What config affects the number of threads for an ActorSystem?

[Steve Rehrauer]

I have an application that doesn't specify a custom dispatcher.

We see the number of threads maxing out at 50, and would like to increase it.

This doesn't seem to line up with any of the default config I see in Akka?  I see

     akka.actor.default-dispatcher.fork-join-executor.parallelism-max = 64

and I've tried raising this particular config, but still don't see more than 50 active threads.

How can I affect this?

[Johan Andrén]

Hi Steve,

Did you have a look at the docs about dispatcher configuration?

http://doc.akka.io/docs/akka/2.4.2/scala/dispatchers.html#default-dispatcher

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Johan Andrén

Akka Team, Lightbend Inc.

[Steve Rehrauer]

Thanks, Johan.

I did see that page, but if I understand the dispatcher config, the actor name you can define can't be a pattern?  We define many actors without simple names like "myActor".  In order to define a dispatcher for these actors, I presume I'd need to make a code change to use that dispatcher when the actors are created?

Long term, that's what I'll want to do.  Short term, I was hoping to find a pure config way to fix this.  Would be happy to override the default dispatcher's config, if that were possible, for a short-term fix.

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[Johan Andrén]

It was more this specific section of the docs I was hoping you'd notice:

1. # Configuration for the fork join pool
2. fork-join-executor {
3. # Min number of threads to cap factor-based parallelism number to
4. parallelism-min = 2
5. # Parallelism (threads) ... ceil(available processors * factor)
6. parallelism-factor = 2.0
7. # Max number of threads to cap factor-based parallelism number to
8. parallelism-max = 10
9. }
10. 
    

Note how the parallelism-max is a cap, the actual number is calculated by multiplying the number of cores with the parallelism-factor and then capping it with the min and max to arrive at the actual number on a given computer.

The specific number of 50 is hard to say anything concrete about without more info, but note that you will have a number of threads in the JVM not being dispatcher threads and even some unrelated to Akka. The dispatcher threads are easy to recognize as they are named "[systemname]-actor.default-dispatcher-[n]".

--

Johan Andrén

Akka Team, Lightbend Inc.

[Steve Rehrauer]

Ahhh, I see.  Thanks for your patience, that helps.