[erlang-questions] Process swarm vs Queues

Dmitry Kolesnikov dmkolesnikov@REDACTED
Thu Jul 20 19:27:06 CEST 2017


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,

> On 20 Jul 2017, at 19.49, lud <ludovic@REDACTED> 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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