akka typed actor, slow "ask" with time exponentially increasing by the number of messages

[Kostas kougios]

Hi, I got this fairly simple actor:

private def actor(state: Option[R], calc: () => Future[R]): Actor.Immutable[Message] = Actor.immutable[Message] {
  (_, msg) =>
    msg match {
      case Get(replyTo) =>
        state match {
          case Some(f) =>
            replyTo ! f
            Actor.same
          case None =>
            val f = calc().awaitFor(maxWaitForFuture)
            replyTo ! f
            actor(Some(f), calc)
        }
      case Flush =>
        actor(None, calc)
    }
}

There is a blocking calc().awaitFor call, but that's not my concern right now. The actual calc returns a Future that just increases an integer, nothing more.

I have a test case for it where I send it 400 Get(--) messages using the ask pattern, i.e. actor ? Get(_) . It takes 5 seconds for the test to run. This seems too long for me. My calc() method just increases an integer (it is just a test).

More weirdly when I increase the messages to 800, the time it takes is above 20 secs!!!

I did a bit of profiling, 45% of the time is spend on

akka.actor.LightArrayRevolverScheduler$$anon$4.nextTick()

I saw the src code and it seems it sleeps a bit there conditionally.

How can I debug this slowness?

[Kostas kougios]

Did a quick test commenting out the blocking .awaitFor(). So there was no blocking call. But still it is too slow.

[Johan Andrén]

400 asks in 5 seconds should be nowhere near the number of asks/request-responses you can run through a single typed actor. Likely something in your logic or in how you measure is not quite right. 

As a reference, with a naive ping-pong test I can do around ~170 asks per ms on my machine.

Profiler showing the scheduler as cpu hotspot means your system isn't really doing anything.

If you want more help, please share the complete microbenchmark.

--

Johan

Akka Team

[Konstantinos Kougios]

It seems the slowdown was due to scalatest futureValue implicit. When I replaced it with Await.result(), the tests run fast.

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