This is my first post, I am database administrator and looking to use play framework version 2.4 . I have read the play 2 documentation and still have a few questions since I am very new to it. I have a messaging system that will need to handle loads of up to 50,000 blocking threads per second. If I am correct the maximum number of threads available on play are as follows:
Parallism-Factor * AvailableProcessors
Where the Parallism-Factor is the amount of threads that could be used per core? I have seen that most examples have this number as 1.0 what is wrong with going for a 100 or so? I have this P-Factor right now set at 10.0 and I have 150 cpu cores so that means that I have a maximum of 1,500 threads available if that is the case and I have to process up to 50,000 blocking requests per second then the system would be very slow right? so that the only way to scale would be to add more cores since all the requests are blocking?
'50,000 blocking requests per second' doesn't necessary mean that you need 50.000 threads to handle them. You don't need a thread for each database call.
To do a very simple calculation: Each database call takes 0.1 seconds, which is an arbitrary number since I have no clue how long your calls take. And each of those 50.000 requests lead to a single, blocking database call. Then your system needs to handle 5000 database calls per seconds. So if you have 10 CPUs you'd need 500 threads per CPU to handle them, or if you have 250 CPUs you'd need 20 threads per CPU. But this is only under ideal circumstances where those requests don't actually do anything else than blocking and waiting.
Play is using Akka for its thread management and concurrency. The advantage is that one doesn't have to care about the hassles of concurrency during your application programming any more.
Akka calculates the max number of threads with available CPUs * parallelism-factor. Additionally you can limit them with parallelism-min or parallelism-max. So if you have 250 CPUs and your parallelism-factor is 20 you have max 5000 threads available at once which might or might not be enough to handle your requests.
So to come back to your question: It's difficult to say. It depends on the time your database calls take and the how heavy you use your CPUs for other calculations. I think there is no other way but trying it out and do some performance measuring. But in general it's better to have less threads since it takes a lot of resources to create a thread. And I'd guess a parallelism-factor of 20 is a good starting point in your case for 250 CPUs.
I also found this documentation to akka-concurrency-test which itself has a good list of sources.