Regarding Akka message transfer performance: many small messages or less large messages?

Question

For a data-mining algorithm I am currently developing using Akka, I was wondering if Akka implements performance optimizations of the messages that are sent.

For instance, if I have an Actor that emits a very large number of messages to the same other Actor, is it good to encapsulate a set of messages into another large message? Or does Akka have some sort of buffer itself so that not one message but many messages are transfered over the network at once?

I am asking this question because the algorithm is supposed to be executed remotely on a cluster where transfer performance is important and I currently have no option to just do benchmarks myself.

Answer 1

For messages passed in Akka on the same machine, I don't think it matters a lot whether you use small message or an aggregation of messages as single message. The additional overhead of many calls versus having to loop while processing the aggregation is minimal I think. I would prefer using small messages because it keeps the system simpler.

However, when sending messages over the network Akka is using HTTP and so there is the additional HTTP overhead costs for setting up a connection etc. Therefore you might choose here to aggregate some messages into a single message. However, this also depends on your use case. Buffering implies waiting for more until there are enough (or a timeout occured). If you cannot wait, e.g. because you need fast responses, then you still need to send each message over individually.

I don't think there is a standard Akka actor available which does some aggregation of messages. Maybe a special kind of routing could be applied which does the buffering.

Or you might have a look at Akka Streams. That does support buffering of messages.