fair task queue for j2ee

Question

I intend to make a service where in people could submit tasks(specifically transcoding tasks) to the system and they should get serviced soon but at the same time it should not starve anyone else, ie it must be fair. If a person submits 2000 tasks the system should not cater to only him all the time but instead do a round robin or something like that among other people's requests...

Are there any solutions available? I looked at rabbitMQ and other messaging systems but they don't exactly cater to my problem. How are fair task queues implemented?

Answer 1

I don't think this behavior exists natively but I could see it being implemented with some of RabbitMQ's features.

http://www.rabbitmq.com/blog/2010/08/03/well-ill-let-you-go-basicreject-in-rabbitmq/

That would let you reject messages and requeue them. You would then have to write a utility that can choose to execute or requeue messages based on some identifying property of the message (in this case, the report requester, which is custom to your app). Conceivably you could design the policy entirely around the routing key if it contains the ID of the user you are trying to throttle.

Your policy could be structured using

• responding with basic.reject
• using {requeue=true}

Hopefully this helps!

Answer 2

I would implement like this:

Have a queue listener on a queue which when a message arrives checks the last time a task from the given user was received; if the time < 1 sec put it on queue 1, if time < 10 seconds put on queue 2, if time < 100 seconds put on queue 3, else put on queue 4. You would then have listeners on the 4 queues that would be processing the tasks.

Of course you can change the number of queues and change the times to match the best throughput. Ideally you want your queues to be busy all the time.