[akka-user] Tunning default dispatcher seems to have no effect

[Kilic Ali-Firat]

Scala version : 2.11.7
Akka version : 2.4.17

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Hi Akka Team, 

I'm writing an Akka application using Akka Cluster, Akka Actors and Akka 
Stream. I have a cluster of 3 nodes : 2 workers and 1 node consuming data 
from a source. 

I want three configs files : application.conf, node.worker.conf and 
node.source.conf. I limit the scope of this message to application.conf and 
node.worker.conf. 

Below you can find the content of node.worker.conf and application.conf : 

akka.cluster.roles = [workers]


akka {
  loglevel = "INFO"
  loglevel = ${?FGS_AKKA_LOG_LEVEL}

  actor {
    provider = "akka.cluster.ClusterActorRefProvider"

    default-dispatcher {
      # This will be used if you have set "executor = "fork-join-executor""
      fork-join-executor {
        # Min number of threads to cap factor-based parallelism number to
        parallelism-min = 1

        # The parallelism factor is used to determine thread pool size 
using the
        # following formula: ceil(available processors * factor). Resulting 
size
        # is then bounded by the parallelism-min and parallelism-max values.
        parallelism-factor = 1

        # Max number of threads to cap factor-based parallelism number to
        parallelism-max = 8
      }
      throughput = 1024
    }

  }


  remote {
    enabled-transports = ["akka.remote.netty.tcp"]
    netty.tcp {
      hostname = ${clustering.node-ip}
      port = ${clustering.node-port}




      bind-hostname = "0.0.0.0"
      bind-port = ${clustering.node-port}
    }
  }


  cluster {
    seed-nodes =
      [
        "akka.tcp://"${clustering.cluster.name}"@"${clustering.fst-seed-node
-ip}":"${clustering.fst-seed-node-port}
        "akka.tcp://"${clustering.cluster.name}"@"${clustering.snd-seed-node
-ip}":"${clustering.snd-seed-node-port}
      ]
  }
}


clustering {
  # Choose the same need port for the seed nodes. Seed nodes must be on
  # different machines.
  fst-seed-node-port = 2551
  fst-seed-node-port = ${?FGS_FIRST_SEED_NODE_PORT}

  snd-seed-node-port = 2552
  snd-seed-node-port = ${?FGS_SECOND_SEED_NODE_PORT}

  fst-seed-node-ip="localhost"
  fst-seed-node-ip=${?FGS_FIRST_SEED_NODE_IP}

  snd-seed-node-ip="localhost"
  snd-seed-node-ip=${?FGS_SECOND_SEED_NODE_IP}


//  Must be the public IP
  node-ip = ${?FGS_CLUSTER_NODE_IP}
  node-port = ${?FGS_CLUSTER_NODE_PORT}
  cluster.name = "FGS"
}


I tried to tune some settings of my default-dispatcher : I want to limit 
the number of threads in the thread pool to 8. My laptop has 8 cores, this 
is why I put the parallelism-factor to 1.0 

But looking with jvisualm the number allocated threads, I got more than 
expected (I attached a screenshot). When I expected to have only 8 threads, 
I get it 21. 

This is how I create my ActorSystem : 

val akkaConfig = ConfigFactory.load()


      val actorSystemConfig =
        (ConfigFactory parseResources "node.worker.conf")
        .withFallback(akkaConfig)
        .resolve()




    lazy val actorSystemName = akkaConfig getString clusterNamePath


    implicit val system = ActorSystem(actorSystemName, actorSystemConfig)

Am I wrong when creating my Actor System ? 

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