akka-persistence and serialization

[Eric Swenson]

Since upgrading to akka 2.4.2-RC2, I’m seeing the following warning on startup:

background log: info: [WARN] [02/04/2016 15:21:46.414] [ClusterSystem-akka.actor.default-dispatcher-25] [akka.serialization.Serialization(akka://ClusterSystem)] Using the default Java serializer for class [org.xxx.eim.ExperimentInstance$RegisterProxySucceededEvent] which is not recommended because of performance implications. Use another serializer or disable this warning using the setting 'akka.actor.warn-about-java-serializer-usage'

I’ve looked at the documentation here:  http://doc.akka.io/docs/akka/snapshot/java/serialization.html but can find no documentation on what serialization implementations are recommended or what factors to consider when choosing a serialization implementation. I’m not really keen on having to write my own serializer, nor in adding serialization methods to each of the objects used in akka-persistence. What are the recommendations here?  

— Eric

[Patrik Nordwall]

Documentation related to persistence and serialization:

http://doc.akka.io/docs/akka/2.4.1/scala/persistence.html#Custom_serialization

http://doc.akka.io/docs/akka/2.4.1/scala/persistence-schema-evolution.html

For remote messages I would use something more automatic, such as Kryo.

Regards,

Patrik

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Patrik Nordwall
Typesafe -  Reactive apps on the JVM
Twitter: @patriknw

[Paul Cleary]

Eric,

The implications of java serialization are the following:

1. It is slow to serialize and deserialize relative to other means

2. You cannot run a mixed bag.  If you have a type User that is version1, and then you change the User to be version2, if you serialize using something like akka persistence, or try to read the byte array into a User instance, your application will break.

For your application, you might not care about either of these.  If you don't have to deserialized from a stored state, then 2 wouldn't be an issue for you.

If you aren't a high throughput type of setup, then 1 may not be a concern as well.

You can quiet that setting `akka.actor.warn-about-java-serializer-use = off` (I think)

[Guido Medina]

Or, you can use something like Kryo which is kind of straight forward and very fast compared to Java serialization, for the lazy here is a quick snippet for your application conf:

akka {
  extensions = ["com.romix.akka.serialization.kryo.KryoSerializationExtension$"]

  actor {
    serializers.java = "com.romix.akka.serialization.kryo.KryoSerializer"

    kryo {
      type = "nograph"
      idstrategy = "default"
      serializer-pool-size = 1024
      kryo-reference-map = false
    }
  }
}

For more information on Kryo visit their project homepage: https://github.com/romix/akka-kryo-serialization

HTH,

Guido.