Questions about Cluster Aware Router

[Mainak Ghosh]

Hello,

I am recently playing around with cluster aware routers and distributed data and I have a few questions. I extended the multi jvm test code ReplicatedCacheSpec to create a cluster aware router which creates a pool of ReplicatedCache worker routees. Here is the code: https://gist.github.com/mghosh4/55f96a7402960923c528ea69a103c5af

When I try running this code: I get the following exception:

Failed to serialize remote message [class akka.actor.ActorSelectionMessage] using serializer [class akka.remote.serialization.MessageContainerSerializer]. Transient association error (association remains live)

[JVM-1]         at akka.remote.MessageSerializer$.serialize(MessageSerializer.scala:62)

[JVM-1]         at akka.remote.EndpointWriter.$anonfun$serializeMessage$1(Endpoint.scala:895)

[JVM-1]         at scala.util.DynamicVariable.withValue(DynamicVariable.scala:58)

[JVM-1]         at akka.remote.EndpointWriter.serializeMessage(Endpoint.scala:895)

[JVM-1]         at akka.remote.EndpointWriter.writeSend(Endpoint.scala:786)

[JVM-1]         at akka.remote.EndpointWriter$$anonfun$4.applyOrElse(Endpoint.scala:761)

[JVM-1]         at akka.actor.Actor.aroundReceive(Actor.scala:513)

[JVM-1]         at akka.actor.Actor.aroundReceive$(Actor.scala:511)

[JVM-1]         at akka.remote.EndpointActor.aroundReceive(Endpoint.scala:452)

[JVM-1]         at akka.actor.ActorCell.receiveMessage(ActorCell.scala:519)

[JVM-1]         at akka.actor.ActorCell.invoke(ActorCell.scala:488)

[JVM-1]         at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:257)

[JVM-1]         at akka.dispatch.Mailbox.run(Mailbox.scala:224)

[JVM-1]         at akka.dispatch.Mailbox.exec(Mailbox.scala:234)

[JVM-1]         at akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)

[JVM-1]         at akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)

[JVM-1]         at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)

[JVM-1]         at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

[JVM-1] Caused by: java.io.NotSerializableException: No configured serialization-bindings for class [sample.distributeddata.ReplicatedCache$PutInCache]

[JVM-1]         at akka.serialization.Serialization.serializerFor(Serialization.scala:235)

[JVM-1]         at akka.serialization.Serialization.findSerializerFor(Serialization.scala:211)

[JVM-1]         at akka.remote.serialization.MessageContainerSerializer.serializeSelection(MessageContainerSerializer.scala:35)

When I change line 83 in the gist from 

context.actorOf(FromConfig.props(ReplicatedCache.props()), name = "replicatedCache")

to

context.actorOf(ReplicatedCache.props), name = "replicatedCache")

this error goes away. Is there something that I do not understand?

Finally, I tried adding a resizer block in the configuration. I saw an exception saying something like resizer and cluster block cannot work together. Is that a current limitation?

Thanks,

Mainak

[Akka Team]

The error message says that you have not configured serialization for the message sample.distributeddata.ReplicatedCache.PutInCache which something tries to send between nodes.

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Johan

Akka Team

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[Patrik Nordwall]

Note that the intention is to use the local `Replicator` so there is not much point in delegating the message with a router to remote node, unless you use nodes with different roles, such as "frontend" and "backend" and only run distributed data on the "backend" nodes and want to send the messages from the "frontend" to the "backend" with the routers. That is probably what you are trying to do and then you must have serialization for that message.

/Patrik

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Patrik Nordwall
Akka Tech Lead
Lightbend -  Reactive apps on the JVM
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[Mainak Ghosh]

Hello Patrik and Johan,

Thanks for your reply. The goal of my work is to test the performance of resizer block in a cluster aware situation where the routees are replicators who are trying to reconcile state among themselves based on application's consistency requirement. Can you please shed some light on whether I can do this in Akka?

Here is what I have done so far. Resizers do not work with group routers. So I am using pool routers for this. I am using StatsSampleSingleMasterSpec as an example of pool based cluster aware router. I have hooked up the ReplicatedCache actor as a routee. Now I wanted to add the resizer block and it threw me an error that resizer block cannot be used along side cluster block. Can I do it programmatically or is this a limitation?

Mainak

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Mainak Ghosh

[Patrik Nordwall]

I think resizer is only for local router. Also, I don't understand why adding more actors should improve performance if the bottleneck is outside of these actors. Have you tried by just using the local replicator from each node without any routers. If not, please explain why that is not a good fit for your application.

/Patrik

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Patrik Nordwall
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Twitter: @patriknw

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Mainak Ghosh

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[Mainak Ghosh]

Hello Patrik,

I am trying to explore the tradeoffs of instantiating a new routee when there is overhead of state reconciliation. In my application, routees themselves can be CPU intensive, and as a result distributing the load across multiple machine improves performance (especially when we have a lower core count machines). Additionally, we are exploring the impact of controlled locality for remote actors.

Thanks,

Mainak

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Patrik Nordwall
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Twitter: @patriknw

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Mainak Ghosh

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Mainak Ghosh

[Mainak Ghosh]

Hello Patrik,

Any thoughts on this. We can setup a chat some time if that helps.

Mainak

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Mainak Ghosh

[Patrik Nordwall]

I'd recommend Lightbend Proffesional Support for such design consulting. If you have found an issue or bottleneck in Akka you are welcome to continue the discussion here or in the issue tracker with a reproducer of the problem.

Thanks,

Patrik