Acknowledge publish

[furstenheim]

When rabbit hits a memory limit it refuses published messages. According to this link:
https://groups.google.com/forum/#!topic/rabbitmq-users/OMZ7581MnEY

It is possible to publish messages to rabbit with a confirm style so that I know if the messages were correctly published. Is it possible to perform this with amqp? As channel.publish is synchronous I'm not sure.

[squaremo]

When RabbitMQ stops reading from sockets, the effect is that socket buffers fill, and eventually writes to the socket start blocking or failing. In general, NodeJS would expose this backpressure through the Stream interface, and amqplib mimics that: publish() will return false when buffers are full, and the channel will send the event 'drain' when it is OK to publish again. This is explained in the docs at http://www.squaremobius.net/amqp.node/channel_api.html#flowcontrol.

To get confirmations for published messages, use a "confirm channel": http://www.squaremobius.net/amqp.node/channel_api.html#confirmchannel.

[squaremo]

@furstenheim Did you get this working?

[furstenheim]

@squaremo Sorry for the delay, not sure that I can make it fully work. As I said, I'm taking a look at what happens when I reach the memory watermark.

I've used a confirmChannel as you suggested and then when I publish I provide a callback

    channel.publish(exchange, routingKey, content, options, function (err, result) {
      console.log(err ? 'Message nacked' : 'Message acked')})

It is better because it does not automatically return true. However, the callback is never called, it just hangs there indefinitely (>50s). Do you know if it is something on rabbitmq part? Maybe some config parameter that I have to change?

I suppose that I could always impose some timeout on the client part and close the channel if I'm getting no answer.

[srkimir]

@squaremo

will return false when buffers are full, and the channel will send the event 'drain' when it is OK to publish again.

Would not say that this will happen at least with this library. Please check following issue:
#398

[squaremo]

However, the callback is never called, it just hangs there indefinitely (>50s). Do you know if it is something on rabbitmq part?

In normal circumstances (without any special configuration, and not under load), I'd expect RabbitMQ to ack this straight away -- you would see latency about the same as a network round-trip.

If RabbitMQ is under load (e.g., hitting the memory limit), it might block the connection indefinitely, in which case it won't be reading messages from the socket, and therefore won't be confirming messages either.

Assuming normal operation, a long wait means either you or me have a bug in our code.

[cressie176]

Closing due to inactivity. For anyone experiencing problems with the publisher confirm callback not being called it can be helpful to use wireshark to inspect the communication between client and server. If you see the message being published, but no acknowledgement, then you can be confident it's either a server or a network issue. If you see the acknowledgement, then it could be a bug with your code, or amqplib, or that the client applications' event loop as become saturated.