Adjusting the message count logic when using includeUnacked

[tbickford]

When using the RabbitMQ Scaler's includeUnacked setting to true I noticed the message count appeared to be off when I added some logging of the value of the external metric (the total message count). The value (message count) appeared to be double counting the unacknowledged message count. The current logic (before this PR) is to include the messages (count) in addition to the messages_unacknowledged (count). It appears that the HTTP Management URI messages attribute already includes the unacknowledged messages in it's value. Here is an example of some json from the HTTP Management URI:

    "messages": 498,
    "messages_details": {
      "rate": 0
    },
    "messages_paged_out": 0,
    "messages_persistent": 498,
    "messages_ram": 498,
    "messages_ready": 496,
    "messages_ready_details": {
      "rate": 0
    },
    "messages_ready_ram": 496,
    "messages_unacknowledged": 2,
    "messages_unacknowledged_details": {
      "rate": 0
    },

Note - messages_ready is 496, messages_unacknowledged is 2. The messages field is 498 (the addition of the two fields) which is what the includeUnacked setting is supposed to reflect from my understanding.

For further reference see https://www.rabbitmq.com/monitoring.html#queue-metrics messages field name - Total number of messages (ready plus unacknowledged)

[zroubalik]

@tbickford thanks. So to be clear, based on your example it currently returns 500 (498+2) instead of 498 (496+2)?

@holyketzer ^^

[holyketzer]

Oh, good catch @tbickford, I'm not very experienced user of RMQ )
yes looks like messages field includes both ready and unacked messages.

so the fix is correct

[zroubalik]

@holyketzer thanks for the confirmation.

I haven't look at the code yet, so to clarify. If Unacked msgs are already included in messages field, what is the behavior when includeUnacked == false ? Do we get 496 or 498 msgs, based on the previous example?

[tbickford]

@zroubalik When includeUnacked == false an alternative method is used to retrieve the message count which would return the number of ready messages (does not include the unacknowledged messages) https://github.com/streadway/amqp/blob/1c71cc93ed716f9a6f4c2ae8955c25f9176d9f19/channel.go#L826. So given the example above, the External Metric would show a value of 496 when setting includeUnacked == false.

[holyketzer]

@zroubalik When includeUnacked == false an alternative method is used to retrieve the message count which would return the number of ready messages (does not include the unacknowledged messages) https://github.com/streadway/amqp/blob/1c71cc93ed716f9a6f4c2ae8955c25f9176d9f19/channel.go#L826. So given the example above, the External Metric would show a value of 496 when setting includeUnacked == false.

Correct for includeUnacked == false AMQP protocol is used, and it can only returns info about ready messages.

[zroubalik]

@tbickford @holyketzer I thought it is like that, but wanted to have a clarification on this. Thanks!

[zroubalik]

LGTM, thanks @tbickford !