[erlang-questions] Process swarm vs Queues

Bastien CHAMAGNE <>
Fri Jul 21 10:00:06 CEST 2017


Hi,

in contrast with Dmitry, I'd chose to use a third party message broker 
(such as RabbitMQ). It's resilience is proven and I trust that their 
uptime is better than my app. Then you can have a consumer (or a pool of 
consumers) per queue.

If nothing is done, I'd chose this path.


On 20/07/2017 19:27, Dmitry Kolesnikov wrote:
> Hello,
>
> Short answer: Process swarm
>
> You'll going to implement a task scheduling routines if you choose a queuing approach. A similar task scheduling routines are already implemented by VM. You are not going to implement more efficiently then it is already done. The process pool + queue is an approach to deal with external system.
>
> The process per action is a natural approach in the actor systems. The memory overhead is reasonable, hibernate feature helps you to minimize it to few bytes. The CPU overhead  to spawn a new process is reasonable as well. You can run millions of process on the node. The process per action helps you with GC, fault tolerance and makes the implementation simple.
>
> Best Regards,
> Dmitry
>> -|-|-(*>
>> On 20 Jul 2017, at 19.49, lud <> wrote:
>>
>> Hi,
>>
>> I would like some advice regarding the design of my system.
>>
>> I have a couple of processes monitoring data endpoints on the internet, and sending events in my system when data changes.
>> Then, I have a swarm of processes dedicated to handle those events. These processes are different, it's not the same code that handles changes for different resources types (comments, feeds,
>>
>> The specific things :
>> * Processes register themselves to an ETS table to tell which resources they monitor.
>> * Processes states are very important and I can't afford to lose them. So the state is saved to disk after every handled event, and retrieved on restart.
>> * Events are quite rare, about 10 per second, whereas I could have 1000 or 10,000 monitored resources.
>>
>> At this point, I was thinking : why use a process for each resource and have so much hibernating processes. Why not just use a job queue with 10 workers, receive an event, load the data from disk, handle the event, save to disk ?
>>
>> It seems correct to me. I started with processes because it feels natural, but now I'm quite lost, I don't need all those idling processes. I feel like I was just thinking OOP (SHAME ! Just kidding …).
>>
>> How do you choose, why would you choose one of these two designs, or one another ?
>>
>> Thank you for reading
>>
>> Best regards
>>
>> Ludovic
>>
>>
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