Blocking calls in Akka Actors

Question

As a newbie, I am trying to understand how actors work. And, from the documentation, I think I understand that actors are objects which gets executed in sync mode and also that actor execution can contain blocking/sync method calls, e.g. db requests

But, what I don't understand is that if you write an actor that has some blocking invocations inside (like a blocking query execution), it will mess up the whole thread pool (in the sense that cpu utilization will go down, etc.), right ? I mean, from my understanding, there is no way for JVM to understand whether it can switch that thread to someone else, if/when the actor makes a blocking call.

So, given the nature of concurrency, shouldn't it be obvious that Actors should not be doing any blocking calls, ever?

If that is the case, what is the recommended way of doing a non-blocking/async call, let's say a web service call that fetches something and sends a message to another actor when that request is completed? Should we simply use something like within the actor:

future map { response => x ! response.body }

Is this the proper way of handling this?

Would appreciate it if you can clarify this for me.

Answer 1

It really depends on the use-case. If the queries do not need to be serialized, then you can execute the query in a future and send the results back to the sender as follows:

import scala.concurrent.{ future, blocking}
import akka.pattern.pipe

val resFut = future {
  blocking {
    executeQuery()
  }
}

resFut pipeTo sender

You could also create a dedicated dispatcher exclusively for the DB calls and use a router for actor creation. This way you can also easily limit the number of concurrent DB requests.