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scalaakkaakka-httpforkjoinpool

Fork Join Pool vs Fixed Thread Pool for akka http client-focused workload?

I have a fork join dispatcher configured for a service that only uses the client side of akka http (via a host connection pool):

my-dispatcher {
  type = Dispatcher
  executor = "fork-join-executor"

  fork-join-executor {
    parallelism-min = 256
    parallelism-factor = 128.0
    parallelism-max = 2048
  }

}

The only thing the service logic does is request from an external source, unmarshal it using jawn, and then transform the jawn ast into a case class:

def get(uri: Uri)[T]: Future[T] = {
    for {
      response <- request(uri)
      json <- Unmarshal(response.entity).to[Try[JValue]]
    } yield json.transformTo[T]
  }

I was wondering if it would be more efficient to use a fixed thread pool for this kind of workload. This service gets around 150 req/s and I'd like to keep CPU usage under 1 CPU (it currently hovers at around 1.25-1.5 CPUs).

Solution

  • According to the wisdom of the ancients, your workflow is I/O bound so you should pick an execution context backed by a CachedThreadPool, however if throttling is desired you should back your context with a FixedThreadPool.

    Also, depending on the deployment environment you may be able to limit the Java process to one core at the OS level by setting CPU affinity.