or undefined for the error argument, and a config object as an optional second parameter. e.g. ackOrNack(null, { multiple: true }). Providing I catered for the optional callback, I think this would work well.

I'm happy to spend some time on it, or accept a tested PR (I can provide guidance), but before going further, would like to understand why you are interested in this feature. I've never found any use for multiple acknowledgements, which is why they have been overlooked until now.

[mortiy]

Hi @cressie176,

why you are interested in this feature.

I'm implementing AMQP messages batching for my task.
So I'm pre-fetching, for example, 1000 messages (without ack), collect them into single batch and process in a whole.
When I'm done (with successful result), I need acknowledge all of them.
Right now, I have to keep all 1000 ackOrNack function references to do that, but with multi-ack I could keep only the last one.

[cressie176]

OK, that makes sense. Thank you

[cressie176]

@mortiy OK to close?

[mortiy]

Yes, thank you.