[rabbitmq-discuss] data being fetched from other queues too(that are not named in basicConsume)

Hi Kamal,

It looks like you are mistaking Channel.basicConsume for Channel.basicGet.
The first (which you are using) is asynchronous and what it does is
subscribe a consumer with the messaging server on a given queue. All
incoming messages to do that queue will be directly sent by the messaging
server to that subscribed consumer. In the QueuingConsumer implementation,
those received messages are held in an internal queue and you fetch them
using nextDelivery.

This model is called subscription-based, another simpler approach is using
Channel.basicGet. I advise you to check this for details:

http://www.rabbitmq.com/api-guide.html

Hi Mustafa,

Thanks for your help...

Infact, I need an asynchronous version only so that my code doesn't keep on polling the server for new messages..

My query is, if we have done something like this:

boolean autoAck = false;

System.out.println("fetching message from the Q: " + queueName + "\n");
this.channel.basicConsume(queueName, autoAck, this.queueingConsumer); // We are trying to fetch the data from the specified queue name only

QueueingConsumer.Delivery delivery;

try {
delivery = this.queueingConsumer.nextDelivery(timeout); //Shouldn't this fetch the data from the specified queue only and not some other queue(s); FYI, the same channel has been bound to a no. of queues; I hope this is not the culprit???

} catch (InterruptedException ie) {
return null;
}
if(delivery != null)
{
channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
byte[] body = delivery.getBody();
return body;
}
else
{
return null;
}

Since, in "channel.basicConsume", I have passed the name of the queue from which data has to be fetched (and not other queues too to which the channel is bound to), the why do we get data from other queues too when we do "this.queueingConsumer.nextDelivery(timeout);".

Initially, I had used "basicGet", but that will be synchronous and that's the reason why I decided to use "basicConsume".

Please also see my comments in "RED".

Also, you can see a trimmed down version of my code here:
http://pastebin.com/zLJpUFHA


Thanks & Regards,
Kamal

From: rabbitmq-discuss-bounces at lists.rabbitmq.com [mailto:rabbitmq-discuss-bounces at lists.rabbitmq.com] On Behalf Of Amr Mostafa
Sent: Monday, April 11, 2011 7:32 PM
To: Kamal
Cc: rabbitmq-discuss at lists.rabbitmq.com
Subject: Re: [rabbitmq-discuss] data being fetched from other queues too(that are not named in basicConsume)

Hi Kamal,

It looks like you are mistaking Channel.basicConsume for Channel.basicGet. The first (which you are using) is asynchronous and what it does is subscribe a consumer with the messaging server on a given queue. All incoming messages to do that queue will be directly sent by the messaging server to that subscribed consumer. In the QueuingConsumer implementation, those received messages are held in an internal queue and you fetch them using nextDelivery.

This model is called subscription-based, another simpler approach is using Channel.basicGet. I advise you to check this for details:

http://www.rabbitmq.com/api-guide.html
On Mon, Apr 11, 2011 at 3:19 PM, Kamal <kamal.nandan at gmail.comwrote:
Hi,

I am facing a strange problem while using RabbitMq.

I have a consumer that creates 3 queues(just for name sake HIGH/MEDIUM/
LOW priority queues) on the RabbitMQ server and consumes data from the
3 queues in this order:
5 messages from HIGH
3 messages from MEDIUM
2 messages from LOW.

This keeps on happening in round-robin fashion.
If there is no data available on the respective queue, the data from
the next queue is fetched.

I am using "Channel.basicConsume(queueName, ACK, QueueingConsumer)"
and "QueueingConsumer.nextDelivery(timeout)" to fetch the data.

What I see here is: I see that the data is fetched from the other
queues too. i.e. Even though I have passed the queuename as "HIGH",
then too i see that the data is being fetched from the queue "LOW" or
"MEDIUM" and vice versa. I am finding this behaviour quite strange.
Can someone plz help me out with this.

Following is a snippet of my code.:
http://pastebin.com/s03dP91z

Thanks in advance..

Regards,
Kamal
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Hi Kamal,

First off, if you want to use the asynchronous model then you don't need to
use basicConsume with each message fetch. This is something that you do at
the initialization of application/class, then you just use nextDelivery for
fetching messages.

It appears to me that you should also use 3 consumers, one for each queue.
Assuming they are called "highConsumer", "mediumConsumer" and "lowConsumer".
Then to fetch the next available message from the "high" queue you should
call: this.highConsumer.nextDelivery(), and so on.

I hope that gives you a better idea of what's wrong in your code.

Finally, there may be a way for you to

Regards,

Dear Mostafa,

Thanks a lot for your help...

I followed your recommendation and its working well for me...

