[rabbitmq-discuss] parallel consuming from one queue

Fri Mar 25 10:16:54 GMT 2011

On 03/25/2011 09:10 AM, Jan Andersson wrote:
> On 03/24/2011 05:50 PM, Emile Joubert wrote:
>> Hi Jan,
>>
>> On 24/03/11 16:38, Jan Andersson wrote:
>>> Hi,
>>>
>>> Hi,
>>> we are trying to setup something that we hoped would be pretty straight
>>> forward but can't seem to get it to work.
>>> We want to consume messages from a persistent queue and use ack:s.
>>> However all of our attempts end in us consuming one message off the
>>> queue and then no one else (thread or process) can consume messages off
>>> the queue until that message has been ack:ed.
>>>
>>> This is in Java, we set up one channel per thread like this:
>>> [code]
>>> channel = connection.createChannel();
>>> channel.exchangeDeclare(configuration.getExchangeName(), "topic", true);
>>> channel.queueDeclare(queueName, true); // durable queue
>>> channel.queueBind(queueName, configuration.getExchangeName(),
>>> routingKey);
>>> consumer = new QueueingConsumer(channel);
>> channel.basicQos(SMALL_NUMBER);
>>
>>> channel.basicConsume(queueName, false, consumer);
>>> [/code]
>>>
>>> The ack is done like this:
>>> [code]
>>> channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
>>> [/code]
>>>
>>> Might be hard to answer this but if anyone could point us in the right
>>> direction that would be great!
>> You should set QoS on each channel. The first QueueingConsumer has
>> taken all the messages - that's why no other consumers can retrieve
>> messages. Setting QoS will prevent the broker from delivering more
>> than the set number of messages without acknowledgement and allow
>> other consumers to retrieve some messages.
>>
>> Regards
>>
>> Emile
>
> Hi,
> after setting the QoS like "channel.basicQos(1);" we can pickup messages
> in parallel.
> However, every message gets the deliveryTag set to 1. So when we ack the
> 2nd, 3rd... message we get the error:
>
> channel error; reason:
> {#method<channel.close>(reply-code=406,reply-text=PRECONDITION_FAILED -
> unknown delivery tag 1,class-id=60,method-id=80),null,""}
>
> Are we consuming the messages in the wrong way somehow?
> (QueueingConsumer.Delivery delivery = consumer.nextDelivery();)
>
> thanks for your quick reply,
> regards
> Jan
>
This was our own fault, we reused the same channel by mistake.
sorry for the bother,
Janne
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