Error logging propagation when using Akka Supervision - scala

Question

Here's the thing am kinda stuck at. I have a SupervisorActor which creates Actor A and B and so on. There are no child actors to ActorA or ActorB.Lets say both Actor A and B hit Database and get SQL exception. This is propagated to the SupervisorActor up the chain. When I catch SQL exception, I also need to Log that Actor A had a SQL exception. But how can I achieve this?
1 way I could think is my Actor A logs it and throws an exception above the call stack. But I would need a try-catch block in my code. Which kinda defeats the purpose here.
Creating
Another way, I can think of is Actor A and B create a new child Actor A1 which would send it up the chain but that's not an option coz that's a common library without actors.
Is there a way to achieve something similar to :
Yes! I wanted to know if we can achieve something like:
try{
saveUser()
}
catch {
case b: BatchUpdateException =>
logger.error("We received a BatchUpdateException when trying to save the user")
throw b
}
case e: Exception =>
logger.error("Some other exception occured ")
throw e
}
try{
saveSeller()
}
catch {
case b: BatchUpdateException =>
logger.error("We received a BatchUpdateException when trying to save the Seller details")
throw b
}
case e: Exception =>
logger.error("Some other exception occured ")
throw e
}
PS: Am not sure if supervision strategy is the right approach to achieve what I am trying to achieve. I am trying to explore new possibilities.

Answer 1

Centralizing fault-handling logic within a supervisor actor using SupervisorStrategy is a better approach than scattering/duplicating it across individual actors. In particular, expressing the Exception-handling logic as the decider parameter of type PartialFunction[Throwable, Directive] helps improve code maintainability.
When I catch SQL exception, I also need to Log that Actor A had a SQL exception. But how can I achieve this?
Within the supervisor actor, you can always log Exceptions from individual child actors within the supervisor actor by including the corresponding actor references via sender. Below is a trivialized example of a supervisor actor logging actor-specific Exceptions from a couple of child actors and taking corresponding Resume/Stop/Escalate actions:
import akka.actor.{Actor, ActorSystem, Props, ActorLogging}
import akka.actor.OneForOneStrategy
import akka.actor.SupervisorStrategy._
import scala.concurrent.duration._
import java.sql.SQLException
implicit val system = ActorSystem("system")
implicit val ec = system.dispatcher
case class CreateWorker(props: Props, name: String)
case class BogusQuery(ex: Exception)
def doQuery(q: BogusQuery) = throw q.ex
class MySupervisor extends Actor with ActorLogging {
override val supervisorStrategy =
OneForOneStrategy(maxNrOfRetries = 5, withinTimeRange = 1.minute) {
case e: SQLException =>
log.error(s"Supervisor: $e from $sender; Resuming!")
Resume
case e: NullPointerException =>
log.error(s"Supervisor: $e from $sender; Stopping!")
Stop
case _: Exception =>
log.error(s"Supervisor: Unknown exception from $sender; Escalating!")
Escalate
}
def receive = {
case w: CreateWorker => sender ! context.actorOf(w.props, w.name)
}
}
class MyWorker extends Actor with ActorLogging {
def receive = {
case q: BogusQuery =>
log.info(s"$self: Received '$q'!")
doQuery(q)
case x =>
log.error(s"$self: Unknown value '${x}'!")
}
}
val supervisor = system.actorOf(Props[MySupervisor], "supervisor")
supervisor ! CreateWorker(Props[MyWorker], "workerA")
supervisor ! CreateWorker(Props[MyWorker], "workerB")
val workerA = system.actorSelection("/user/supervisor/workerA")
val workerB = system.actorSelection("/user/supervisor/workerB")
workerA ! BogusQuery(new SQLException)
// [INFO] [<timestamp>] [<dispatcher>] [akka://system/user/supervisor/workerA]
// Actor[akka://system/user/supervisor/workerA#-2129514903]:
// Received 'BogusQuery(java.sql.SQLException)'!
// [ERROR] [<timestamp>] [<dispatcher>] [akka://system/user/supervisor]
// Supervisor: java.sql.SQLException from
// Actor[akka://system/user/supervisor/workerA#-2129514903]; Resuming!
// [WARN] [<timestamp>] [<dispatcher>] [akka://system/user/supervisor/workerA] null
workerB ! BogusQuery(new NullPointerException)
// [ERROR] [<timestamp>] [<dispatcher>] [akka://system/user/supervisor]
// Supervisor: java.lang.NullPointerException from
// Actor[akka://system/user/supervisor/workerB#-1563197689]; Stopping!
// [ERROR] [<timestamp>] [<dispatcher>] [akka://system/user/supervisor/workerB] null
// java.lang.NullPointerException ...