Thanks again.. :)

Thanks & Regards,
Kamal

From: Amr Mostafa [mailto:amr.mostafa at gmail.com]
Sent: Tuesday, April 12, 2011 8:54 PM
To: Kamal Nandan
Cc: Kamal; rabbitmq-discuss at lists.rabbitmq.com
Subject: Re: [rabbitmq-discuss] data being fetched from other queues too(that are not named in basicConsume)

Hi Kamal,

First off, if you want to use the asynchronous model then you don't need to use basicConsume with each message fetch. This is something that you do at the initialization of application/class, then you just use nextDelivery for fetching messages.

It appears to me that you should also use 3 consumers, one for each queue. Assuming they are called "highConsumer", "mediumConsumer" and "lowConsumer". Then to fetch the next available message from the "high" queue you should call: this.highConsumer.nextDelivery(), and so on.

I hope that gives you a better idea of what's wrong in your code.

Finally, there may be a way for you to

Regards,
On Tue, Apr 12, 2011 at 8:48 AM, Kamal Nandan <kamal.nandan at impetus.co.inwrote:
Hi Mustafa,

Thanks for your help...

Infact, I need an asynchronous version only so that my code doesn't keep on polling the server for new messages..

My query is, if we have done something like this:

boolean autoAck = false;

System.out.println("fetching message from the Q: " + queueName + "\n");
this.channel.basicConsume(queueName, autoAck, this.queueingConsumer); // We are trying to fetch the data from the specified queue name only

QueueingConsumer.Delivery delivery;

try {
delivery = this.queueingConsumer.nextDelivery(timeout); //Shouldn't this fetch the data from the specified queue only and not some other queue(s); FYI, the same channel has been bound to a no. of queues; I hope this is not the culprit???

} catch (InterruptedException ie) {
return null;
}
if(delivery != null)
{
channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
byte[] body = delivery.getBody();
return body;
}
else
{
return null;
}

Since, in "channel.basicConsume", I have passed the name of the queue from which data has to be fetched (and not other queues too to which the channel is bound to), the why do we get data from other queues too when we do "this.queueingConsumer.nextDelivery(timeout);".

Initially, I had used "basicGet", but that will be synchronous and that's the reason why I decided to use "basicConsume".

Please also see my comments in "RED".

Also, you can see a trimmed down version of my code here:
http://pastebin.com/zLJpUFHA


Thanks & Regards,
Kamal

From: rabbitmq-discuss-bounces at lists.rabbitmq.com[mailto:rabbitmq-discuss-bounces at lists.rabbitmq.com<mailto:rabbitmq-discuss-bounces at lists.rabbitmq.com>] On Behalf Of Amr Mostafa
Sent: Monday, April 11, 2011 7:32 PM
To: Kamal
Cc: rabbitmq-discuss at lists.rabbitmq.com<mailto:rabbitmq-discuss at lists.rabbitmq.com>
Subject: Re: [rabbitmq-discuss] data being fetched from other queues too(that are not named in basicConsume)

Hi Kamal,

It looks like you are mistaking Channel.basicConsume for Channel.basicGet. The first (which you are using) is asynchronous and what it does is subscribe a consumer with the messaging server on a given queue. All incoming messages to do that queue will be directly sent by the messaging server to that subscribed consumer. In the QueuingConsumer implementation, those received messages are held in an internal queue and you fetch them using nextDelivery.

This model is called subscription-based, another simpler approach is using Channel.basicGet. I advise you to check this for details:

http://www.rabbitmq.com/api-guide.html
On Mon, Apr 11, 2011 at 3:19 PM, Kamal <kamal.nandan at gmail.comwrote:
Hi,

I am facing a strange problem while using RabbitMq.

I have a consumer that creates 3 queues(just for name sake HIGH/MEDIUM/
LOW priority queues) on the RabbitMQ server and consumes data from the
3 queues in this order:
5 messages from HIGH
3 messages from MEDIUM
2 messages from LOW.

This keeps on happening in round-robin fashion.
If there is no data available on the respective queue, the data from
the next queue is fetched.

I am using "Channel.basicConsume(queueName, ACK, QueueingConsumer)"
and "QueueingConsumer.nextDelivery(timeout)" to fetch the data.

What I see here is: I see that the data is fetched from the other
queues too. i.e. Even though I have passed the queuename as "HIGH",
then too i see that the data is being fetched from the queue "LOW" or
"MEDIUM" and vice versa. I am finding this behaviour quite strange.
Can someone plz help me out with this.

Following is a snippet of my code.:
http://pastebin.com/s03dP91z

Thanks in advance..

Regards,
Kamal
_______________________________________________
rabbitmq-discuss mailing list
rabbitmq-discuss at lists.rabbitmq.com<mailto:rabbitmq-discuss at lists.rabbitmq.com>
https://lists.rabbitmq.com/cgi-bin/mailman/listinfo/rabbitmq-discuss