Priority queue not working: when there are comsumers that are consuming

[Empty Empty]

Hello! I've set max priority for my queue, but messages are delivered in order they arrived.

my mq version: 3.7.9

Description: The priority is work when there are no consumers（That is, send the message and then start the consumer, the priority is work）. But there are comsumers that is comsuming, the priority is not work, messages are delivered in order they arrived.

I test with script (based on  https://gist.github.com/michaelklishin/ec056aade6ba764a27cb1ba8ca187a42) given in (https://groups.google.com/forum/#!msg/rabbitmq-users/qJ_XIUfjJUM/6Z5XfkPrEQAJ)

The script I actually use is : https://github.com/emptyknowledge/temporary/blob/master/rabbitmq_priority_not_work/priority.py

The running result is : https://github.com/emptyknowledge/temporary/blob/master/rabbitmq_priority_not_work/run_result.png

[iwe...@mail.de]

I don’t think priority should work in a stream like system. You don’t know during what time piece the priority should work. For static pool max priority could make the message ahead of any others. Just my thoughts, maybe not correct.

Regards
Wesley Peng

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[Empty Empty]

Sorry， I don't understand, for "For static pool max priority could make the message ahead of any others.", Can you explain it to me？

在 2020年2月3日星期一 UTC+8下午4:45:53，postm...@wsly.de写道：

I don’t think priority should work in a stream like system. You don’t know during what time piece the priority should work. For static pool max priority could make the message ahead of any others. Just my thoughts, maybe not correct.

Regards
Wesley Peng

> On Feb 3, 2020 - 3:53 PM, emptydr...@gmail.com wrote:
>
>
> Hello! I've set max priority for my queue, but messages are delivered in order they arrived.
>
> my mq version: 3.7.9
>
> Description: The priority is work when there are no consumers（That is, send the message and then start the consumer, the priority is work）. But there are comsumers that is comsuming, the priority is not work, messages are delivered in order they arrived.
>
> I test with script (based on  https://gist.github.com/michaelklishin/ec056aade6ba764a27cb1ba8ca187a42) given in (https://groups.google.com/forum/#!msg/rabbitmq-users/qJ_XIUfjJUM/6Z5XfkPrEQAJ)
>
> The script I actually use is : https://github.com/emptyknowledge/temporary/blob/master/rabbitmq_priority_not_work/priority.py
> The running result is : https://github.com/emptyknowledge/temporary/blob/master/rabbitmq_priority_not_work/run_result.png
>
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[Karl Nilsson]

Prioritisation will only be applied when messages need to be queued (i.e. they show up as "ready messages"). If a message arrives at the queue and can immediately be delivered to a consumer then it will, irrespective of it's priority. Given it is then the only known message on the queue apart from those currently being processed by consumers this is ok.

Try your test again with lower consumer prefetch (QoS) so that messages have to wait to be delivered. 

https://www.rabbitmq.com/priority.html

Cheers

Karl

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--

Karl Nilsson

Pivotal/RabbitMQ

[Empty Empty]

I test agin with add code "ch.basic_qos(prefetch_count=1)", the run result is same. (my pika version is 1.1.0 )  
There are codes ("time.sleep(1)")  in consumer_callback method,so the messages are queued. (send messages needing little time but somsuming is slow).

The new scripts(priority_server.py, priority_client.py) is in https://github.com/emptyknowledge/temporary/tree/master/rabbitmq_priority_not_work/add_basic_qos
.
在 2020年2月3日星期一 UTC+8下午9:00:10，Karl Nilsson写道：

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--

Karl Nilsson

Pivotal/RabbitMQ

[Wyatt Chun]

May due to time window issues.

If you want to test, give another try on prefetch=10 and sleep(10). You must have consuming slower than publishing.

Regards 

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[Empty Empty]

I test as you say, but priority still doesn't work.

Regards

在 2020年2月4日星期二 UTC+8下午12:28:32，Wyatt Chun写道：

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[Michael Klishin]

We cannot suggest anything without an executable example that demonstrates the issue.

You are asking for free support on this list, please help others help you by providing relevant information.

On an unrelated note, RabbitMQ 3.7.9 is 14 releases behind even in the 3.7.x branch.

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--

MK

Staff Software Engineer, Pivotal/RabbitMQ

[Empty Empty]

Sorry, I haven't come to the discussion group for many days， The problem is in our side, The reason is that two lines of code are written in reverse order: `ch.basic_qos(prefetch_count=1)`, `

ch.basic_consume(callback, q, no_ack=False, arguments={"x-priority": 10})`

Not working code:

```

ch.basic_consume(callback, q, no_ack=False, arguments={"x-priority": 10})

ch.basic_qos(prefetch_count=1)

ch.start_consuming()

```

Working code:

```

ch.basic_qos(prefetch_count=1)

ch.basic_consume(callback, q, no_ack=False, arguments={"x-priority": 10})

ch.start_consuming()

```

Thank you for your reply!

Regards!

在 2020年2月6日星期四 UTC+8上午5:41:06，Michael Klishin写道：

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[Michael Klishin]

Thank you for reporting back to the list. To clarify, the effects of those lines is that a consumer was added before

channel prefetch was set to 1, meaning that all deliveries have gone directly to the consumer and were not prioritised

(per the documented priority queue design choice).

It is actually possible to change prefetch for already added consumers [1] but it's a little known feature that

you don't need most of the time, and it won't make reasoning about the code easier anyway.

1. https://www.rabbitmq.com/consumer-prefetch.html

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